Marine Engineering Study Materials

Details of Checks on Dry Dock Jobs

1. After the propeller has been satisfactorily fitted and the hydraulic nut properly tightened check that the bores on the propeller hub and on the hydraulic nut used for the hydraulic hose connectors have been sealed with gaskets and screwed plugs and that the plug heads on the propeller hub are locked by punch marks.
2. Check that the locking of the propeller nut has been done as per design.
3. Check that the propeller cap has been properly fitted with gasket and secured. Ensure that the void space in the cap has been filled with grease or tallow, as per Shipyard practice. The recesses on the cap for the securing bolts have to be filled with cement to provide a smooth streamlined surface.
4. After the aft seal housing and its liner have been properly secured, ensure that the bolt heads are locked either by the washers or by stainless steel wire locking two bolt heads at a time. The same is to be checked for the forward  seal housing also.
5. A concentricity check of the aft seal liner with the propeller shaft by dial gauge and a concentricity check of the aft seal housing with the liner by wedge gauge have to be carried out, as recommended by the seal Maker.
6. After oil has been filled in the stern tube, a tightness check of the oil seal rings in the forward and aft seal housings have to be carried out over a period of about 12 hours. Since the permanent oil piping for the stern tube lube oil system will not have been installed at the time of launching, a temporary plastic hose is usually rigged and filled up to the oil level normally maintained in the top header tank to provide the necessary pressure head.
7. Finally the wear-down gauge readings (top & bottom) at the aft seal have to be taken and recorded. Since there might be some eccentricity between the seal liner and shaft, to avoid error because of this it is necessary that ‘wear-down’ measurements are taken with the liner in the same position as when the reading was taken first time. For this reason it is necessary to identify the position by a mark on the propeller shaft flange in ‘top’ position.
8. Before fitting the wear-down gauge, ensure that no copper washer is left in the hole and also that the hold bottom is clean. After fitting the gauge and tightening it in the normal manner, a mark should be made on the seal housing in line with the mark on the gauge to ensure that the gauge is tightened to the same extent as at the first time in the building dock.
9. Check that the rope guard is properly welded to the stern boss and that the rope cutter knives are fitted as per supplier’s instructions.
10. If the condition of the propeller blades is not in ‘as manufactured’ condition, it is normal for the Shipyard to have the propeller polished and coated with varnish so that it is maintained in a clean condition thereafter.
11. The clearances in the rudder stock guide bush and pintle bush and rudder jumping clearance have to be checked.
12. If an Impressed Current Cathodic Protection system has been provided, it is necessary to ensure that the epoxy shield around the anodes has been correctly done. An insulation test has to be carried out for the anodes as per Makers instructions.
13. Besides the ICCP system, zinc anodes are provided at the stern area and on the rudder blade, in sea chests and in the tunnel for the bow thruster, if provided. Their condition should be checked and if any anode found wasted, they should be renewed. It is not advisable to fit anodes on the stern-tube boss immediately ford. of the propeller because of the turbulence they will create in the water flow to the propeller. All such anodes are masked before the final coats of anti-fouling are applied and it is important to ensure that the masking is removed before launching.
14. An inspection of all sea chests has to be made before the grids are closed. The vent and drain holes should be clear and all outfitting inside done as per drawings. The zinc anodes and MGPS anodes, if fitted, should be clean and without any paint.
15. If the ship has a BIS notation, the grids will be of the hinged type. Check that the grids swing easily and that the material of hinge pins, and securing bolts or studs/nuts are of stainless steel. After the grids are secured the locking of the bolts has to be confirmed. If locking wire is used it should also be of stainless steel.

Paint DFT (Dry Film Thickness) Check

Just prior to flooding the Shipyard QC dept. together with the Paint supplier’s inspector will carry out a ‘dft’ (Dry Film Thickness) check of the exterior hull, over flat bottom and vertical bottom area covered by anti-fouling paint. A ‘roughness check’ is also carried out at the same time. Ship’s officers may participate in these checks.