Ship Construction
Slop tank
Water tight bulk heads
Water tight bulk heads
Questions and Answers
In the case of a ship not having a continuous bulkhead deck, the floodable length at any point may be determined to an assumed continuous margin line which at no point is less than 76 mm below the top of the deck (at side) to which the bulkheads concerned and the shell are carried watertight..
Stresses in ship structure:
Numerous forces act on a ship's structure, some of a static nature and some dynamic. The static forces are due to the differences in weight and support which occur throughout the ship, while the dynamic forces are created by the hammering of the water on the ship, the passage of waves along the ship and by the moving machinery parts. The greatest stresses set up in the ship as a whole are due to the distribution of loads along the ship, causing longitudinal bending.
The structure is strengthened to resist the effect of pounding from the collision bulkhead to 25% of the ship's length from forward. The flat bottom shell plating adjacent to the keel on each side of the ship is increased in thickness by between 15% & 30% depending upon the length of the ship, larger ships having smaller increases.
In addition to increasing the plating, the unsupported panels of plating are reduced in size. In transversely framed ships the frame spacing in this region is 700mm compared with 750mm to 900mm amid ship. Longitudinal girders are fitted 2.2m apart, extending vertically from the shell to the tank top, while intermediate half-height girders are fitted to the shell, reducing the unsupported to 1.1m. Solid floors are fitted at every frame space and are attached to the bottom shell by continuous welding.
If the bottom shell of a ship is longitudinally framed, the spacing of the longitudinal is reduced to 700mm & they are continued as far forward as practicable to the collision bulkhead. The transverse floors may be fitted at alternate frames with this arrangement and the full-height side girders may be fitted 2.1m apart. Half-height girders are not required.
When a ship is rolling it is accelerated and decelerated, resulting in forces in the structure tending to distort it. This condition is known as racking and its greatest effect is felt when the ship is in the light or ballast condition. The brackets and beam knees joining horizontal and vertical items of structure are used to resist this distortion.
Transverse bulkheads also provide considerable structural strength as support for the decks and to resist deformation caused by broadside waves (racking).
Ans:- Slop tank means a tank specifically designated for the purpose of collection of tank draining, tank washings and Other oily mixtures.
Generally there are two tanks port and starboard, located at the aft of aft most cargo tanks.
They are fitted with:-
(i) level, Interface and temperature indicators.
(ii) decanting line.
If slop tanks are required to be used for the purpose of cargo then they are to be washed clean and the remaining residue can be transfer to a residue oil tank, it is a small tank located between both slop tanks.
Answer:- Watertight bulkheads
ln addition to subdividing the ship, transverse bulkheads also provide considerable structural strength as support for the decks and to resist deformation caused by broadside waves (racking). The spacing of watertight bulkheads, which is known as the watertight subdivision of the ship, is governed by rules dependent upon ship type, size, etc. AIl ships must have:
(1) A collision or fore peak bulkhead, which is to be positioned not less than 0.05 x length of the ship, nor more than 0.08 x length of the ship, from the forward end of the load waterline.
(2) An after peak bulkhead which encloses the sterntube(s) and rudder trunk in a watertight compartment.
(3) A bulkhead at each end of the machinery space; the after bulkhead may, for an aft engine room, be the after peak bulkhead.
Additional bulkheads are to be fitted according to the vessel's length, e.g. a ship between 145 m and 165 m long must have 8 bulkheads with machinery midships and 7 bulkheads with machinery aft. Fitting less than the standard number of bulkheads is permitted in approved circumstances where additional structural compensation is provided. Watertight bulkheads must extend ta the freeboard deck but may rise to the uppermost continuous deck. The aft peak bulkhead may extend only to the next deck above the load waterline, where the construction aft of this deck is fully watertight to the shell.
The purpose of watertight subdivision and the spacing of the bulkheads is to provide an arrangement such that if one compartment is flooded between bulkheads the ship's waterline will not rise above the margin line. The margin line is a line drawn parallel to and 76 mm below the upper surface of the bulkhead deck at the ship's side. The subdivision of passenger ships is regulated by statutory requirements which are in excess of classification society rules for cargo ships, but the objects of confining flooding and avoiding sinking are the same.
Construction of watertight bulkheads:-
Watertight bulkheads, because of their large area, are formed of several strakes of plating. They are welded to the shell, deck and tank top. The plating strakes are horizontal and the stiffening is vertical. Since water pressure in a tank increases with depth and the watertight bulkhead must withstand such loading, the bulkhead must have increasingly greater strength towards the base. This is achieved by increasing the thickness of the horizontal strakes of plating towards the bottom. The collision bulkhead must have plating 12% thicker than other watertight bulkheads.
Also, plating in the aft peak bulkhead around the stern tube must be doubled or increased in thickness to reduce vibration. The bulkhead is stiffened by vertical bulb plates or toe-welded angle bar stiffeners spaced about 760 mm apart. This spacing is reduced to 610 mm for collision and oiltight bulkheads. The ends of the stiffeners are bracketed ta the tanktop and the deck beams. ln tween decks, where the loading is less, the stiffeners may have no end connections. A watertight bulkhead arrangement.
Corrugated watertight bulkheads:-
The use of corrugations or swedges in a plate instead of welded stiffeners produces as strong a structure with a reduction in weight. The troughs are vertical on transverse bulkheads but on longitudinal bulkheads they must be horizontal in order to add to the longitudinal strength of the ship.
The corrugations or swedges are made in the plating strakes prior to fabrication of the complete bulkhead. As a consequence, the strakes run vertically and the plating must be of uniform thickness and adequate to support the greater loads at the bottom of the bulkhead. This greater thickness of plate offsets to some extent the saving in weight through not adding stiffeners to the bulkhead. The edges of the corrugated bulkhead which join ta the shell plating may have stiffened flat plate fitted to increase transverse strength and simplify fitting the bulkhead to the shell.
On high bulkheads with vertical corrugations, diaphragm plates are fitted across the troughs. This prevents any possible collapse of the corrugations.
A watertight floor is fitted in the double bottom directly below every main transverse bulkhead. Where a watertight bulkhead is penetrated, e.g. by pipework, a watertight closure around the penetration must be ensured by a collar fully welded to the pipe and the bulkhead.
Testing of watertight bulkheads.
The main fore and aft peak bulkheads must be tested by filling with water to the load waterline. Subdividing watertight bulkheads are tested by hosing down. Oiltight and tank bulkheads must be tested by a head of water not less than 2.45 m above the highest point of the tank.
Non-watertight bulkheads
Any bulkheads other than those used as main subdivisions and tank boundaries may be non-watertight. Examples of the se are engine room casing bulkheads, accommodation partitions, store room division, etc. Wash bulkheads fitted in deep tanks or in the fore end of a ship are also examples of non-watertight bulkheads.
Where a non-watertight bulkhead performs the supporting function similar to a pillar, its stiffeners must be adequate for the load carried. ln all other situations the nonwatertight bulkhead is stiffened by bulb plates or simply flat plates welded edge on.
Corrugated and swedged bulkheads can also be used for non-watertight bulkheads.
Ans. Following procedure is to be followed before entry into cofferdam-
(i) Upon checking of cofferdam sounding, oil is to be pumped out to bailer fuel oil tank or bunker tank.
(ii) As there would be oil vapour present inside, the cofferdam manhole door to be opened and duly ventilated by using portable lower fan from engine room side.
(iii) A steady reading of at least 20% oxygen by volume on an oxygen content meter should be obtained before entry.
(iv) A combustible gas indicator should be used to ensure the presence of it is below the lower flammable limit
(v) No matches, welding or flame cutting equipment, electrical equipment or other sources of ignition should be taken into the space. Only tested flameproof hand lamp or torches would be allowed inside the space.
(vi) At least one attendant should be detailed to remain at the entrance to the space, whilst it is occupied.
(vii) A system of communication should be established between the attendances at the entrance and the person entering the space.
(viii) In case of any doubt, regarding the atmosphere of cofferdam breathing apparatus, Life line and rescue harness must be accompanied while entering the cofferdam.
(ix) Effort should be made to stop the leakage by applying metal putty.
The following point to be noted while handling the leaked cargo
(i) A cofferdam is a void or empty space between two bulkheads or floors which prevents leakage from one to another. It should not be left to flood with leakage oil, because the space does not have inerting system like cargo tanks, moreover leakage in the inner bulkhead may cause oil entry into machinery space causing a greater risk of fire.
(ii) Flooding with sea water is also not a good proposition as the head difference Would still cause leakage. Moreover it will increase the ships deadweight and loss of Cargo Capacity and also loss of reserve buoyancy as the void cofferdam space adds to reserve buoyancy and stability.
(iii) Sealing the cofferdam and pressurizing with air in also not viable, because it will cause unnecessary wastage of precious compressed air
(iv) Pumping the leakage oil into bunker tank is the right option which should be done from time to time as the oil level increases. The oil may be purified by using correct size gravity disc or alcap system of purification and an account of leakage oil should be kept.
Ans:- Regulation 18:- Construction and initial tests of watertight doors, side scuttles, etc., in passenger ships and cargo ships.
Sheer on the exposed decks makes the ship more seaworthy. It reduces the water coming on deck.
Raked bow:-
Raked bow designs can be said to be the most commonly used bow. It is also the most popularly used. The line of the bow is flat. It does not have any curves. The acute angle has to be less than 45 degrees. This enables the forward waterline position to allow more accommodations and especially a larger forward stateroom V-berth.
Clipper bow:-
Clipper bow designs are some of the most traditional types of bow designs. The angle at which a ship’s hull plate or planking departs from the vertical in an outward direction with increasing height is known as a flare. They are used in conjunction with rakes. Apart from easing the pitch motions flaring keeps water off the decks. Sometimes the rake is set up in such a manner that it protects the submerged portion during the collision by taking the impact first. This is known as the ‘crumple zone’. In general, these types are called clippers. The way the rake is set up here increases the center of buoyancy as well as the stability of the ship. This, in turn, increases the GM which is an important factor for the ship’s stability.
spoon bow:-
A spoon bow is a kind of bow design that convexes to the deck. It is called so because of its spoon-like appearance. This curve near the waterline is the most gradual. Such bow designs produce wave making resistance due to the curvature at their cross-section.
bulbous bows:-
In bulbous bows, there is a protruding bulb at the bow just below the waterline. Here the water flows around the hull such that it reduces drag and increased fuel efficiency (up to 12% to 15% more than those ships that don’t have a bulbous bow), speed, range, and most importantly stability. A bulbous bow increases the buoyancy of the front part and thereby decreases some of the up and down motion of the ship. They are especially effective when waterline length is longer than 15 meters and when the vessel is supposed to operate at its maximum speed most of the time. Such conditions are usually met by naval vessels, cargo ships, passenger ships, tankers, and supertankers. A bulbous bow would be detrimental to efficiency if used on smaller watercraft and thereby never used on powerboats, sailing boats, yachts, and other recreational boats. The bulbous bow does its job by producing what is called the bow wave. The bulb forces the water up forming a trough and when added to a conventional bow in the right manner cancels out the wave produced by it, hence reducing the vessel’s wake. A bulbous bow is popular in seagoing cargo ships and vessels that are larger in size.
Parabolic and Cylindrical Bows:-
Parabolic and Cylindrical Bows Compared to the straight sharp bow section ship designers sometimes tend to design blunt stems, thereby creating a parabolic shape. They are sometimes using in addition to bulbs to tackle the Wave Breaking Resistance. These bow designs are popular in bulk carriers of a fuller build. Parabolic bows have a close resemblance to cylindrical ship bows since they are also designed keeping a bigger form factor in mind. They have the ability to absolutely minimize the Wave Making Resistance if proper care is taken while designing them. They are ideal for ships in fully loaded conditions
Axe bow:-
The axe bow used in ships have a similar task too, that is cutting through the water. The long deep and narrow fore portion of the hull resembles an axe. The design includes a vertical stem line. This shape allows the ship to easily pass through the waves and keeps the up and down motion of the ship to the minimum when compared to a normal bow. The lower portion of the fore end of the hull is known as the forefoot. It remains submerged in the water and thus less open to slamming. This has its disadvantages as well because a ship with an axe bow requires more power from the rudder while maneuvering.
Inverted bow:-
An inverted bow, often known as a reverse bow is referred to those in which the most extended point is not the top, but rather the bottom. They maximize the waterline, thereby resulting in the tremendous hull speed and better hydrodynamic drag when compared to normal bows. To achieve that they sacrifice buoyancy and tend to dive under the waves instead of going above. Just like the axe bow designs the pitching (up and down motion) and slamming is much reduced resulting in a much more enjoyable journey for the crew. They are quite operable in the medium tide and are easily maneuverable. They are fuel efficient too. Another positive aspect of the bow is that it doubles up like a deck and can accommodate the personnel.
Previously they were popular on the battleships and large cruisers. But they became unpopular when newer designs came about. This was because they were not good at tackling high waves and became wet at high speed. However, they have re-entered the market with all glory and are used nowadays mostly in AHTS (Anchor Handling Tug Supply) vessels, Seismic Vessels, Offshore and Pipe-lay Vessels, drill ships, etc
Ram bow:-
A ram bow is more of an extension which is built underwater below the hull of a ship. It is a kind of a weapon which is used to pierce the hull of an enemy ship. It is not used much in today’s time but it was quite popular a few decades ago.
Before 1991 most container ships were constructed with hatch covers. Because of the longer loading and unloading times of these types of ships, the cellular type was invented. As loading and unloading occurs only vertically and the containers have standardized dimensions (TEU), large quantities of cargo can quickly be loaded using gantry cranes.
Advantages:
(a) The cargo handling is more efficient resulting in shorter time in port
(b) Guide rails hold the containers into place instead of time-consuming lashings
(c) No need of hatch covers, reducing maintenance, weight, and handling
(d) There is a high freeboard, resulting in a stronger construction
(e) Containers lashed to cellular vessels are less vulnerable to crew tampering than containers on mixed-use cargo vessels, making them less of a risk from the standpoint of port security.
Disadvantages:
(a) The high freeboard results in higher registered tonnage
(b)The price of the ship is high due to the amount of steel used and the complex design process
(c) The absence of hatch covers means that rain water and overcoming seawater can freely enter into the cargo hold. Therefore, higher requirements of bilge systems are applicable to open cargo holds
(a) Cable Stopper;
(b) Anchor windlass;
(c) Chain locker end of cable clench.
Answer: a) Cable Stopper:-
Q.2 Describe the procedure for testing, maintenance and survey of cables and associated gears.
Answer:- I. Test and maintenance
Before being accepted for service at sea all cable and associated gear are subjected to a proof load test; the proof loads of different sizes of forged steel cable are laid down by the Classification Society in the manufacturing specifications. In addition, samples of cable and associated gear are tested to destruction, in which the minimum breaking strength must not be less than 50 per cent above the proof load; for example, cable having a proof load of 100 tonnes must not fail under test below a stress of 150 tonnes.
The strength of cables may eventually decrease through wear, corrosion and fatigue, in the same way as the fittings. Fatigue is caused chiefly by the battering to which the cable is subjected when running out through the hawse pipe and the navel pipe, and when being hove in under strain. Cables are therefore surveyed periodically. The survey should bring to light any deterioration caused by wear or corrosion, and should detect any flaw or crack in a link caused by fatigue or misuse, but it will give no guide to the brittleness of the cable. The survey also provides an opportunity for rectifying minor defects, cleaning and overhauling joining shackles, and transposing the harder-worked lengths with others so that the whole cable will wear evenly. The periods at which survey and testing should take place depend on many factors, and are given in the Classification Society guidelines.
II. Procedure for survey
When berthed in a dry dock and embarking or disembarking cable, a dockyard slinger and a smith must be present, and work must be supervised by an experienced officer.
To prepare for a survey the cable lockers must first be cleared and the cable ranged (ie. laid out in fleets) on the floor of dry dock or deck or wherever convenient. If desired to range the cable along the bottom of a dry dock, permission must first be obtained from the General Manager of the dockyard.
Every shackle should be examined to ensure that the pin does not project, and should then be broken (ie parted). The machined surfaces should be cleaned and greased before reassembly, otherwise the shackles may become difficult to part. The various parts of different shackles are not interchangeable, because each shackle is made as one unit. The dovetail chamber of each shackle should be carefully reamed to remove every particle of the old lead pellet.
Lugged shackles and their bolts should be coated with soft grease, and their pins rubbed over with soft grease.
Every link and stud of chain cable is tapped with a hammer by a smith, to test it for a flaw, and Carefully examined. Should any link be found to have lost more than one-tenth of its original diameter (or one-eighth of the cable is smaller than 70 milli metres) from wear, corrosion or any other cause, the length of cable which includes the link is unfit for sea service and is to be returned to the dockyard, where the link will be replaced or the whole length condemned. A serviceable length is to be demanded,to replace any length which is condemned.
Swivels should be examined. The box-type are to be greased with a grease gun and the cups of the cup-type are to be filled with soft grease. All slips, adapter pieces and associated or spare gear are surveyed at the same time as the cable. The spare gear should be preserved by coating it with soft grease. Finally, the shackles of cable are transposed as required, to avoid undue wear on any one length, joined up together and re-marked. The inner end of the cable is then made fast to the cable clench in the locker and inspected by the Navigating Officer to confirm that it has been correctly secured; the cable is then stowed below.
Balanced and unbalanced rudder
Rudders
The rudder is used to steer the ship. The turning action is largely dependent on the area of the rudder, which is usually of the order of one-sixtieth to one-seventieth of the length x depth of the ship. The ratio of the depth to width of a rudder is known as the aspect ratio and is usually in the region of 2. Streamlined rudders of a double-plate construction are fitted to all modem ships and are further described by the arrangement about their axis.
A rudder with all of its area aft of the turning axis is known as 'unbalanced'.
A rudder with a small part of its area forward of the turning axis is known as 'semi-balanced'.
When more than 25% of the rudder area is forward of the turning axis there is no torque on the rudder stock at certain angles and such an arrangement is therefore known as a 'balanced rudder'.
Classification society rules governing windlass requires that :-
a) The windlass cable lifter brakes must be able to control the running anchor cable when the cable lifer is disconnected from the gearing while "letting go". average cable speed varies between 5 to 7.5m/sec during this operation.
b) The windlass must be capable of raising an anchor along with its chains from a depth of 82.5m to a depth of 27.5m ( 2 cable lengths) at a mean speed of not less than 9m/sec. if the depth of water is inadequate, a simulated condition can be considered.
c) The breaking effort obtained at the cable lifter must be at least equal to 40% of the breaking strength of the cable.
Although the test does not require both anchor to be lifted simultaneously, on a windlass fitted with two cable lifters, this is usually carried out and the time recorded. A visual check is made to ensure that the anchors stow correctly and that chain washing facilities are adequate.
Most anchor handling equipments incorporates one prime mover to drive two detachable cable lifters and also two wrapping ends for mooring purposes. when mooring light line speed up to 0.75 to 1m/s are required.
Name of chain drive?
Type of brake? Windlass overload in Hydraulic drive action what is slip clutch ?
Mooring or Wrapping drum purpose?
Safety feature in winches? type of crane operation?
Ans:- A strong shutter or plate fastened over a ship's porthole or cabin window in stormy weather.
Chapter part-I, Part B-2:- Openings in the shell plating below the bulkhead deck of passenger ship and the freeboard deck of cargo ships:-
1. The number of openings in the shell plating shall be reduced to the minimum compatible with the design and proper working of the ship.
2. The arrangement and efficiency of the means for closing any opening in the shell plating shall be consistent with its intended purpose and the position in which it is fitted and generally to the satisfaction of the Administration.
3.1. Subject to the requirement of the International Convention on load line in force, no side scuttle shall be fitted in such a position that its sill is below a line drawn parallel to the bulkhead deck at side and having its lowest point 2.5% of the breadth of the ship above the deepest subdivision draught, or 500mm, whichever is greater.
3.2. All side scuttles the sills of which are below the bulkhead deck of passenger ship and the freeboard deck of cargo ships, as permitted by paragraph 3.1, shall be of such construction as will effectively prevent any person opening them without the consent of the master of the ship.
4. Efficient hinged inside deadlights so arranged that they can be easily and effectively closed and secured watertight, shall be fitted to all side scuttles except that abaft one eighth of the ship's length from the forward perpendicular and above a line drawn parallel to the bulkhead deck at side and having its lowest point at height of 3.7m plus 2.5% of the breadth of the ship above the deepest subdivision draught, the deadlights may be portable in passenger accommodation, unless the deadlights are required by the load line convention to be permanently attached to their proper positions. Such portable deadlights shall be stowed adjacent to the side scuttles they surve.
5.1 No side scuttles shall be fitted in any spaces which are appropriated exclusively to the carriage of cargo.
5.2 side scuttles may, how ever be fitted in spaces appropriated alternatively to carriage of cargo or passengers, but they shall be of such construction as will effectively present any person opening them or their deadlights without the consent of the master.
6. Automatic ventilating side scuttles shall not be fitted in the shell plating below the bulkhead deck of passenger ships and the freeboard deck of cargo ships without the special sanction of the Administration.
Title-I Freeboard and Load line
Margin line and significance
Margin line. A line drawn at least 76mm below the upper surface of the bulkhead deck at side, (SOLAS). The margin line is a line defining the highest permissible location on the side of the vessel of any damage waterplane in the final condition of sinkage, trim and heel.Rise of floor
RISE OF FLOOR is the rise of the bottom shell plating above the horizontal base line, measured at the ship's side. The object is to provide for the drainage of liquids to the ship's centreline. 150mm.Freeboard types
As per International Load Line Convention(1966),There are two basic types:-
Type A Ships:- They are designed to carry only liquid cargo in bulk. They have high integrity of the exposed deck with only small access openings to cargo compartments, closed by water tight gasketed covers of steel or equivalent material. They have low permeability of loaded compartments. Have More subdivisions.
Type B ships:- All ships other than type A. They are assigned a greater freeboard than type A ship for the same length.
Type B-60 ship is any type B ship of over 100m in length which is assigned with a value of tabular freeboard which can be reduced up to 60% of the difference between the B & A type tabular values for the appropriate ship length.
Type B-100 ship is any type B ship of over 100m in length which is assigned with a value of tabular freeboard which can be reduced up to 100% of the difference between the B & A type tabular values for the appropriate ship length.
Panting
The movement of waves along a ship causes fluctuations in water pressure on the plating. This tends to create an in-and-out movement of the shell plating, known as panting. The effect is particularly evident at the bows as the ship pushes it away through the water.
The pitching motion of the ship produces additional variations in water pressure, particularly at the bow and stem, which also cause panting of the plating. Additional stiffening is provided in the form of panting beams and stringers.
Pounding or slamming results from the ship heaving or pitching, thus causing the forward region to 'slam' down onto the water. Additional structural strength must be provided from the forward perpendicular aft for 25-30% of the ship's length. The shell plating on either side of the keel is increased in thickness, depending upon the ship's minimum draught. The frame spacing is reduced, fun- and half height intercostal side girders are fitted and solid floors are installed at every frame space. With longitudinal framing the longitudinal spacing is reduced, intercostal side girders are fitted and transverse floors are installed at alternate frames.
Q. What is panting? Arrangements to prevent panting?
Ans:- Additional stiffening is provided in the fore peak structure, the transverse side framing being supported by any, or a combination of the following arrangements:
(a) Side stringers spaced vertically about 2m apart and supported by struts or beams fitted at alternate frames. These ‘panting beams’ are connected to the frames by brackets and if long may be supported at the ships centre line by a partial wash bulkhead. Intermediate frames are bracketed to the stringer.
(b) Side stringers spaced vertically about 2m apart and supported by web frames.
(c) Perforated flats spaced not more than 2.5m apart. The area of perforations being not less than 10 per cent of the total area of the flat.
Aft of the forepeak in the lower hold or deep tank spaces panting stringers are fitted in line with each stringer or perforated flat in the fore peak extending back over 15 per cent of the ship length from forward. These stringers may be omitted if the shell plating thickness is increased by 15 percent for vessels of 150m length or less decreasing linearly to 5 per cent increase for vessels of 215 m length or more. However, where the unsupported length of the main frames exceeds 9m panting stringers in line with alternate stringers or flats in the fore peak are to be fitted over 20 per cent of the ships length from forward whether the shell thickness is increased or not.
Stringers usually take the form of a web plate with flat facing bar. In tween deck spaces in the forward 15 per cent of the ships length intermediate panting stringers are fitted where the unsupported length of tween frame exceeds 2.6m in lower tween decks or 3m in upper tween decks.
Alternatively the shell thickness may be increased as above.
In the aft peak space and in deep tween decks above the aft peak similar panting arrangements are required for transverse framing except that the vertical spacing of panting stringers may be up to 2.5m apart.
If the fore peak has longitudinal framing and the depth of tank exceeds 10 m the transverse webs supporting the longitudinals are to be supported by perforated flats or an arrangement of transverse struts or beams.
Pitching
Pitching is the movement of a ship about its transverse axis. In Pitching a ship is lifted at the bow and lowered at the stern and vice versa. Pitching angles vary with the length of the vessel. In relatively short vessels they are 5° - 8° and sometimes more, while in very long vessels they are usually less than 5°.
Tanker less freeboard all reasons
a. less openings as compared to other ships and those openings can be closed efficiently.
b. they have lesser area of hatch opening compared to other ships.
c. structural strength is more & safer hence allow less freeboard.
d. it has greater subdivision by transverse and longitudinal bulkhead.
e. permeability of oil filled tank is only about 5% compared to grain cargo hold of 50-65%, so ingress in a bilge compartment will be less.{Permeability (μ) of a space is the proportion of the immersed volume of that space which can be occupied by water}.
f. density of cargo oil is less than grain cargo.
g. much large and batter pumping arrangements to control any bilge water.Floodable Length
In a ship with a continuous bulkhead deck, the floodable length at a given point is the maximum portion of the length of the ship, having its centre at the point in question, which can be flooded under the definite assumptions set forth in regulation 5 without the ship being submerged beyond the margin line.
In the case of a ship not having a continuous bulkhead deck, the floodable length at any point may be determined to an assumed continuous margin line which at no point is less than 76 mm below the top of the deck (at side) to which the bulkheads concerned and the shell are carried watertight..
Title-II Stresses in ship structures
Stresses in ship structure:
Numerous forces act on a ship's structure, some of a static nature and some dynamic. The static forces are due to the differences in weight and support which occur throughout the ship, while the dynamic forces are created by the hammering of the water on the ship, the passage of waves along the ship and by the moving machinery parts. The greatest stresses set up in the ship as a whole are due to the distribution of loads along the ship, causing longitudinal bending.
Longitudinal bending:
A ship may be regarded as non-uniform beam, carrying non-uniformly distributed weights and having varying degrees of support along its length.
A ship may be regarded as non-uniform beam, carrying non-uniformly distributed weights and having varying degrees of support along its length.
(a) Still water bending:
Consider a loaded ship lying in still water. The upthrust at any one metre length of the ship depends upon the immersed cross-sectional area of the ship at that point. If the values of upthrust at different positions along the length of the ship are plotted on a base representing the ship's length, a buoyancy curve is formed. This curve increases from zero at each end to a maximum value in way of the parallel mid-ship portion. The area of this curve represents the total upthrust exerted by the water on the ship. The total weight of a ship consists of a number of independent weights concentrated over short lengths of the ship, such as cargo, machinery, accommodation, cargo handling gear, poop and forecastle, and a number of items which form continuous material over the length of the ship, such as decks, shell and tank top. The difference between the weight and buoyancy at any point is the load at that point. In some cases the load is an excess of weight over buoyancy and in other cases an excess of buoyancy over weight. A load diagram formed by these differences is shown in the figure. Since the total weight must be equal to the total buoyancy, the area of the load diagram above the base line must be equal to the area below the base line. Because of this unequal loading, however, shearing forces and bending moments are set up in the ship. The maximum bending moment occurs about midships.
Depending upon the direction in which the bending moment acts, the ship will hog or sag. If the buoyancy amidships exceeds the weight, the ship will hog, and may be likened to a beam supported at the centre and loaded at the ends.
When a ship hogs, the deck structure is in tension while the bottom plating is in compression. If the weight amidships exceeds the buoyancy, the ship will sag, and is equivalent to a beam supported at its ends and loaded at the centre.
When a ship hogs, the deck structure is in tension while the bottom plating is in compression. If the weight amidships exceeds the buoyancy, the ship will sag, and is equivalent to a beam supported at its ends and loaded at the centre.
When a ship sags, the bottom shell is in tension while the deck is in compression. Changes in bending moment occur in a ship due to different systems of loading. This is particularly true in the case of cargoes such as iron ore which are heavy compared with the volume they occupy. If such cargo is loaded in a tramp ship, care must be taken to ensure a suitable distribution throughout the ship. Much trouble has been found in ships having machinery space and deep tank/cargo hold amidships. There is a tendency in such ships, when loading heavy cargoes, to leave the deep tank empty. This results in an excess of buoyancy in way of the deep tank. Unfortunately there is also an excess of buoyancy in way of the engine room, since the machinery is light when compared with the volume it occupies. A ship in such a loaded condition would therefore hog, creating very high stresses in the deck and bottom shell. This may be so dangerous that if owners intend the ships to be loaded in this manner, additional deck material must be provided. The structure resisting longitudinal bending consists of all continuous longitudinal material, the portions farthest from the axis of bending (the neutral axis) being the most important, e.g., keel, bottom shell, centre girder, side girders, tank top, tank margin, side shell, sheer-strake, stringer plate, deck plating alongside hatches, and in the case of oil tankers, longitudinal bulkheads. Danger may occur where a point in the structure is the greatest distance from the neutral axis, such as the top of a sheer-strake, where a high stress point occurs. Such points are to be avoided as far as possible, since a crack in the plate may result. In many oil tankers the structure is improved by joining the sheer-strake and stringer plate to form a rounded gunwale.
(b) Wave bending:
When a ship passes through waves, alterations in the distribution of buoyancy cause alterations in the bending moment. The greatest differences occur when a ship passes through waves whose lengths from crest to crest are equal to the length of the ship. When the wave crest is amidships, the buoyancy amidships is increased while at the ends it is reduced. This tends to cause the ship to hog. A few seconds later the wave trough lies amidships. The buoyancy amidships is reduced while at the ends it is increased, causing the vessel to sag. The effect of these waves is to cause fluctuations in stress, or, in extreme cases, complete reversals of stress every few seconds. Fortunately such reversals are not sufficiently numerous to cause fatigue, but will cause damage to any faulty part of the structure.
Transverse bending:
The transverse structure of a ship is subject to three different types of loading:
The transverse structure of a ship is subject to three different types of loading:
(a) forces due to the weights of the ship structure, machinery, fuel, water and cargo.
(b) water pressure.
(c) forces created by longitudinal bending.
The decks must be designed to support the weight of accommodation, winches and cargo, while exposed decks may have to withstand a tremendous weight of water shipped in heavy weather. The deck plating is connected to beams which transmit the loads to longitudinal girders and to the side frames. In way of heavy local loads such as winches, additional stiffening is arranged. The shell plating and frames form pillars which support the weights from the decks. The tank top is
required to carry the weight of the hold cargo or the upthrust exerted by the liquid in the tanks, the latter usually proving to be the most severe load. In the machinery space other factors must be taken into account. Forces of pulsating nature are transmitted through the structure due to the general out of balance forces of the machinery parts. The machinery seats must be extremely well supported to prevent any movement of the machinery. Additional girders are fitted in the double bottom and the thickness of the tank top increased under the engine in an attempt to reduce the possibility of movement which could cause severe vibration in the ship. For similar reasons the shaft and propeller must be well supported.
A considerable force is exerted on the bottom and side shell by the water surrounding the ship. The double bottom floors and side frames are designed to withstand these forces, while the shell plating must be thick enough to prevent buckling between the floors and frames. Since water pressure increases with the depth of immersion, the load on the bottom shell exceeds that on the side shell. It follows, therefore, that the bottom shell must be thicker than the side shell. When the ship passes through waves, these forces are of a pulsating nature and may vary considerably in high waves, while in bad weather conditions the shell plating above the waterline will receive severe hammering. When a ship rolls there is a tendency for the ship to distort transversely in a similar way to that in which a picture frame may collapse. This is known as racking and is reduced or prevented by the beam knee and tank side bracket connections,
together with the transverse bulkheads, the latter having the greatest effect.
required to carry the weight of the hold cargo or the upthrust exerted by the liquid in the tanks, the latter usually proving to be the most severe load. In the machinery space other factors must be taken into account. Forces of pulsating nature are transmitted through the structure due to the general out of balance forces of the machinery parts. The machinery seats must be extremely well supported to prevent any movement of the machinery. Additional girders are fitted in the double bottom and the thickness of the tank top increased under the engine in an attempt to reduce the possibility of movement which could cause severe vibration in the ship. For similar reasons the shaft and propeller must be well supported.
A considerable force is exerted on the bottom and side shell by the water surrounding the ship. The double bottom floors and side frames are designed to withstand these forces, while the shell plating must be thick enough to prevent buckling between the floors and frames. Since water pressure increases with the depth of immersion, the load on the bottom shell exceeds that on the side shell. It follows, therefore, that the bottom shell must be thicker than the side shell. When the ship passes through waves, these forces are of a pulsating nature and may vary considerably in high waves, while in bad weather conditions the shell plating above the waterline will receive severe hammering. When a ship rolls there is a tendency for the ship to distort transversely in a similar way to that in which a picture frame may collapse. This is known as racking and is reduced or prevented by the beam knee and tank side bracket connections,
together with the transverse bulkheads, the latter having the greatest effect.
The efficiency of the ship structure in withstanding longitudinal bending depends to a large extent on the ability of the transverse structure to prevent collapse of the shell plating and decks.
Docking
A ship usually enters dry dock with a slight trim aft. Thus as the water is pumped out, the after end touches the blocks. As more water is pumped out an upthrust is exerted by the blocks on the after end, causing the ship to change trim until the whole keel from forward to aft rests on the centre blocks. At the instant before this occurs the upthrust aft is a maximum. If this thrust is excessive it may be necessary to strengthen the after blocks and the after end of the ship. Such a problem arises if it is necessary to dock a ship when fully loaded or when trimming severely by the stern. As the pumping continues the load on the keel blocks is increased until the whole weight of the ship is taken by them. The ship structure in way of the keel must be strong enough to withstand this load. In most ships the normal arrangement of keel and centre girder, together with the transverse floors, is quite sufficient for the purpose. If a duct keel is fitted, however, care must be taken to ensure that the width of the duct does not exceed the width of the keel blocks. The keel structure of an oil tanker is strengthened by fitting docking brackets, tying the centre girder to the adjacent longitudinal frames at intervals of about 1.5 m. Bilge blocks or shores are fitted to support the sides of the ship. The arrangements of the bilge blocks vary from dock todock. In some cases they are fitted after the water is out of the dock, while some docks have blocks which may be slid into place while the water is still in the dock. The latter arrangement is preferable since the sides are completely supported. At the ends of the ship, the curvature of the shell does not permit blocks to be fitted and so bilge shores are used. The structure at the bilge must prevent these shores and blocks buckling the shell. As soon as the after end touches the blocks, shores are inserted between the stern and the dock side, to centralise the ship in the dock and to prevent the ship slipping off the blocks. When the ship grounds along its whole length additional shores are fitted on both sides, holding the ship in position and preventing tipping. These shores are known as breast shores and have some slight effect in preventing the side shell bulging. They should preferably be placed in way of transverse bulkheads or side frames.
Pounding When a ship meets heavy weather and commences heaving and pitching, the rise of the fore end of the ship occasionally synchronises with the trough of a wave. The fore end then emerges from the water and re-enters with a tremendous slamming effect, known as pounding. While this does not occur with great regularity, it may nevertheless cause damage to the bottom of the ship forward. The shell plating must be stiffened to prevent buckling. Pounding also occurs aft in way of the cruiser stern but the effects are not nearly as great.
Panting , if unrestricted, could eventually lead to fatigue of the material and must therefore be prevented. The structure at the ends of the ship is stiffened to prevent any undue movement of the shell.
A ship usually enters dry dock with a slight trim aft. Thus as the water is pumped out, the after end touches the blocks. As more water is pumped out an upthrust is exerted by the blocks on the after end, causing the ship to change trim until the whole keel from forward to aft rests on the centre blocks. At the instant before this occurs the upthrust aft is a maximum. If this thrust is excessive it may be necessary to strengthen the after blocks and the after end of the ship. Such a problem arises if it is necessary to dock a ship when fully loaded or when trimming severely by the stern. As the pumping continues the load on the keel blocks is increased until the whole weight of the ship is taken by them. The ship structure in way of the keel must be strong enough to withstand this load. In most ships the normal arrangement of keel and centre girder, together with the transverse floors, is quite sufficient for the purpose. If a duct keel is fitted, however, care must be taken to ensure that the width of the duct does not exceed the width of the keel blocks. The keel structure of an oil tanker is strengthened by fitting docking brackets, tying the centre girder to the adjacent longitudinal frames at intervals of about 1.5 m. Bilge blocks or shores are fitted to support the sides of the ship. The arrangements of the bilge blocks vary from dock todock. In some cases they are fitted after the water is out of the dock, while some docks have blocks which may be slid into place while the water is still in the dock. The latter arrangement is preferable since the sides are completely supported. At the ends of the ship, the curvature of the shell does not permit blocks to be fitted and so bilge shores are used. The structure at the bilge must prevent these shores and blocks buckling the shell. As soon as the after end touches the blocks, shores are inserted between the stern and the dock side, to centralise the ship in the dock and to prevent the ship slipping off the blocks. When the ship grounds along its whole length additional shores are fitted on both sides, holding the ship in position and preventing tipping. These shores are known as breast shores and have some slight effect in preventing the side shell bulging. They should preferably be placed in way of transverse bulkheads or side frames.
Pounding When a ship meets heavy weather and commences heaving and pitching, the rise of the fore end of the ship occasionally synchronises with the trough of a wave. The fore end then emerges from the water and re-enters with a tremendous slamming effect, known as pounding. While this does not occur with great regularity, it may nevertheless cause damage to the bottom of the ship forward. The shell plating must be stiffened to prevent buckling. Pounding also occurs aft in way of the cruiser stern but the effects are not nearly as great.
Panting , if unrestricted, could eventually lead to fatigue of the material and must therefore be prevented. The structure at the ends of the ship is stiffened to prevent any undue movement of the shell.
Pounding
Arrangements to resist pounding:The structure is strengthened to resist the effect of pounding from the collision bulkhead to 25% of the ship's length from forward. The flat bottom shell plating adjacent to the keel on each side of the ship is increased in thickness by between 15% & 30% depending upon the length of the ship, larger ships having smaller increases.
In addition to increasing the plating, the unsupported panels of plating are reduced in size. In transversely framed ships the frame spacing in this region is 700mm compared with 750mm to 900mm amid ship. Longitudinal girders are fitted 2.2m apart, extending vertically from the shell to the tank top, while intermediate half-height girders are fitted to the shell, reducing the unsupported to 1.1m. Solid floors are fitted at every frame space and are attached to the bottom shell by continuous welding.
If the bottom shell of a ship is longitudinally framed, the spacing of the longitudinal is reduced to 700mm & they are continued as far forward as practicable to the collision bulkhead. The transverse floors may be fitted at alternate frames with this arrangement and the full-height side girders may be fitted 2.1m apart. Half-height girders are not required.
Racking
Two structural components that will prevent Racking.When a ship is rolling it is accelerated and decelerated, resulting in forces in the structure tending to distort it. This condition is known as racking and its greatest effect is felt when the ship is in the light or ballast condition. The brackets and beam knees joining horizontal and vertical items of structure are used to resist this distortion.
Transverse bulkheads also provide considerable structural strength as support for the decks and to resist deformation caused by broadside waves (racking).
Title-III Welding and Materials
Title-IV Bottom & Side framing
Title-V Shell & Decks
Title-VI Bulkheads & Tanks
Slop tank
Q. What is a slop tank? its purpose?Ans:- Slop tank means a tank specifically designated for the purpose of collection of tank draining, tank washings and Other oily mixtures.
Generally there are two tanks port and starboard, located at the aft of aft most cargo tanks.
They are fitted with:-
(i) level, Interface and temperature indicators.
(ii) decanting line.
If slop tanks are required to be used for the purpose of cargo then they are to be washed clean and the remaining residue can be transfer to a residue oil tank, it is a small tank located between both slop tanks.
Water tight bulk heads
Question: Number of water tight bulkhead in your ship? What is it’s use? four main function?Answer:- Watertight bulkheads
ln addition to subdividing the ship, transverse bulkheads also provide considerable structural strength as support for the decks and to resist deformation caused by broadside waves (racking). The spacing of watertight bulkheads, which is known as the watertight subdivision of the ship, is governed by rules dependent upon ship type, size, etc. AIl ships must have:
(1) A collision or fore peak bulkhead, which is to be positioned not less than 0.05 x length of the ship, nor more than 0.08 x length of the ship, from the forward end of the load waterline.
(2) An after peak bulkhead which encloses the sterntube(s) and rudder trunk in a watertight compartment.
(3) A bulkhead at each end of the machinery space; the after bulkhead may, for an aft engine room, be the after peak bulkhead.
Additional bulkheads are to be fitted according to the vessel's length, e.g. a ship between 145 m and 165 m long must have 8 bulkheads with machinery midships and 7 bulkheads with machinery aft. Fitting less than the standard number of bulkheads is permitted in approved circumstances where additional structural compensation is provided. Watertight bulkheads must extend ta the freeboard deck but may rise to the uppermost continuous deck. The aft peak bulkhead may extend only to the next deck above the load waterline, where the construction aft of this deck is fully watertight to the shell.
The purpose of watertight subdivision and the spacing of the bulkheads is to provide an arrangement such that if one compartment is flooded between bulkheads the ship's waterline will not rise above the margin line. The margin line is a line drawn parallel to and 76 mm below the upper surface of the bulkhead deck at the ship's side. The subdivision of passenger ships is regulated by statutory requirements which are in excess of classification society rules for cargo ships, but the objects of confining flooding and avoiding sinking are the same.
Construction of watertight bulkheads:-
Watertight bulkheads, because of their large area, are formed of several strakes of plating. They are welded to the shell, deck and tank top. The plating strakes are horizontal and the stiffening is vertical. Since water pressure in a tank increases with depth and the watertight bulkhead must withstand such loading, the bulkhead must have increasingly greater strength towards the base. This is achieved by increasing the thickness of the horizontal strakes of plating towards the bottom. The collision bulkhead must have plating 12% thicker than other watertight bulkheads.
Also, plating in the aft peak bulkhead around the stern tube must be doubled or increased in thickness to reduce vibration. The bulkhead is stiffened by vertical bulb plates or toe-welded angle bar stiffeners spaced about 760 mm apart. This spacing is reduced to 610 mm for collision and oiltight bulkheads. The ends of the stiffeners are bracketed ta the tanktop and the deck beams. ln tween decks, where the loading is less, the stiffeners may have no end connections. A watertight bulkhead arrangement.
Corrugated watertight bulkheads:-
The use of corrugations or swedges in a plate instead of welded stiffeners produces as strong a structure with a reduction in weight. The troughs are vertical on transverse bulkheads but on longitudinal bulkheads they must be horizontal in order to add to the longitudinal strength of the ship.
The corrugations or swedges are made in the plating strakes prior to fabrication of the complete bulkhead. As a consequence, the strakes run vertically and the plating must be of uniform thickness and adequate to support the greater loads at the bottom of the bulkhead. This greater thickness of plate offsets to some extent the saving in weight through not adding stiffeners to the bulkhead. The edges of the corrugated bulkhead which join ta the shell plating may have stiffened flat plate fitted to increase transverse strength and simplify fitting the bulkhead to the shell.
On high bulkheads with vertical corrugations, diaphragm plates are fitted across the troughs. This prevents any possible collapse of the corrugations.
A watertight floor is fitted in the double bottom directly below every main transverse bulkhead. Where a watertight bulkhead is penetrated, e.g. by pipework, a watertight closure around the penetration must be ensured by a collar fully welded to the pipe and the bulkhead.
Testing of watertight bulkheads.
The main fore and aft peak bulkheads must be tested by filling with water to the load waterline. Subdividing watertight bulkheads are tested by hosing down. Oiltight and tank bulkheads must be tested by a head of water not less than 2.45 m above the highest point of the tank.
Non-watertight bulkheads
Any bulkheads other than those used as main subdivisions and tank boundaries may be non-watertight. Examples of the se are engine room casing bulkheads, accommodation partitions, store room division, etc. Wash bulkheads fitted in deep tanks or in the fore end of a ship are also examples of non-watertight bulkheads.
Where a non-watertight bulkhead performs the supporting function similar to a pillar, its stiffeners must be adequate for the load carried. ln all other situations the nonwatertight bulkhead is stiffened by bulb plates or simply flat plates welded edge on.
Corrugated and swedged bulkheads can also be used for non-watertight bulkheads.
Wing tank for VLCC
The centre tank is used for storage of cargo oil, and the wing tanks or segregated ballast tanks (SBTs) are used for carrying sea water ballast. The SBTs are epoxy coated so as to prevent corrosion.Actions to tackle leakage in cofferdam
Q. Leakage in to a cofferdam is occurring from an adjacent deep cargo tank. Action as second engineer.Ans. Following procedure is to be followed before entry into cofferdam-
(i) Upon checking of cofferdam sounding, oil is to be pumped out to bailer fuel oil tank or bunker tank.
(ii) As there would be oil vapour present inside, the cofferdam manhole door to be opened and duly ventilated by using portable lower fan from engine room side.
(iii) A steady reading of at least 20% oxygen by volume on an oxygen content meter should be obtained before entry.
(iv) A combustible gas indicator should be used to ensure the presence of it is below the lower flammable limit
(v) No matches, welding or flame cutting equipment, electrical equipment or other sources of ignition should be taken into the space. Only tested flameproof hand lamp or torches would be allowed inside the space.
(vi) At least one attendant should be detailed to remain at the entrance to the space, whilst it is occupied.
(vii) A system of communication should be established between the attendances at the entrance and the person entering the space.
(viii) In case of any doubt, regarding the atmosphere of cofferdam breathing apparatus, Life line and rescue harness must be accompanied while entering the cofferdam.
(ix) Effort should be made to stop the leakage by applying metal putty.
The following point to be noted while handling the leaked cargo
(i) A cofferdam is a void or empty space between two bulkheads or floors which prevents leakage from one to another. It should not be left to flood with leakage oil, because the space does not have inerting system like cargo tanks, moreover leakage in the inner bulkhead may cause oil entry into machinery space causing a greater risk of fire.
(ii) Flooding with sea water is also not a good proposition as the head difference Would still cause leakage. Moreover it will increase the ships deadweight and loss of Cargo Capacity and also loss of reserve buoyancy as the void cofferdam space adds to reserve buoyancy and stability.
(iii) Sealing the cofferdam and pressurizing with air in also not viable, because it will cause unnecessary wastage of precious compressed air
(iv) Pumping the leakage oil into bunker tank is the right option which should be done from time to time as the oil level increases. The oil may be purified by using correct size gravity disc or alcap system of purification and an account of leakage oil should be kept.
Watertight door requirements and regulation
Q. Watertight door requirements and regulations?Ans:- Regulation 18:- Construction and initial tests of watertight doors, side scuttles, etc., in passenger ships and cargo ships.
1. In passenger ships:
(i) the design, materials and construction of all watertight doors, side scuttles, gangway, cargo and coaling ports, valves, pipes, ash chutes and rubbish-chutes referred to in these regulations shall be to the satisfaction of the Administration;
(ii) the frames of vertical watertight doors shall have no groove at the bottom in which dirt might lodge and prevent the door closing properly.
2. In passenger ships and cargo ships each watertight door shall be tested by water pressure to a head up to the bulkhead deck or freeboard deck respectively. The test shall be made before the ship is put into service, either before or after the door is fitted.
Regulation 19:- Construction and initial tests of watertight decks, trunks, etc., in passenger ships and cargo ships.
1. Watertight decks, trunks, tunnels, duct keels and ventilators shall be of the same strength as watertight bulkheads at corresponding levels. The means used for making them watertight, and the arrangements adopted for closing openings in them, shall be to the satisfaction of the Administration.
Watertight ventilators and trunks shall be carried at least up to the bulkhead deck in passenger ships and up to the freeboard deck in cargo ships.
2. In ro–ro passenger ships where a ventilation trunk passing through a structure penetrates the bulkhead deck, the trunk shall be capable of withstanding the water pressure that may be present within the trunk, after having taken into account the maximum heel angle allowable during intermediate stages of flooding, in accordance with regulation 8.5.
3. In ro–ro passenger ships where all or part of the penetration of the bulkhead deck is on the main ro–ro deck, the trunk shall be capable of withstanding impact pressure due to internal water motions (sloshing) of water trapped on the ro–ro deck.
4. In ro–ro passenger ships constructed before 1 July 1997, the requirements of paragraphs 2 and 3 shall apply not later than the date of the first periodical survey after 1 July 1997.
5. After completion, a hose or flooding test shall be applied to watertight decks and a hose test to watertight trunks, tunnels and ventilators.
(i) the design, materials and construction of all watertight doors, side scuttles, gangway, cargo and coaling ports, valves, pipes, ash chutes and rubbish-chutes referred to in these regulations shall be to the satisfaction of the Administration;
(ii) the frames of vertical watertight doors shall have no groove at the bottom in which dirt might lodge and prevent the door closing properly.
2. In passenger ships and cargo ships each watertight door shall be tested by water pressure to a head up to the bulkhead deck or freeboard deck respectively. The test shall be made before the ship is put into service, either before or after the door is fitted.
Regulation 19:- Construction and initial tests of watertight decks, trunks, etc., in passenger ships and cargo ships.
1. Watertight decks, trunks, tunnels, duct keels and ventilators shall be of the same strength as watertight bulkheads at corresponding levels. The means used for making them watertight, and the arrangements adopted for closing openings in them, shall be to the satisfaction of the Administration.
Watertight ventilators and trunks shall be carried at least up to the bulkhead deck in passenger ships and up to the freeboard deck in cargo ships.
2. In ro–ro passenger ships where a ventilation trunk passing through a structure penetrates the bulkhead deck, the trunk shall be capable of withstanding the water pressure that may be present within the trunk, after having taken into account the maximum heel angle allowable during intermediate stages of flooding, in accordance with regulation 8.5.
3. In ro–ro passenger ships where all or part of the penetration of the bulkhead deck is on the main ro–ro deck, the trunk shall be capable of withstanding impact pressure due to internal water motions (sloshing) of water trapped on the ro–ro deck.
4. In ro–ro passenger ships constructed before 1 July 1997, the requirements of paragraphs 2 and 3 shall apply not later than the date of the first periodical survey after 1 July 1997.
5. After completion, a hose or flooding test shall be applied to watertight decks and a hose test to watertight trunks, tunnels and ventilators.
Title-VII Fore end Arrangements
Sheer and its purpose
Sheer is the curvature of deck in fore and aft of ship, rising from the midship to a maximum at the ends. The sheer forward is usually twice that at the aft.Sheer on the exposed decks makes the ship more seaworthy. It reduces the water coming on deck.
Types of bow
Plumb bow:- What we today call a normal bow has evolved from what was previously a vertical bow. Rake may be defined as the angle the ship stem makes with the waterline. This bow has the maximum waterline length of all. A straight edged vertical bow that is perpendicular to the waters is known as a plumb bow. If we don’t include an X-bow or Inverted bow, they happened to have the maximum waterline. This is what enables it to attain greater hull speed.Raked bow:-
Raked bow designs can be said to be the most commonly used bow. It is also the most popularly used. The line of the bow is flat. It does not have any curves. The acute angle has to be less than 45 degrees. This enables the forward waterline position to allow more accommodations and especially a larger forward stateroom V-berth.
Clipper bow:-
Clipper bow designs are some of the most traditional types of bow designs. The angle at which a ship’s hull plate or planking departs from the vertical in an outward direction with increasing height is known as a flare. They are used in conjunction with rakes. Apart from easing the pitch motions flaring keeps water off the decks. Sometimes the rake is set up in such a manner that it protects the submerged portion during the collision by taking the impact first. This is known as the ‘crumple zone’. In general, these types are called clippers. The way the rake is set up here increases the center of buoyancy as well as the stability of the ship. This, in turn, increases the GM which is an important factor for the ship’s stability.
spoon bow:-
A spoon bow is a kind of bow design that convexes to the deck. It is called so because of its spoon-like appearance. This curve near the waterline is the most gradual. Such bow designs produce wave making resistance due to the curvature at their cross-section.
bulbous bows:-
In bulbous bows, there is a protruding bulb at the bow just below the waterline. Here the water flows around the hull such that it reduces drag and increased fuel efficiency (up to 12% to 15% more than those ships that don’t have a bulbous bow), speed, range, and most importantly stability. A bulbous bow increases the buoyancy of the front part and thereby decreases some of the up and down motion of the ship. They are especially effective when waterline length is longer than 15 meters and when the vessel is supposed to operate at its maximum speed most of the time. Such conditions are usually met by naval vessels, cargo ships, passenger ships, tankers, and supertankers. A bulbous bow would be detrimental to efficiency if used on smaller watercraft and thereby never used on powerboats, sailing boats, yachts, and other recreational boats. The bulbous bow does its job by producing what is called the bow wave. The bulb forces the water up forming a trough and when added to a conventional bow in the right manner cancels out the wave produced by it, hence reducing the vessel’s wake. A bulbous bow is popular in seagoing cargo ships and vessels that are larger in size.
Parabolic and Cylindrical Bows:-
Parabolic and Cylindrical Bows Compared to the straight sharp bow section ship designers sometimes tend to design blunt stems, thereby creating a parabolic shape. They are sometimes using in addition to bulbs to tackle the Wave Breaking Resistance. These bow designs are popular in bulk carriers of a fuller build. Parabolic bows have a close resemblance to cylindrical ship bows since they are also designed keeping a bigger form factor in mind. They have the ability to absolutely minimize the Wave Making Resistance if proper care is taken while designing them. They are ideal for ships in fully loaded conditions
Axe bow:-
The axe bow used in ships have a similar task too, that is cutting through the water. The long deep and narrow fore portion of the hull resembles an axe. The design includes a vertical stem line. This shape allows the ship to easily pass through the waves and keeps the up and down motion of the ship to the minimum when compared to a normal bow. The lower portion of the fore end of the hull is known as the forefoot. It remains submerged in the water and thus less open to slamming. This has its disadvantages as well because a ship with an axe bow requires more power from the rudder while maneuvering.
Inverted bow:-
An inverted bow, often known as a reverse bow is referred to those in which the most extended point is not the top, but rather the bottom. They maximize the waterline, thereby resulting in the tremendous hull speed and better hydrodynamic drag when compared to normal bows. To achieve that they sacrifice buoyancy and tend to dive under the waves instead of going above. Just like the axe bow designs the pitching (up and down motion) and slamming is much reduced resulting in a much more enjoyable journey for the crew. They are quite operable in the medium tide and are easily maneuverable. They are fuel efficient too. Another positive aspect of the bow is that it doubles up like a deck and can accommodate the personnel.
Previously they were popular on the battleships and large cruisers. But they became unpopular when newer designs came about. This was because they were not good at tackling high waves and became wet at high speed. However, they have re-entered the market with all glory and are used nowadays mostly in AHTS (Anchor Handling Tug Supply) vessels, Seismic Vessels, Offshore and Pipe-lay Vessels, drill ships, etc
Ram bow:-
A ram bow is more of an extension which is built underwater below the hull of a ship. It is a kind of a weapon which is used to pierce the hull of an enemy ship. It is not used much in today’s time but it was quite popular a few decades ago.
Fore Peak tank Construction:
Tanks located at the extreme end of the ship are termed as peak tanks. Tanks at the fore end of the ship is termed as Fore Peak tank, tank at the aft end of the ship is termed as Aft Peak Tank. Fore peak tank is the volume enclosed between the Collision bulkhead, ship's hull plating and the fore peak tank top.
This tank is located in the high stress regions of the ship, hence it is fitted with special strengthening arrangements termed as panting arrangements. Access to this tank Is provided through manhole located on the tank top.
It is a watertight tank normally used for ballast purposes for proper trim especially on the ballast voyage.
A watertight collision bulkhead is fitted in the fore peak tank to minimize the damage to the cargo located aft of the collision bulkhead in the event of a collision. The chain locker for storing the anchor chain is normally located inside the fore peak tank.
This tank is located in the high stress regions of the ship, hence it is fitted with special strengthening arrangements termed as panting arrangements. Access to this tank Is provided through manhole located on the tank top.
It is a watertight tank normally used for ballast purposes for proper trim especially on the ballast voyage.
A watertight collision bulkhead is fitted in the fore peak tank to minimize the damage to the cargo located aft of the collision bulkhead in the event of a collision. The chain locker for storing the anchor chain is normally located inside the fore peak tank.
The following structures are found in the fore peak tank:
1. Stem plate or stem bar or a combination of both in the forward most structure, which forms the profile of the bow. The stern plate is normally made of steel plate and is stiffened by a center line girder or stiffener. The stem runs from the highest point at the forecastle to the keel of the ship.
2. Breast hooks are fitted at intervals to stiffen the stem plate and to connect the stem plate to the panting stringers or side stringers.
3. Deck head is the uppermost deck of the fore peak tank which Is watertight. Entry to the fore peak tank is through man holes which are kept watertight by covers when ship is under way.
4. Panting stringers or side stringers are fitted at regular intervals on the ship side to reduce panting, the inward and outward deformation of side plating caused by the changes in water pressure.
5. Panting beams are normally spaced at every other frame space to absorb the transverse fluctuating forces induced during slamming and pounding of the ship. Channel bars are normally used as panting beams. Panting beams are also sometimes supported by pillars.
6. Perforated bulkhead (also known as swash bulkhead or wash bulkhead) refers to the centerline bulkhead which is not watertight. Its main function is to reduce free surface effect or heeling moments of water in tanks, which are not fully filled.
7. Perforated flat (also called perforated deck) is a horizontal deck which is non watertight. It acts as a kind of a full panting stringer to absorb the transverse forces. The deck is supported by panting beams and longitudinal girders like a usual deck The perforations on the deck are to facilitate the flow of liquid in the fore peak tank and also for man entry.
8. Solid floors are fitted at every frame spacing to reinforce the ship's bottom. A centerline girder is normally fitted to provide for rigidity of the structure with the transverse floors.
9. Collision bulkhead is mandatory and to be fitted at aft of the fore peak tank at a distance of 5 to 7.5% length of the ship from forward perpendicular.
1. Stem plate or stem bar or a combination of both in the forward most structure, which forms the profile of the bow. The stern plate is normally made of steel plate and is stiffened by a center line girder or stiffener. The stem runs from the highest point at the forecastle to the keel of the ship.
2. Breast hooks are fitted at intervals to stiffen the stem plate and to connect the stem plate to the panting stringers or side stringers.
3. Deck head is the uppermost deck of the fore peak tank which Is watertight. Entry to the fore peak tank is through man holes which are kept watertight by covers when ship is under way.
4. Panting stringers or side stringers are fitted at regular intervals on the ship side to reduce panting, the inward and outward deformation of side plating caused by the changes in water pressure.
5. Panting beams are normally spaced at every other frame space to absorb the transverse fluctuating forces induced during slamming and pounding of the ship. Channel bars are normally used as panting beams. Panting beams are also sometimes supported by pillars.
6. Perforated bulkhead (also known as swash bulkhead or wash bulkhead) refers to the centerline bulkhead which is not watertight. Its main function is to reduce free surface effect or heeling moments of water in tanks, which are not fully filled.
7. Perforated flat (also called perforated deck) is a horizontal deck which is non watertight. It acts as a kind of a full panting stringer to absorb the transverse forces. The deck is supported by panting beams and longitudinal girders like a usual deck The perforations on the deck are to facilitate the flow of liquid in the fore peak tank and also for man entry.
8. Solid floors are fitted at every frame spacing to reinforce the ship's bottom. A centerline girder is normally fitted to provide for rigidity of the structure with the transverse floors.
9. Collision bulkhead is mandatory and to be fitted at aft of the fore peak tank at a distance of 5 to 7.5% length of the ship from forward perpendicular.
Arrangements to resist panting
The structure of the ship is strengthened to resist the effects of panting from 15% of the ship's length from forward to the stem and aft of the after peak bulkhead.
In the fore peak, side stringers are fitted to the shell at intervals of 2m below the lowest deck. No edge stiffening is required as long as the stringer is connected to the shell, a welded connection being used in modern ships.
The side stringers meet at the fore end, while In many ships a horizontal stringer is fitted to the collision bulkhead in line with each shell stringer. This forms a ring round the tank and supports the bulkhead stiffeners.
The structure Is strengthened to resist the effects of pounding from the collision bulkhead to 25% of the ship's length from forward.
The flat bottom shell plating adjacent to the keel on each side of the ship is increased in thickness by between 15% and 30% depending upon the length of the ship, larger ships having smaller Increases.
In addition to increasing the plating, the unsupported panels of plating are reduced in size. In transversely framed ships the frame spacing in this region Is 700 mm compared with 750 mm to 900 mm amidships.
Longitudinal girders are fitted 2.2 m apart, extending vertically from the shell to the tank top, while intermediate half-height girders are fitted to the shell, reducing the unsupported width to 1.1 m.
Solid floors are fitted at every frame space and are attached to the bottom shell by continuous welding.
In the fore peak, side stringers are fitted to the shell at intervals of 2m below the lowest deck. No edge stiffening is required as long as the stringer is connected to the shell, a welded connection being used in modern ships.
The side stringers meet at the fore end, while In many ships a horizontal stringer is fitted to the collision bulkhead in line with each shell stringer. This forms a ring round the tank and supports the bulkhead stiffeners.
The structure Is strengthened to resist the effects of pounding from the collision bulkhead to 25% of the ship's length from forward.
The flat bottom shell plating adjacent to the keel on each side of the ship is increased in thickness by between 15% and 30% depending upon the length of the ship, larger ships having smaller Increases.
In addition to increasing the plating, the unsupported panels of plating are reduced in size. In transversely framed ships the frame spacing in this region Is 700 mm compared with 750 mm to 900 mm amidships.
Longitudinal girders are fitted 2.2 m apart, extending vertically from the shell to the tank top, while intermediate half-height girders are fitted to the shell, reducing the unsupported width to 1.1 m.
Solid floors are fitted at every frame space and are attached to the bottom shell by continuous welding.
Title-VIII After end arrangements
Title-IX Structures of different Ships
Midship section of bulk carrier
Cellular container ship
A cellular vessel is a container ship specially designed for the efficient storage of freight containers one on top of other with vertical bracings at the four corners. The majority of vessels operated by maritime carriers are fully cellular ships.Before 1991 most container ships were constructed with hatch covers. Because of the longer loading and unloading times of these types of ships, the cellular type was invented. As loading and unloading occurs only vertically and the containers have standardized dimensions (TEU), large quantities of cargo can quickly be loaded using gantry cranes.
Advantages:
(a) The cargo handling is more efficient resulting in shorter time in port
(b) Guide rails hold the containers into place instead of time-consuming lashings
(c) No need of hatch covers, reducing maintenance, weight, and handling
(d) There is a high freeboard, resulting in a stronger construction
(e) Containers lashed to cellular vessels are less vulnerable to crew tampering than containers on mixed-use cargo vessels, making them less of a risk from the standpoint of port security.
Disadvantages:
(a) The high freeboard results in higher registered tonnage
(b)The price of the ship is high due to the amount of steel used and the complex design process
(c) The absence of hatch covers means that rain water and overcoming seawater can freely enter into the cargo hold. Therefore, higher requirements of bilge systems are applicable to open cargo holds
Title-X Out fits & Deck Machineries
Anchor and Chain
Q.1 with reference to the ships anchor cable arrangement using simple sketches, illustration how each of the following are attached to the ship.(a) Cable Stopper;
(b) Anchor windlass;
(c) Chain locker end of cable clench.
Answer: a) Cable Stopper:-
When the anchor and its cables are fully heaved up and housed in
their place, i.e while the ship is riding at anchor, then a cable
stopper fitted in forecastles in line with the run of anchor chain also
called a devil's claw is dropped on to the chain so that the claws sit
inside the chain link and prevents it from moving. Thus the entire load
is taken up by the stopper and the windlass is freed from any shock or
vibration arising out of sea current, drag etc.
The cable stopper consist of heavy hinged stopper bar with a pointed edge which falls with in the chain link to hold the chain in place. The stopper is mounted on a frame with a roller on which the chain passes over. It is welded on to the deck with heavy insert plate, additionally stiffened by brackets.
b) Anchor Windlass:-
Anchor windlass is the lifting device for the anchor cable and is also used for mooring and winch duties. It consists of a barrel with specially shaped wildcat 'snugs' which the cable links fit into and pass round before dropping into the chain locker via the spurling pipe.
The hawse pipe is fitted to enable a smooth run of the anchor cable to the windlass and to maintain the water tight integrity of the forecastle. It should be of ample size to pass the cable which is snagging when raising or lowering the anchor the anchor. construction is usually of thick plating which is attached to a doubling plate at the forecastle deck and a reinforced stake of plating at the side shell. A rubbing or chaffing ring is also fitted at the ship's hull at the entry to hawse pipe for protection against anchor hitting. A sliding plate cover is shaped to fit over the cable and close the opening of hawse pipe when the ship is at sea.
c) Chain locker end of cable clench:-
The chain locker is normally fitted forward of the collision bulkhead and of adequate dimension to house all the anchor cable. it should be as low as practicable to reduce the height of the center of gravity of the considerable mass of the cables.
The chain locker is suitable is situated below the forecastle deck underneath the windlass. The chain links enter the locker through a spurling pipe adequately strengthen by heavy plate. solid round bar at the lower edge of the brackets.
The final link of the anchor cable is secured to the ship's structure by a clench pin. The pin can be raised by turning a hand wheel on forecastle deck. By releasing the clench pin, the entire cable can quickly pass out of the chain locker along with the anchor into the sea.
The cable stopper consist of heavy hinged stopper bar with a pointed edge which falls with in the chain link to hold the chain in place. The stopper is mounted on a frame with a roller on which the chain passes over. It is welded on to the deck with heavy insert plate, additionally stiffened by brackets.
b) Anchor Windlass:-
Anchor windlass is the lifting device for the anchor cable and is also used for mooring and winch duties. It consists of a barrel with specially shaped wildcat 'snugs' which the cable links fit into and pass round before dropping into the chain locker via the spurling pipe.
The hawse pipe is fitted to enable a smooth run of the anchor cable to the windlass and to maintain the water tight integrity of the forecastle. It should be of ample size to pass the cable which is snagging when raising or lowering the anchor the anchor. construction is usually of thick plating which is attached to a doubling plate at the forecastle deck and a reinforced stake of plating at the side shell. A rubbing or chaffing ring is also fitted at the ship's hull at the entry to hawse pipe for protection against anchor hitting. A sliding plate cover is shaped to fit over the cable and close the opening of hawse pipe when the ship is at sea.
c) Chain locker end of cable clench:-
The chain locker is normally fitted forward of the collision bulkhead and of adequate dimension to house all the anchor cable. it should be as low as practicable to reduce the height of the center of gravity of the considerable mass of the cables.
The chain locker is suitable is situated below the forecastle deck underneath the windlass. The chain links enter the locker through a spurling pipe adequately strengthen by heavy plate. solid round bar at the lower edge of the brackets.
The final link of the anchor cable is secured to the ship's structure by a clench pin. The pin can be raised by turning a hand wheel on forecastle deck. By releasing the clench pin, the entire cable can quickly pass out of the chain locker along with the anchor into the sea.
Q.2 Describe the procedure for testing, maintenance and survey of cables and associated gears.
Answer:- I. Test and maintenance
Before being accepted for service at sea all cable and associated gear are subjected to a proof load test; the proof loads of different sizes of forged steel cable are laid down by the Classification Society in the manufacturing specifications. In addition, samples of cable and associated gear are tested to destruction, in which the minimum breaking strength must not be less than 50 per cent above the proof load; for example, cable having a proof load of 100 tonnes must not fail under test below a stress of 150 tonnes.
The strength of cables may eventually decrease through wear, corrosion and fatigue, in the same way as the fittings. Fatigue is caused chiefly by the battering to which the cable is subjected when running out through the hawse pipe and the navel pipe, and when being hove in under strain. Cables are therefore surveyed periodically. The survey should bring to light any deterioration caused by wear or corrosion, and should detect any flaw or crack in a link caused by fatigue or misuse, but it will give no guide to the brittleness of the cable. The survey also provides an opportunity for rectifying minor defects, cleaning and overhauling joining shackles, and transposing the harder-worked lengths with others so that the whole cable will wear evenly. The periods at which survey and testing should take place depend on many factors, and are given in the Classification Society guidelines.
II. Procedure for survey
When berthed in a dry dock and embarking or disembarking cable, a dockyard slinger and a smith must be present, and work must be supervised by an experienced officer.
To prepare for a survey the cable lockers must first be cleared and the cable ranged (ie. laid out in fleets) on the floor of dry dock or deck or wherever convenient. If desired to range the cable along the bottom of a dry dock, permission must first be obtained from the General Manager of the dockyard.
Every shackle should be examined to ensure that the pin does not project, and should then be broken (ie parted). The machined surfaces should be cleaned and greased before reassembly, otherwise the shackles may become difficult to part. The various parts of different shackles are not interchangeable, because each shackle is made as one unit. The dovetail chamber of each shackle should be carefully reamed to remove every particle of the old lead pellet.
Lugged shackles and their bolts should be coated with soft grease, and their pins rubbed over with soft grease.
Every link and stud of chain cable is tapped with a hammer by a smith, to test it for a flaw, and Carefully examined. Should any link be found to have lost more than one-tenth of its original diameter (or one-eighth of the cable is smaller than 70 milli metres) from wear, corrosion or any other cause, the length of cable which includes the link is unfit for sea service and is to be returned to the dockyard, where the link will be replaced or the whole length condemned. A serviceable length is to be demanded,to replace any length which is condemned.
Swivels should be examined. The box-type are to be greased with a grease gun and the cups of the cup-type are to be filled with soft grease. All slips, adapter pieces and associated or spare gear are surveyed at the same time as the cable. The spare gear should be preserved by coating it with soft grease. Finally, the shackles of cable are transposed as required, to avoid undue wear on any one length, joined up together and re-marked. The inner end of the cable is then made fast to the cable clench in the locker and inspected by the Navigating Officer to confirm that it has been correctly secured; the cable is then stowed below.
Re-stowing cable:- With or without the assistance of a dockside crane, the cable should never be lowered directly down the navel pipe because it may acquire several unnoticed turns which will result in severe kinking and jamming of the cable when it is run out on the next occasion of anchoring. It must first be passed round the cable holder. If a crane is used, the cable is lowered on to the forecastle first. If no power is available the cable must still be passed round the cable holder and eased into the cable locker, using a tackle and joggle shackle. Whenever the movement of the cable is halted-for example, to connect the next length of cable-the brake should be applied and a pinch bar inserted through the link.
Balanced and unbalanced rudder
RuddersThe rudder is used to steer the ship. The turning action is largely dependent on the area of the rudder, which is usually of the order of one-sixtieth to one-seventieth of the length x depth of the ship. The ratio of the depth to width of a rudder is known as the aspect ratio and is usually in the region of 2. Streamlined rudders of a double-plate construction are fitted to all modem ships and are further described by the arrangement about their axis.
A rudder with all of its area aft of the turning axis is known as 'unbalanced'.
A rudder with a small part of its area forward of the turning axis is known as 'semi-balanced'.
When more than 25% of the rudder area is forward of the turning axis there is no torque on the rudder stock at certain angles and such an arrangement is therefore known as a 'balanced rudder'.
Construction of rudder
Modern rudders are constructed with steel plate sides welded to an internal webbed framework. Integral with the internal framework may be heavy forgings which form the gudgeons or bearing housings of the rudder. The upper face of the rudder's formed into a, usually, horizontal flat palm which acts as the coupling point for the rudder stock. A lifting hole is provided in the rudder to enable a vertical in-line lift of the rudder when it is being fitted or removed. A special lifting bar with eye plates is used to lift the rudder. A fashion or eddy plate can be seen at the forward edge on the unbalanced and semi-balanced rudders. This is welded in place after the rudder is fitted to provide a streamlined water flow into the rudder. After manufacture, every rudder is air tested to a pressure equivalent to a head of 2.45 m above the top of the rudder in order to ensure its watertight integrity. The internal surfaces are usually coated with bitumen, or some similar coating, to protect the metal should the plating leak. A drain hole is provided at the bottom of the rudder to check for water entry when the ship is examined in dry-dock.Windlass
Classification society rules governing windlass requires that :-
a) The windlass cable lifter brakes must be able to control the running anchor cable when the cable lifer is disconnected from the gearing while "letting go". average cable speed varies between 5 to 7.5m/sec during this operation.
b) The windlass must be capable of raising an anchor along with its chains from a depth of 82.5m to a depth of 27.5m ( 2 cable lengths) at a mean speed of not less than 9m/sec. if the depth of water is inadequate, a simulated condition can be considered.
c) The breaking effort obtained at the cable lifter must be at least equal to 40% of the breaking strength of the cable.
Although the test does not require both anchor to be lifted simultaneously, on a windlass fitted with two cable lifters, this is usually carried out and the time recorded. A visual check is made to ensure that the anchors stow correctly and that chain washing facilities are adequate.
Most anchor handling equipments incorporates one prime mover to drive two detachable cable lifters and also two wrapping ends for mooring purposes. when mooring light line speed up to 0.75 to 1m/s are required.
Name of chain drive?
Type of brake? Windlass overload in Hydraulic drive action what is slip clutch ?
Mooring or Wrapping drum purpose?
Safety feature in winches? type of crane operation?
Pressure vacuum breaker
They are fitted on every tanks for the purpose of preventing the tanks to get over pressurised or to come under vacuum, set to operate at 1900mmWG (0.186 bar) and negative 400mmWG(0.04 bar) pressure. Moderate pressure on large areas of cargo tanks causes damage either in form of Bulging or inward collapsing.Port hole and Deadlight
Q. What is porthole, what is deadlight. Requirement of deadlight, where fitted.Ans:- A strong shutter or plate fastened over a ship's porthole or cabin window in stormy weather.
Chapter part-I, Part B-2:- Openings in the shell plating below the bulkhead deck of passenger ship and the freeboard deck of cargo ships:-
1. The number of openings in the shell plating shall be reduced to the minimum compatible with the design and proper working of the ship.
2. The arrangement and efficiency of the means for closing any opening in the shell plating shall be consistent with its intended purpose and the position in which it is fitted and generally to the satisfaction of the Administration.
3.1. Subject to the requirement of the International Convention on load line in force, no side scuttle shall be fitted in such a position that its sill is below a line drawn parallel to the bulkhead deck at side and having its lowest point 2.5% of the breadth of the ship above the deepest subdivision draught, or 500mm, whichever is greater.
3.2. All side scuttles the sills of which are below the bulkhead deck of passenger ship and the freeboard deck of cargo ships, as permitted by paragraph 3.1, shall be of such construction as will effectively prevent any person opening them without the consent of the master of the ship.
4. Efficient hinged inside deadlights so arranged that they can be easily and effectively closed and secured watertight, shall be fitted to all side scuttles except that abaft one eighth of the ship's length from the forward perpendicular and above a line drawn parallel to the bulkhead deck at side and having its lowest point at height of 3.7m plus 2.5% of the breadth of the ship above the deepest subdivision draught, the deadlights may be portable in passenger accommodation, unless the deadlights are required by the load line convention to be permanently attached to their proper positions. Such portable deadlights shall be stowed adjacent to the side scuttles they surve.
5.1 No side scuttles shall be fitted in any spaces which are appropriated exclusively to the carriage of cargo.
5.2 side scuttles may, how ever be fitted in spaces appropriated alternatively to carriage of cargo or passengers, but they shall be of such construction as will effectively present any person opening them or their deadlights without the consent of the master.
6. Automatic ventilating side scuttles shall not be fitted in the shell plating below the bulkhead deck of passenger ships and the freeboard deck of cargo ships without the special sanction of the Administration.
Title-XI Dry Dock
Hull Inspection: In-water Survey
Preparation: To facilitate underwater survey, plans must be submitted showing the external features of the hull below the sheer strake with a key plan indicating the location of frames, bulkheads, weld lines, openings etc. In order that the survey can plan the action beforehand.
Cleaning: The hull plating surface is to be cleaned prior to the in-water survey by a particular system called 'Brush kart'. It is hydraulically operated vehicle with three brushing heads. It is drawn by a driver to clear the plating surface of all forms of marine fouling.
Survey Vehicle: It is a self propelled, steerable survey vehicle fitted with the following
(a) A long range low light TV camera to aid steering and check for hull distortion;
(b) A close view high resolution color TV Camera, to give a true picture of the state of the vessel coating and for inspections of weld seams;
(c) A 35mm still camera;
(d) An ultrasonic probe to measure plate thickness;
(e) A depth meter;
(f) Speed indicator;
(g) An umbilical cable from survey vehicle to survey Boat for electrical power supply to hydraulic motor and information transfer;
(h) Buoyancy spares and compressed air bottle for floating of the vehicle.
Survey Boat: It Houses the surveyor and consists of-
(a) A control containing TV monitors;
(b) Plate thickness print-out;
(c) Audio cassette recorder;
(d) Video cassette recorder;
(e) Play back unit;
(f) Drive communication system;
(g) Vehicle control system and all associated instruments.
Operation:
(a) The survey vehicle is taken to the datum line by a drive;
(b) With the aid of TV monitors and using the shell expansion plan as a map, the vehicle may be guided, from control console, over the bottom and sides of the hull by following weld-runs and other features such as inlets and tank plugs. Pictures and navigational information are relayed back and video recorded along with plate thicknesses giving the surveyor and integrated visual record of all relevant information. The vehicle will also provide pictures of stern frame, rudder, propeller, bilge, keels and hull openings.
(c) Drivers are also used for measurement of stern bearing wear down, pintle clearance and to inspect stern seals, anodes and rudder stock palm coupling bolts.
(d) The video recording, audio recording of the conversation between the surveyor and the driver and thickness printout and analyzed to obtain a clear knowledge of the ship's underwater condition.
Conditions and Requirements:
(a) This may be carried out for vessel having self-polishing paint in under water hull.
(b) The hull plating surface is to be cleared prior to the in-water survey by a particular system called "Brush kart". It is hydraulically operated vehicle with three brushing heads. It is drawn by a diver to clear the plating surface of all forms of marine fouling.
(c) To be carried out under water surveillance of a surveyor with.
(d) Ship is to be brought to suitable draught.
(e) Ship to be anchored possibly in sheltered water
(f) The water should be so choosen where visibility is good.
(g) The survey may be carried in lieu of any one of the two dockings required in a 5-year period on ships less than 15 years old.
(h) Beam of vessel to be greater than 30m (or less as agreed in special areas) and
List of items:
(a) Underwater hull up to load water line;
(b) Bottom and side shell for damages;
(c) Shell opening edges inspected for damage/wastage and corners for possible cracks;
(d) Condition of oil seal for stern tube;
(e) Rope guard, condition of propeller blades;
(f) Sea tubes;
(g) Sea water inlet and outlet valves;
(h) Sea chest grating;
(i) Sacrificed anodes;
(j) Compressed air, steam pipe lines to sea chest;
(k) Forward part of vessel for chaffing with chain, damage, with anchor including those on bulbous bow;
(l) Condition of bilge keel, possible cracks;
(l) Condition of bilge keel, possible cracks;
(m) Boot topping region for rubbing against quays and floating debris (region b/w ballast and loaded WL);
(n) Tank drain plugs for dents.
.
Title-XII Ship Construction Steps
Ans:- Ship construction Steps
A. Preliminary design is drawn up by a naval architect as per the owner requirements.
The points to be considered while drawing a preliminary design are:
The dimensions and displacement of the vessel.
Strength and stability of the vessel,
Propulsion,
General arrangement,
Classification society regulations,
Special features.
B. Contract design
Once the above factors are decided a fuller design can be prepared which is known as a contract design. This design can be circulated to various shipyards through tenders and quotations obtained for construction of the ship.
C. The sequence of events:
Ship design,
Drawing of plans – sheer plan, body plan, half breadth plan.
Approval of plans,
Filling of plans,
Transfer of plan to plate,
Plate preparation,
Plates and sections,
Production of sub-assemblies and assemblies,
Fabrication of units,
Erection and welding,
Launching,
Trials, tests, and certification.
D. Sequence of erection
The backbone of all ships is the keel which is a longitudinal girder or beam at the bottom of the ship, extending from bow to stern. This is the first stage of construction of the ship and several regulations refer to the keel laid date, At the forward end of the ship is attached an upright or nearly upright stem which forms the front of the vessel, A similar stern post is usually set at the aft end of the keel, The ship is then given a series of symmetrically curved ribs or frames that run transversely and that are fastened to the keel at their centers,
At and near their centers on the bottom of the ship the frames are made considerably larger than at the sides and are known as floors, The frames are held in position by longitudinal stringers or clamps that run the full length of the ship and that is curved to conform with the shape of the hull,
Additional bracing is provided by beams extending across the width of the ship and fastened at either end to the opposite sides of the ribs, In single deck vessels, only one set of beams is used while in multi deck vessels the number of sets of beams corresponds to the number of decks, The skin of the vessel is mounted outside the frame, The skin is in the form of a number of plates welded to the frames, these are known as strakes, The transverse bulkheads of metal plate run from side to side at several places in the length of the vessel, these bulkheads stiffen the frame and divide the ship into watertight bulkheads.
Erection sequence in general starts from bottom to top and from aft to forward in the following sequence:
Double bottom tanks,
Transverse bulkheads,
Side shell with frames,
Wing tanks,
Deck units with girder,
Accommodation modules,
Deck fittings,
Wiring,
Final painting.
E. Lines plan
The form of the ship can be determined by passing a set of parallel planes through the hull at regular intervals and measuring the outlines of these planes. The plan that defines the form of the ship by use of such planes is known as the “lines plan”
(a) When the planes are vertical and parallel to the centreline, a sheer plan is obtained which is a side view of the ship,
(b) When the planes are vertical and perpendicular to the centreline, a body plan is obtained which is an end view of the ship,
(c) When the planes are horizontal and parallel to the waterline, a half breadth plan is obtained which is a bird’s eye view of the ship.
Ship construction Steps
How ship is made? definition of deck plating? deck line?Ans:- Ship construction Steps
A. Preliminary design is drawn up by a naval architect as per the owner requirements.
The points to be considered while drawing a preliminary design are:
The dimensions and displacement of the vessel.
Strength and stability of the vessel,
Propulsion,
General arrangement,
Classification society regulations,
Special features.
B. Contract design
Once the above factors are decided a fuller design can be prepared which is known as a contract design. This design can be circulated to various shipyards through tenders and quotations obtained for construction of the ship.
C. The sequence of events:
Ship design,
Drawing of plans – sheer plan, body plan, half breadth plan.
Approval of plans,
Filling of plans,
Transfer of plan to plate,
Plate preparation,
Plates and sections,
Production of sub-assemblies and assemblies,
Fabrication of units,
Erection and welding,
Launching,
Trials, tests, and certification.
D. Sequence of erection
The backbone of all ships is the keel which is a longitudinal girder or beam at the bottom of the ship, extending from bow to stern. This is the first stage of construction of the ship and several regulations refer to the keel laid date, At the forward end of the ship is attached an upright or nearly upright stem which forms the front of the vessel, A similar stern post is usually set at the aft end of the keel, The ship is then given a series of symmetrically curved ribs or frames that run transversely and that are fastened to the keel at their centers,
At and near their centers on the bottom of the ship the frames are made considerably larger than at the sides and are known as floors, The frames are held in position by longitudinal stringers or clamps that run the full length of the ship and that is curved to conform with the shape of the hull,
Additional bracing is provided by beams extending across the width of the ship and fastened at either end to the opposite sides of the ribs, In single deck vessels, only one set of beams is used while in multi deck vessels the number of sets of beams corresponds to the number of decks, The skin of the vessel is mounted outside the frame, The skin is in the form of a number of plates welded to the frames, these are known as strakes, The transverse bulkheads of metal plate run from side to side at several places in the length of the vessel, these bulkheads stiffen the frame and divide the ship into watertight bulkheads.
Erection sequence in general starts from bottom to top and from aft to forward in the following sequence:
Double bottom tanks,
Transverse bulkheads,
Side shell with frames,
Wing tanks,
Deck units with girder,
Accommodation modules,
Deck fittings,
Wiring,
Final painting.
E. Lines plan
The form of the ship can be determined by passing a set of parallel planes through the hull at regular intervals and measuring the outlines of these planes. The plan that defines the form of the ship by use of such planes is known as the “lines plan”
(a) When the planes are vertical and parallel to the centreline, a sheer plan is obtained which is a side view of the ship,
(b) When the planes are vertical and perpendicular to the centreline, a body plan is obtained which is an end view of the ship,
(c) When the planes are horizontal and parallel to the waterline, a half breadth plan is obtained which is a bird’s eye view of the ship.
Q. What is modular construction?
Answer: Incorporation of modular construction technology in ship building reduces build period and also the overall cost of the project. In modular construction method, large moveable sections are constructed individually and then welded together. This method requires great accuracy in the manufacture of the units, but at the same time, reduces construction time by a factor of almost 10..
Title-XIII Questions and Answers
Questions and Answers
Question
1: Explain with sketches the terms hogging and sagging. Which structural members are affected to these conditions? State the type of stresses these members are subjected to under conditions.
Question
2: A. List SIX hazards that arise with the carriage of liquefied gas in
bulk.
B. Describe, with the aid of a sketch, the details of construction of
a prismatic cargo tank within a gas carrier designed to carry liquefied
gas(LPG).
Question
3: Describe a method of the attachment of bilge keels; State THREE
reasons for not extending bilge keels the entire length of the vessel;
Explain TWO principles of roll damping those bilge keels exploit.
Question
4: Draw and Describe the construction of a fore peak tank. Explain How
are the effects of panting and pounding taken care with help of neat
sketches?
Question 5: Discuss the need for adequate support of engine room gantry cranes, detailing the following:
(a) Sketch section through the engine room casing showing how the crane is supported by the ship structure;
(b)
State what restricts the forward and aft limits of the crane and what
is fitted to prevent the crane damaging the forward and aft bulkheads or
casing.
(c) State the Second Engineer’s responsibilities for the engine room gantry crane.
Question
6: (a) Considering the vessel as a compound beam define Bending moment
shearing force. Which is the point of Maximum Bending Moment?
(b) Sketch and Describe Hatch coaming of a large bulk carrier.
Question 7: A. Define the purpose of cofferdams,
B. State where cofferdams are most likely to be found on:(i) Dry cargo ships; (ii) Oil tankers.
C.
(i) State what information is available about danger of entering void
spaces. (ii) Identify, with reasons, the precaution to be observed
before and during entry to cofferdams.
Question 8: Describe the arrangement of tank top and double bottom in the machinery space making particular reference to the structure and scantlings below the main engine. Show the method adopted in the arrangement of D.B. tanks to avoid contamination of fresh water, fuel oil and lube oil stored in D.B. tanks.
Question 9: With the help of sketches explain the different types of strakes used in ship construction. What material is generally used for Hull plating and What are the tests carried out on Hull steel plating for certification as per class rules.
Question 10: With the aid of sketches, Explain various lines plan.
Question 11: The Hull of a vessel in way of the purifier room requires extensive welding repairs and as Chief Engineer you are requested to supervise.
A. Suggest a suitable type of welding process.
B. State, With reasons, FOUR common welding defects.
C. State what tests may be carried out for the hull repair before returning the vessel to service.
Question 12: With reference to the underwater surface of a ship’s hull;
A. Describe a hull plate roughness analyser system;
B. State the significance of the roughness profile and compare the typical roughness values for a new ship and a ship eight years old;
With reference to the application of self-polishing paint in dry dock –
C. Describe the plate preparation necessary;
D. State the defects that may occur in the paint coating if it is not correctly applied.
A. Describe a hull plate roughness analyser system;
B. State the significance of the roughness profile and compare the typical roughness values for a new ship and a ship eight years old;
With reference to the application of self-polishing paint in dry dock –
C. Describe the plate preparation necessary;
D. State the defects that may occur in the paint coating if it is not correctly applied.
Question
13: Describe a forced ventilation system for the machinery spaces and a
natural ventilation system for a lower hold. Why hold ventilation is
considered necessary?
Question 14: With reference to the prevention of hull corrosion discusses:
A. Surface preparation and painting of new ship plates.
B. Design of the ships structure and its maintenance.
C. Catholic protection by sacrificial anodes, of the internal and external areas of the ship.
Question 15: A rudder of a vessel requires extensive welding repairs and as a Chief Engineer you are requested to supervise ;
A. Suggest a suitable type of welding process;
B. State with reasons FOUR common welding defects that can occur there;
C. State what tests may be carried out before returning the rudder to service.
Question 16: With reference to International Load Line Statutory Certification,
A. State the reasons for the freeboard requirements;
B. Explain the term conditions of assignments
C. List the items that may be examined during a related survey after major repairs in the drydock.
D. Using a diagram indicate the freeboard of Type A, Type B, Type B60 and Type B100 vessels giving an example of EACH type.
A. State the reasons for the freeboard requirements;
B. Explain the term conditions of assignments
C. List the items that may be examined during a related survey after major repairs in the drydock.
D. Using a diagram indicate the freeboard of Type A, Type B, Type B60 and Type B100 vessels giving an example of EACH type.
Question 17: With reference to fatigue of engineering components:
A. Explain the influence of stress level and cyclical frequency on expected operating life;
B. Explain the influence of material defects on the safe operating life of an engineering component;
C.
State the factors which influence the possibility of fatigue cracking
of a bedplate transverse girder and explain how the risk of such
cracking can be minimized.
Question 18: With reference to Underwater Inspection in Lieu of Dry docking
A. Explain in detail, how an underwater survey is carried out;
B. State the requirements to be fulfilled before an underwater survey is acceptable to the surveying authority;
C. Construct a list of the items in order of importance that the underwater survey authority should include.
Question 19: Give a reasoned opinion as to the validity of the following assertions concerning ship structure:
A. Crack propagation in propeller shaft ‘A’ brackets or spectacles frames is indicative of inadequate scantlings and strength;
B. The adequate provision of freeing ports is as critical to seaworthiness as watertight integrity.
Question
20: The plane of the rudder of a vessel requires extensive welding repairs and as a Second Engineer you are requested to supervise –
A. Suggest a suitable type of welding process;
B. State with reasons FOUR common welding defects that can occur there;
C. State what tests may be carried out before returning the rudder to service.
Question 21: With reference to collision bulkhead explain the following using sketches as required:
A. Purposes of collision bulkhead.
B. Construction of collision bulkhead.
C. Regulations governing the position and construction of such a bulkhead.
Question
22: If a ship is seriously damaged under water in way of a large fuel side bunker tank what is the immediate effect and what may ultimately happen? What features in the ship would enhance safety on the vessel and marine environmental protection aspects in such a case?
Question 23: (a) Draw the mid ships section of an oil tanker with Double Hull & name each part.
(b) What is Bow Flare? Why is it so important in Bulk Carriers?
Question
24: Vessel has gone through very heavy weather. On arrival at safe
anchorage, you are conducting your inspection to determine damages to
hull.
A. List the areas you will inspect.
B. List your findings of any significance.
C. Write a report to company suggesting repairs if any.
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