Answer MEP Question 30

Q. Describe a suitable means of withdrawal procedure for the removal of keyless propellers.

Pilgrim fitting of propeller

Propeller hub with sleeve:-

cast iron sleeve bonded into the propeller boss by using a special form of Araldite injected with pressure. C.I sleeve easier to handle to be bedded with taper shaft, machining and bedding than with a complete propeller.

Cast iron has a coefficient of friction nearer to the shaft.

Pilgrim Nut has an internal nitrile rubber tube, which when inflated hydraulically forces the steel loading ring against the propeller hub. Loading ring travel should not exceed 1/3rd of loading ring width, to avoid rapture of rubber tube.

Preparation before assembly:-

(a) propeller or sleeve must be bedded to its tail shaft and checked with blue marking. if sleeve, to be bonded into propeller boss.

(b) propeller and tail-shaft the wipe clean and dry.

 if cast steel propeller bosses, then light smear with clean oil.

(c) measure temperature of shaft and propeller hub. Determine from the pushup diagram, the push-up need depending on temperature.

(d) pilgrim nut and shaft thread should be liberally coated with "MolyGrease".

(e) Put the propeller on the tail shaft. Never jack the propeller by Loading ring.

Assembly:

(a) Mount pilgrim nut with loading ring on the tail shaft against propeller hub. The loading ring must flush with the face of the nut. Rotate the nut nearest position, so blanking plugs on top and bottom respectively.

(b) Connect the oil pipe at the bottom and keep the top plug open. Start the pump with clean oil, when bubble-free oil comes out from the top plug, then tighten it.

(c) Pump up until pressure gauge showing 1000psi;(67bar).

Make a reference mark on the shaft or liner 25mm forward end of the hub(initial mark). Also, fit a dial gauge to record the continuous travel as per rising pressure.

(d) vent loading ring, turn the nut so that the loading ring is flush with the force of the nut.

(e) pump up to the working pressure corresponding to boss and shaft temperature.

(f) Make a second 25mm mark (final mark), compare with a dial gauge.

(g) vent and remove the oil pipe and adaptor from the nut body.

(h) rotate the nut to force the loading ring "HOME", Fit the plug.

(i) Test with a feeler gauge between nut and propeller boss [no clearances]

(j) fit the locking plate.

(k) fill up with tallow, fit the fairwater cone and lock it in place.

Withdrawal:-

(a) Remove fair water cone and slacken off the flange ring to secure the rubber ring at the FWD end of the propeller boss or sleeve.

(b) clean the weight of the propeller and remove the locking plate.

(c) Take the weight of the propeller and secure it.

(d) Unscrew the pilgrim nut completely, reverse and screw back again, so that the loading ring will now be facing aft.

(e) assemble the withdrawal plate and secure it with studs and nuts.

(f) Insert a pair of the wooden blocks between propeller boss aft end and pilgrim nut.

(g) The free gap between the faces of wooden blocks and propeller boss aft end should not exceed 1.6mm more than the "push up" distance.

(h) Connect oil pipe at the bottom of pilgrim nut and keep top plug open. Start the pump with clean oil, when bubble-free oil comes out from the top plug, then tighten.

(i) Pump up the nut up to the required pressure, which can be obtained from the ship's record with respect to the temperature of the dry dock.

(j) Once the propeller jumps off, remove the oil pipes and adaptor.

(k) Screw down the hexagonal nuts securing the withdrawal plate. This will drive the loading ring back to zero or flush position.

(l) Remove the hexagonal nuts and withdrawal plate and studs.

(m) Tighten the blanking plug after ensuring the Dowty seal is correctly seated.

(n) The pilgrim nut and then propeller may be removed.

SKF or oil injection fitting

Preparation before assembly:-

(a) the propeller must be bedded to its tail shaft and checked with blue marking.

(b) clean inside propeller boss and shaft taper surface with acetone.

(c) Measure temperature of shaft and propeller boss.

(d) Determine from the push-up diagram the push up needed depending on temperature.

(e) Put the propeller on the shaft, adjust the circumferential position of the propeller boss with moly grease.

Assembly:-

(a) Fit oil jacks (if non-hydraulic nut), screw the nut on the shaft to the aft face of the boss up to specified torque. Rotate the nut/jack nearest position, so blanking plugs on top and bottom.

(b) Mount pump holder and pump. connect the oil pipe at the bottom and keep the top plug open.

Start the pump with clean oil, when bubble-free oil comes out from the top plug, then tighten it.

(c) Fit a dial gauge to record continuous travel as per rising pressure.

(d) Mount pump holder, increase oil pressure of nut/jacks only. Measure pushup load when push up distance is 0.5, 1.0, 1.5 &2.0mm.

(e) Decrease oil pressure of nut/jack gradually.

(f) Determine "zero point" by measurement.

(g) Reset dial gauge to record continuous travel as per rising pressure. Make also reference mark on shaft (depends on push up distance).

(h) operate all pumps. The pressure of the pump(nut/jack) should not exceed 500atm. The final pressure of the other pump should be of the order of 500 to 700 atm depends on temperature.

(i) Push up boss to designed push up distance corresponding to temperature.

(j) Make a second "reference mark" ( final marking)

compare with dial gauge should be the same as marking.

(k) After having reached the pushup (control by dial gauge) and confirmation from reference marking, release the interface pressure of the pump but maintain the pressure of the hydraulic nut/ jack for a further 15minutes to enable the oil film between shaft and propeller to disperse completely. At low temperature or when using higher viscosity oil the time should be longer. Fit back the plug on propeller boss.

(l) Remove oil pipes.

(m) Tighten up the nut against the boss. if jack, then it is to be removed and tighten the nut.

(n) Test with filler gauge between nut and propeller boss.

(o) No. clearance, Fit the locking plate

(p) Fill up with tallow, fit the fairwater cone and lock in place.

Withdrawl:-

(a) Remove fair water cone and slacken off the flange of simplex seal(chrome steel liner flange).

(b) Clean the area around the nut and remove the locking plate.

(c) Take the weight of the propeller and secure it.

(d) Loosen propeller nut and put a wooden piece between boss and nut. Keep the gap a little more than push up the distance.

(e) Fit oil pump and pressure gauge on propeller boss. Connect oil pipe at bottom of the boss and keep top plug open. Start the pump with clean specified hydraulic oil. When bubble free oil comes out from the top plug, then tighten it.

(f) Increase oil pressure of propeller boss interface gradually, wait until propeller comes free and slip back against the nut.

(g) The nut and then propeller may be removed.