1) As per M.S. cargo ship construction and survey rules (INDIA) 1991, every vessel has to dry dock twice in 5 years in which the intermediate dry dock should be at two and half years but can be extended up to 3 years. Intermediate dry dock can be replaced by in water survey but ship has to be dry docked at 5 years interval.
2) M.S. cargo ship construction and survey rules 1991 also states that propeller shaft and the tube shaft driving screw propellers shall be withdrawn and surveyed at intervals not exceeding two and half years, but Principal officer can extend it up to 3 years. However, depending upon the tail shaft system like oil bath or water bath, keyless propeller or keyed propeller, the survey requirement can be extended.
WHY DRYDOCKING IS A MAJOR EVENT:-
Drydocking is referred to as major event because of reason that without it the portion of ship can not be assessed. Following checks and repairs are carried out in dry dock:
1) Cleaning of ship’s hull and to check ship’s hull fouling condition.
2) See the condition of underwater hull painting and its requirement.
3) See the condition of underwater hull plating and requirement of its renewal.
4) To fulfill requirement of tail shaft survey.
5) For propeller and rudder inspection and repair.
6) To check and change the sacrificial anodes fitted in underwater area.
7) To see local deformation like bulging, sagging of ship hull and repair it.
8) To see bow thruster tunnel, inspect the tunnel and blades of thruster.
As drydocking is very important and costly affair it’s preplanning is required. As a chief engineer different steps to prepare the vessel for drydocking are:-
1) Drawing of steering gear, rudder, propeller, ship side valves, and gratings are to be studied and kept ready.
2) Last initial report to be checked regarding rudder drop, tail shaft, stern tube bearings, shaft seals, poker gauge reading, pintle clearance etc.
3) Inventory of spares
4) Inventory of stores
5) CSM items due
6) Identification of defect and preparation of defect list.
7) Requirement of any specialized service
8) Job allotment
9) Job timing schedule
11) Assess paint requirement with master
12) See last anchor chain report and prepare for inspection.