Naval Architecture and Ship Construction Archives - Page 17 of 19

Ship Hull Inspection

Dry docking is one of the best opportunity to carry out inspection of hull and other parts like propeller, rudder, etc. which are mostly under water.

Shell plating is inspected before cleaning, after cleaning and after painting. Following checks are carried out:

Check the condition of sea growth and shell plating
Check the amount of marine growth before cleaning to evaluate the effectiveness of anti-fouling paint
Check welds at the joint, after cleaning
Check condition of anodes. If anodes are fully corroded or consumed, that means either quality or quantity of the anodes used were insufficient and inadequate. If anodes are not at all corroded, that indicates improper fitting. Normally 75% of the anodes will be consumed.
Check the welded area for any cracks, corrosion or deformations
Check for buckling or corrosion of plates
Cracks are most common near welded areas. The possibility of cracks is more at the forward end (due to waves) and aft end (due to main engine and propeller induced vibrations)
Check for any twisting, damage or cracks on the bilge keel
Check damages to the bulbous bow

Check bulbous bow for indentation, bulging or cracks
Check for chain marking and impressions on it
Check for bow thruster tunnel and grating condition
If ship is more than 5 years old, surveyor may insist on gauging thickness of some portions on hull

Aft end requires very close examination since it is subjected to frequent vibrations slamming (impact loading)
Presence of different types of materials (for propeller, rudder, hull) may accelerate galvanic corrosion.
Check the Impressed Current Cathodic Protection (ICCP) and sacrificial anode conditions
Check the stern frame for cracks, bend, erosion, buckling, etc.

It consist of high and low sea chest, emergency sea chest, bow thruster tunnel, overboard openings, etc.

Inspect corrosion and condition of sea chest plating
Check sea chest grating
Inspect MGPS (Marine Growth Prevention System)
Check for steam injection and vent valves in sea chest
Gauging of sea chest plating for old ships
Check overboard valve connections to sea chest
Boiler blow down valves require more attention since it is subjected to high temperature, pressure, corrosion and erosion
Overboard valves to be tested for leakage
Any repair carried out on shell to be inspected thoroughly

When ship enters dry dock and pumping out water, check water whether water is coming out from rudder or not. If yes, then rudder is breached.
Open the top and bottom plug and check any water inside.
Pressure test rudder at a water head of 2.46 meters.
If the rudder is badly pitted or ship is older, surveyor may insist on thickness gauging of the rudder plate.
Check the sacrificial anode condition on the rudder.
Check the cement on coupling bolts for rudder and rudder stock. Remove the cement and check condition of the palm nut.
Check the rudder pintle clearance.
Check the rudder jumping clearance.
Check the rudder drop.
Carry out hammer test by surveyor’s hammer, by tapping on the rudder to evaluate the plate condition.
Check the actual position or true position of the rudder, compared to rudder angle indicator and see whether any difference is there by bending or deformations
Carry out a visual inspection.

Check oil leakage from stern tube.
Cut off the rope guard and check any fouling by fishing nets or ropes.
Propeller removed and inspected after alternate dry docks.
If stern tube is oil cooled, remove propeller every 5 years.
Inspect blade surfaces for erosion, pitting, blade surfaces, corrosion and bending.
Take measurements of propeller and compare with last records.
Take propeller drop.
Check stern tube condition for leakages.
For CPP (Controllable Pitch Propeller), check for blade movements and zero pitch settings with respect to wheel house. Check hydraulic oil leakages. Check securing arrangements for blades and carrier.
Inspect propeller for cavitation damages.