Deck machinery

Hatch Covers

Deck machineries routine maintenance

Rocking test of deck crane

Hatch Covers

Construction Material of Hatch covers:-

1. Mild Steel

Generally, Grade A mild steel is used for the construction of all cargo access equipment. Grade A is the ‘ordinary’ mild steel used for most ship building purposes.

Certain application requires Grades D and E steel. Grade D is notch-tough steel with a chemical composition largely chosen by the steel producer provided that it retains good weldability. Grade E steel is the highest grade and is also notch-tough but its manufacture and composition are strictly controlled. Grades D and E steel are specified for coaming bars on refrigerated ships where low temperature brittle fracture must be guarded against. As these steels have low corrosion resistances, special coating, e.g. epoxies, are often used on the underside of hatch covers where sweating can cause accelerated corrosion. Other materials such as higher tensile steel and aluminium are acceptable to the Classification Societies.

2. Higher Tensile Steel (HTS)

If the stress level within a structure were the only factor governing its scantlings, the use of higher tensile steel instead of mild steel would result in weight savings of up to 15 percent. However stress is not the only governing factor. Deflection, minimum thickness, ease of construction, initial and maintenance costs must all be taken into account. Higher tensile steel (HTS) can sometimes be used for the beams of hatch covers, with their top plates made from mild steel. This reduces the weight of the covers, without incurring the extra cost of using all HTS construction. Thus, HTS is sometimes used on hatch covers where, by reducing the cover weight slightly, it may be possible to install less powerful operating mechanism. Construction entirely in HTS is sometimes used in pontoon covers for container ships, to keep their weight below the maximum lifting capacity of container cranes.

3 Aluminium

Aluminium structures can be 55-60 percent lighter than equivalent mild steel structures. Most of the problems associated with higher tensile steel are not present with aluminium. Since it is not as strong as steel, thickness have to be increased, thereby alleviating problems associated with minimum regulatory deflection, buckling etc., unless the design is such that deflection is significant. Welding aluminium does however require special skills and equipment. Corrosion is less of a problem if the

correct grade of material is used and if precaution are taken where steel and aluminium meet, e.g. at coamings. The spacing of stiffeners can be increased in an aluminium structures this has the added advantage that the number of stiffeners and hence the weight and cost of the structure can be further reduced. The major disadvantage of aluminium is that a suitable grade of material for access equipment costs approximately eight times as much per tonne as mild steel, with the overall

effect of increasing the cost of the cover by upto three times. Aluminium covers have been fitted to deep tanks because they are so much lighter. Since deep tank covers are often made in one piece, aluminium covers are easier to handle without power assistance. Aluminium single pull weather deck covers have occasionally been fitted in the past, sometimes experimentally. Aluminium can be used for Ro-Ro vessel access equipment but it is usually limited to small ramps and car decks. It is less resistant to fire damage than steel.

4. Glass Reinforced Plastic (GRP)

GRP structures are light but the modulus of elasticity of GRP is only 7 percentages of that of mid steel and excessive deflection is a problem which invariably accompanies its use. Additional stiffening is thus necessary, making the structure heavier and more expensive to manufacturer. For this reason GRP has not as yet found wide application in the construction of cargo access equipment, although development work is in progress. GRP in ‘sandwich’ construction could be particularly suitable for covers in refrigerated ships because insulation can be built into them during the manufacturing process at very little extra cost, whereas the present system of insulating steel covers

is expensive and time consuming.

Design requirements for hatch covers:-

1 Hatch Covers

The hatch cover structure consists in essence of steel beams or grinders spanning the shorter hatchway dimension, plated over on top completed by steel side and end plates. The top plate provides the top flange of the beams and grinders. For the simpler types of hatch cover panel, e.g. pontoon or single pull, the design and analysis assume a uniformly loaded simply supported beam.

Structural regulations

The construction of exposed hatch covers is governed by regulations 14 to 16 of the 1966 Load line convention (1966 LLC). Regulation stipulates that exposed coamings and hatchway covers above the superstructure deck shall comply with the requirements of the appropriate national administration, which means in effect, that such equipment's must be design in accordance with the current practice of the administration.

A. Cleats

The 1966 LLC requires that satisfactory means for securing weather tightness be provided, and gives requirements for covers secured by tarpaulins and battens. For gasket covers, details are usually agreed between the hatch cover designer and classification society.

An important aspect of the gasket type securing arrangement, whatever its form is that the pressure between the sealing gaskets and compression bars is correctly maintained. Manual cleats are often over tightened despite the steel to steel contact of the cover skirt plates on the coaming bar, with the result that gasket. Life is severely shortened. This problem is overcome by the introduction of resilient and quick acting cleats which means that the correct sealing pressure is consistently and uniformly applied. Cleats on steel covers are generally spaced about 1.5-2 m apart, closer

adjacent to the corners, and no more than 0.6 m apart for wooden covers. With the advent of larger and heavier hatch covers, the classification societies have, in some cases, approved covers with greater than usual cleat spacing.

B. Loads

The hatch loading laid down by the 1966 LLC, take account of the forces exerted on exposed covers by heavy seas breaking over the deck. Once again however, these are mandatory minimum values and the classification societies may require that they are increased in certain cases.

C. Scantling

Minimum scantling (thickness and dimensions of steel plating and stiffeners) and load factors for steel covers re-specified in the 1966 LLC, so that the load factor multiplied by the maximum stress in the covers is less than or equal to the minimum ultimate strength of the steel. Corresponding minimum scantling depending on loading are given in classification society rules, alternatively direct calculations of required structural strength may be made using maximum design stress levels.

The top plate of a typical hatch cover panel may be from 6-13 mm thick depending on the spacing of the beams (generally, thickness=spacing/100). This plate is stiffened by beams spanning the hatch cover, usually fabricated ‘tee’ beams having a depth of about 4 percentage of the span and spaced 500-1000 mm apart. The panel is completely by side and end plates which may be from 8.20 mm thick.

D. Deformation

As the ship become larger and hatchways take up a greater percentage of the deck area, so the question of hatchway deformation becomes more important. Traditionally ships have fairly small hatchways and so have derived a considerable amount of their strength from their decks. As hatchways have increased in width, so the deck’ contribution to the longitudinal and the torsional strength of the hull girder has declined, being limited to the strips of deck outboard of the coaming and between the hatches. A ship with hatchways more than 70 percentage of the beam in width has

approximately half the torsional rigidity of a similar ship with hatchways which are only 40 percentage of the ship’s beam. Compensation in the form of thickened plating and/or box girders may be required.

It has been suggested that, since hatchways are always closed by hatch covers, the latter ought to be designed to contribute to the strength of the hull girder. This is however not practical as the devices securing the cover to the coamings would have to be excessively robust, and any deformation due to the loading of the vessel in port could lead to the covers becoming jammed and thus impossible to open. Moreover, to make a significant contribution to vessel’s strength, the covers would have to be

considerably stronger and heavier than at present, and this could introduce operational difficulties.

Hatch coamings can be designed to contribute to the longitudinal strength of the ship but there can be problems associated with this. If it is decided to use the coaming in this way, they must be continuous over the midship portion of the ship and properly tapered at the forward and after into account in calculating the midship section modulus, according to classification society requirements.

Longitudinal deformation of the top of the coaming is due to the hogging or sagging of the vessel. It depends on hatchway length and may be as much as 7-8 mm at each end. Longitudinal deformation is compensated for by fitting at the ends of the hatch cover with wide gaskets whose rubber absorbs the relative movement of the compression bars as the sip works. Hatch end cleats must allow such movements, which would otherwise be taken up at the cross joint with attendant risk of leakage.

Steel to steel contact is must. The purpose of this is to prevent the over compression of the gaskets. However, it gives rise to a frictional force whose magnitude depends on the pressure of the cover on the coaming bar and their relative movement.

Transverse deformation is caused mainly due to the vessel’s changes in draft as cargo is worked, but also by hogging and sagging. Deformation of as much as 15-25 mm over the width of long hatchways is possible. Relative movement between the cover and the coaming is allowed for in a similar way to longitudinal deformation, by providing the cover with wide gaskets, and by ensuring that the wheels on one side of the hatch cover panels are free to move laterally as shown in fig 3.4

Torsional deformation is caused by the combination of non symmetrical loading of the vessel and hydrodynamic forces when the ship heads diagonally into waves. It can rack the midships hatchway diagonal of a large container ship by as much as 30 mm. By fitting resilient cleats at the ends of the

hatch covers, some movement between cover and coaming takes place, thus reducing the relative movement between panels.

2 Seals

The 1966 LLC requires cargo access openings to be weather tight which is generally achieved by an arrangement of sealing gaskets and drainage channels.

The main requirements of sealing system are as follows:

(i) It must prevent any transfer of water from outside the ship to the cargo space,

(ii) On combination carriers, it must be oil tight to prevent any transfer of liquid from the inside of a cargo space to the outside, when subjected to the pressures.

(iii) It must be able to maintain the weather tight integrity of the cargo space in all sea states and thus, it must be able to accommodate the deformation discussed earlier.

(iv) It should be resilient and able to accommodate normal irregularities in the mating surfaces,

(v) The gasket should be abrasion resistant as it may rub against the mating surface. It must also be resistant to cargo contact,

(vi) It should be easy to maintain,

(vii) It should retain all the above properties throughout a long service life, exposed to climate extremes.

A. Gaskets material:- Gaskets material must be of a suitable quality; it should not harden excessively when subjected to neither sub-zero temperature nor soften in tropical conditions.

Particularly important in this respect are gaskets fitted to refrigerated vessels. Most gaskets used for seals on dry cargo ships are of natural, synthetic or neoprene rubber, while combination carriers requires a nitrile composition, resistant to chemical attack by oil. In general neoprene synthetics have good heat, ageing, weather and flame resistance, but only moderate oil and chemical resistance but worse cold temperature properties. General construction of seal steel work, welding and painting

needs careful attention.

B. Compression bars:- The usual arrangement of compression bars is of rectangular section mild steel welded to the coaming bar. After several years of service, these bars can become badly corroded and require replacing. Moreover, they may then have sharp corners which press into the gaskets so that the rubber takes on a permanent set earlier in its life than would be the case for a sealing arrangement employing either a round compression bar, as shown or rectangular one with rounded corners. The latter produces an element of ‘knife edge’ loading which gives the good seal with the rubber. When such compression bars are fitted, they are often of stainless steel, which, although initially expensive, often worth while as it is not usually necessary to replace the bar during the life of the corners.

Types Of Hatch Cover:-

There are three common type of hatch covers on the basis of their operations:-

1. Portable or lift away type:- Independent covers are lifted by lifting tackle or spreader using cranes.

2. Rolling type.

3. Hydraulic folding type.

Rolling covers:-

In this type, cover will roll over the hatch coming track with rollers fitted on the hatch cover which will perform open /close operation.

They usually consist of two large panels at each hatchway. They are fitted with wheels which roll along a track at both sides of the coaming top. Stowage rails, which may be portable, extend this track via pillars welded to the deck. In some installation, the wheels are not attached to the hatch cover but to the coaming and to fixed pillars on the deck, and the cover rolls across them. Apart from stowage location, the principal difference between side end rolling covers is that the joint in between side rolling panels is longitudinally and between end rolling panels is athwatships. These covers are usually fitted to large ships. They are often extremely heavy owing to their large dimensions and require hydraulic pot lifts (rams) to raise them into the rolling position. These hydraulic lifts are fitted to the coaming below the wheels (in their closed position) and are illustrated in fig. There is no limit to the size of the covers, and panels 20 metres square (20 m x 20 m) have been installed in ships.

Folding covers

They may be fitted at both weather deck and tween deck hatchways. In its simplest form, this type of hatch cover consists of two flat topped panels.

A typical hydraulic operated cover is shown. Adjacent panels are hinged together so that they can be folded. The panel at the stowage end is hinged to a plinth welded to the deck and hydraulic rams are usually arranged as shown. The ram rod is withdrawn into the cylinder to prevent corrosion when the hatch is closed at sea. Covers up to 26 m wide have been installed in ships.

In many case cover consists of two folding pairs .One pair is stowed at the after end of the hatch and the other forward .The fold pair is operated by the hydraulic cylinders act directly on the end hinge arms which are connected at stools on the deck. When the cylinders push the end panel up from closed position the cover folded and the second panel is fitted with the wheels, rolls on the rails to the stowage position. The panels are usually secured in the open position by semi automatic hooks interact interacting with the wheel arms.

Water hose leak detection test:-

Water hose tests are used to determine weather-tightness of hatch covers. If correctly performed, hose testing will show hatch joints that leak. The general procedure for hose testing is to apply a powerful jet of water from a 20-50 mm diameter hose fitted with a 12 mm diameter nozzle held at a distance of 1-1.5 metres from a hatch joint, moving along the joint at a speed of 1 metre every 2 seconds.

The drawbacks of hose testing are: 

The hold needs to be empty; 

It cannot be performed in sub-zero conditions; 

It requires the deck scupper drains to be open (potentially causing pollution); 

The test cannot pinpoint leaks on the cross-joint or side joint accurately; 

Two people are needed to supervise the test.

Care should be taken to avoid excessive nozzle back-pressure.

Ultrasonic leak detection test:-

Ultrasonic leak detection is a viable alternative to the hose test for testing hatch covers, access doors and access hatches for weather tightness, as it accurately locates potential points of leakage. This test should only be carried out using class approved equipment and approved test proceduresThe test involves placing (with hatches closed and secure) an electronic signal generator inside the cargo hold. A sensor is then passed around the outside of all compression joints. Readings taken by the sensor indicate points of low compression or potential points of leakage. Ultrasonic testing overcomes the majority of limitations associated with hose testing and can be carried out when holds are loaded. The drawbacks of these section tests are: 

The equipment requires an experienced and specialist operator to interpret the readings. 

The equipment requires regular calibration; 

The equipment is not normally part of the ship’s equipment.

Chalk testing:-

When performing a chalk test, the top edge of every compression bar is covered with chalk. Hatches are then fully closed and reopened. The rubber packing is examined for a chalk mark, which should run continuously along the packing centre. Gaps in the chalk mark indicate lack of compression. Chalk testing merely indicates if hatch panels are aligned and compression achieved. It will not show whether compression is adequate and therefore it is not a test for weather tightness.

Hatch cover maintenance

Hatch covers require frequent inspection, de-rusting and regular maintenance. They are exposed to very harsh conditions, especially the salt-laden air, the frequent waves and contamination by cargo during loading/discharging. The time available for maintenance is also difficult to schedule, since it cannot be done when the hatches are loaded. with cargo, and also when loading / discharging is going on. Even when sailing in ballast, the time available depends to a large extent on good weather conditions, availability of man-power as also cost constraints.

The lack of proper maintenance causes a steady deterioration in performance, and the possibility of costly delays in port, when hatch covers are not able to be operated. This could also lead to other costs due to claims, port charges and so on.

The manual gives the routine maintenance due, which will include the greasing, care of wire ropes and other fittings, and the maintenance of the hydraulic or other system which operates them.

Rubber seals are normally expected to last for at least 4 to 5 years, but may fail due to neglect or damage by wrong operation, by painting over them or even by over-compression. If the seal channels are corroded, then this should be rectified, before trying to fit a new seal, which may not seat properly.

Usually the channels would need to be grit-blasted and coated with a zinc based coating, by an approved workshop, before fitting a new seal. The seal is cut to the required lengths keeping an additional allowance of about 3% to take care of shrinkage or unevenness.

Joints must be cut square and smooth, and glued on three sides. Sharp tools should never be used, which could damage the seal rubber. Pay particular attention to the corners, which are prone to leakage.

Minimum length of rubber insert to be 500 mm. When replacing the seal 'rubber, do so completely, since parts of old rubber may not match the thickness of the new one.

To take care of friction between the compression bar and the seal, a special grease is usually applied on the seal rubber. The compression bars to be chipped, ground and painted before fitting on a new seal, in order to preVent damage to the new seal from any rough surfaces.

Seal compression is to be measured and noted down, at the time of fitting of the new seal.

If any water should penetrate past the rubber seal there is system for draining the cross joints. There are usually secondary gulleys to guide any leaked water back to the deck.

This prevents any corrosion from taking place.

Surveys

An annual survey is done along withtle hull survey. A special survey is required at a maximum interval of 5year. This requires a hose test.

Deck Machineries Routine Maintenance 

abcd

I- Regular Checks:- 

Routine inspection of the winched is a very important from of preventive maintenance and will result in considerable savings by detecting any major trouble that might be developing, and allowing the necessary repairs to be made on a planned or normal shut down time, e.g at docking.

The following is a guide to some of  the key points which should be observed during routine inspections. The frequency at which the inspection should be made is depending on time and condition the winches have been in operation, how ever, it is recommended that the intervals listed below be considered maximum for optimum performance from the winches.

It is also recommended that inspections of the winched are made more frequently in the first period after the winches have been started up first time. 

Before each mooring operation:- 

 -Grease all gear teeth.

- Grease all plain bearings.

During mooring operation:-

- Grease main shaft bearing 4-6 hours.

-listen to bearings or abnormal noise and checks for overheating.

Once each week:-

- Grease all gear teeth.

- Grease all plain bearings.

Once each 3 month:-

-check the brake linings.

-check that all coupling are working properly.

-check all hydraulic piping and valves for leaks.

-check the hydraulic mototr foundation for proper tightness.

Once each year:-

-check the bearing clearances.

-check the gear wheel contact.

-check the end stoppers and see that the winch is not moving.

-check all bolts and nuts for proper tightness.

-check the condition of complete winch.

-check that the various hydraulic valve are correct adjusted.

Deck crane inspections and maintenance:-

Maintenance Schedule:

Weekly:

Grease nipples on winches, blocks, derricks cranes.

3 months:

Auxiliary equipment (chains, rings, hooks, swivels, blocks and shackles).

6 months:

A thorough overall check of the above equipment.

Grease nipples checked.

Derrick: stripped and all auxiliary equipment gear taken apart examined greased and reassembled.

Winches to be overhauled as part of the PMS

Location and identification number of each item complying with the rigging plan.

Each item to have a certificate.

12 months:

De-rust, paint and overhaul derrick goose necks

Deck Machinery maintenance
Deck machinery requires periodic inspection and maintenance, in order to get efficient operation. The harsh climatic conditions to which it is subjected in its exposed location, as compared to engine-room machinery, makes it very important to follow regular maintenance schedules, in order to avoid costly break-downs and inconvenience during cargo operations.
General items :
1. Grease all points on winches, blocks, cranes, hooks, shackles and so on weekly.
2. Every three months, carry out an inspection of ancillary equipment, such as chains, rings, hooks, swivels and blocks.
3. Regular overhaul to be done as per the PMS schedule or every 6 months, whichever is shorter.
4. SWL and identifying marks to be always visible.
5. The file containing the certificates should be examined, to ensure that all are valid.
6. Winches should be overhauled, especially the brakes, as per the PMS schedule or every 6 months, whichever is shorter.
7. Cranes and other lifting equipment to be de-rusted, overhauled and painted as per the PMS schedule or every 12 months, whichever is shorter..

Rocking test of deck crane

Rocking test is carried out to ascertain the wear down of the sleeve bearing of the deck cranes by measuring the play (relative movement) between the inner and outer bearing race. This measurement indicates the rate of wear. Slewing bearing is one of the most important components of deck crane, so It is very important to grasp the condition of slewing bearing periodically in order to prevent unexpected trouble.

Interval of the test is Every 6 month. If the class has other requirement of Rocking test interval, that should be followed. And if wear amount close to tolerance, more frequent inspection is required.

– The Rocking Test needs to be carried out according to manufacturer recommendation.

No loads shall be to the crane hook, positions below are usually marked and used always as a datum reference.

Measurements are typically taken in four positions on the slew bearing, with the jib pointing towards the fore side, starboard side, stem side, and port side.

Procedure of rocking test.

Fix the dial gauge on the outside surface of the fixed post, and apply the probe to the bottom surface of the outer ring of the slewing ring. (The measurement point is "measuring point -1" on the rear of the deck crane.)

If the measurement is performed inside the fixed post, place the dial gauge on the inside surface of the fixed post and apply the probe to the bottom surface of the base plate of the deck crane.

Perform the initial setting (direct the top of the jip upward.)  Direct the top of the jib upward by luffing operation. (Minimum reach) Adjust the dial gauge to zero.

Lower the jib to the maximum reach by luffing operation. Record the indicated value of the dial gauge at the measuring point of the rear side of the deck crane.

Check that the bottom surface of the pinion doesn’t contact with the top surface of the fixed post top flange.

Be sure to measure without load. If the wear volume is measured with load, the contact position between the ball of the bearing a raceway varies, the dial indicated value fluctuates greatly. Measure the wear volume at the 0 point position without slewing the deck crane.

Make a diagnosis of the measured result. The result of the measurement of step 3 is the wear volume including the clearance between the ball of the bearing and raceway. If any one of the results of the measurements towards 4 sides, the fore side, starboard side, stem side and port side, exceeds +3mm from the initial value (allowable wear volume), replace the bearing. The allowable wear volume is same regardless of outside measurement/inside measurement

Q. Continuous hatch coaming?

Q. Hatch coaming and hatch cover arrangement at mid ship section of a bulk carrier?

Q. Diagram of hatch stiffener? where and why used?

Q. Mooring arrangement and all parts of it?

Q. Overhead crane load test?