COURSE OF ACTION WHEN SHIP IS IN HEAVY SEAS
If a ship is operating in heavy seas following are the course of actions which should be taken:-
1) FREQUENTLY SOUND ALL HOLD BILGES:-
If a ship is operating in heavy seas, there is more likelihood of structural damage to the hull, hatch covers, ventilators, etc. due to green seas. This could allow water ingress into the hold and there will be an increase in mean draft. In addition, if the center of buoyancy of the intact volume after bilging does not lie in the same transverse plane as the center of gravity, there will a change in trim. And if the bilge space is asymmetrical with respect to center line of the ship, the ship will heel till the center of buoyancy of the intact waterline volume lies in the same fore and aft plane as the center of gravity. If the metacentric height GM in the flooded condition becomes negative, the resulting moment will cause the vessel to heel to the angle of loll, even though the bilged space is symmetrical with respect to center line.
The result of heel and trim may also result in further entry of sea water through non watertight openings which would further aggravate the situation, by causing loss of stability by flooding and free surface effect. So, frequent sounding of bilge space give an indication of any such damage.
2) FREQUENTLY SOUND BILGE IN CHAIN LOCKER, FORE AND AFT PEAK TANKS, COFFERDAMS AND OTHER VOID SPACES:-
Checking and sounding bilges in chain locker, fore and aft peak tanks, cofferdams and other void spaces for water ingress will indicate any structural damage affecting water tight integrity. The effect of stability will be same as described above. Also if the structural damage will be in chain locker and fore peak tank, it will cause the vessel to trim by head, with more green seas being taken at forward aggravating the problem.
3) SOUND ALL FUEL, FRESH WATER AND BALLAST TANKS:-
All the above tanks should be checked for again water tight integrity of ship and particularly fuel tanks and fresh water tanks for sea water contamination. Fuel oil contamination with sea water would increase the amount of water and sodium content in the fuel oil. The presence of sodium is determined for main engine, when sodium to vanadium ratio increases more than 1:3, this could lead to main engine component failure due to hot corrosion with serious consequences. Fresh water contamination would lead to water shortage on board. Flooding of ballast tank will affect the stability of the vessel due to free surface effect and unbalanced moments. So, sounding of above tanks is important for vessel safety.
4) IF SATISFIED WITH 1), 2), AND 3) TRIM SHIP BY STERN AND CORRECT ANY LIST:-
generally even keel is the desirable sailing condition, but in heavy seas if a trim by stern is maintained particularly in ballast condition, then there would be less likelihood of propeller/ rudder emerging out of water. Thus propeller racing and engine load fluctuation is avoided giving better power and steering. A trim by head would cause more green seas to be taken over the bows making the condition worse. Any list would reduce the roll angle necessary for deck immersion, hence any list should be corrected.
5) REDUCE SPEED OF MAIN ENGINE:-
Heavy pitching can cause main engine to be overloaded at the same speed. So, speed of main engine should be reduced. Also, reduction in main engine speed would lower the effect of green seas and thus reduce the possible structural damage, particularly at fore end. Ship motion ( rolling, pitching etc.) would generally be better and the change in speed would cause a change in periodic time of wave encounter, which would reduce resonant motions and vibration if they had been occurring.
1) FREQUENTLY SOUND ALL HOLD BILGES:-
If a ship is operating in heavy seas, there is more likelihood of structural damage to the hull, hatch covers, ventilators, etc. due to green seas. This could allow water ingress into the hold and there will be an increase in mean draft. In addition, if the center of buoyancy of the intact volume after bilging does not lie in the same transverse plane as the center of gravity, there will a change in trim. And if the bilge space is asymmetrical with respect to center line of the ship, the ship will heel till the center of buoyancy of the intact waterline volume lies in the same fore and aft plane as the center of gravity. If the metacentric height GM in the flooded condition becomes negative, the resulting moment will cause the vessel to heel to the angle of loll, even though the bilged space is symmetrical with respect to center line.
The result of heel and trim may also result in further entry of sea water through non watertight openings which would further aggravate the situation, by causing loss of stability by flooding and free surface effect. So, frequent sounding of bilge space give an indication of any such damage.
2) FREQUENTLY SOUND BILGE IN CHAIN LOCKER, FORE AND AFT PEAK TANKS, COFFERDAMS AND OTHER VOID SPACES:-
Checking and sounding bilges in chain locker, fore and aft peak tanks, cofferdams and other void spaces for water ingress will indicate any structural damage affecting water tight integrity. The effect of stability will be same as described above. Also if the structural damage will be in chain locker and fore peak tank, it will cause the vessel to trim by head, with more green seas being taken at forward aggravating the problem.
3) SOUND ALL FUEL, FRESH WATER AND BALLAST TANKS:-
All the above tanks should be checked for again water tight integrity of ship and particularly fuel tanks and fresh water tanks for sea water contamination. Fuel oil contamination with sea water would increase the amount of water and sodium content in the fuel oil. The presence of sodium is determined for main engine, when sodium to vanadium ratio increases more than 1:3, this could lead to main engine component failure due to hot corrosion with serious consequences. Fresh water contamination would lead to water shortage on board. Flooding of ballast tank will affect the stability of the vessel due to free surface effect and unbalanced moments. So, sounding of above tanks is important for vessel safety.
4) IF SATISFIED WITH 1), 2), AND 3) TRIM SHIP BY STERN AND CORRECT ANY LIST:-
generally even keel is the desirable sailing condition, but in heavy seas if a trim by stern is maintained particularly in ballast condition, then there would be less likelihood of propeller/ rudder emerging out of water. Thus propeller racing and engine load fluctuation is avoided giving better power and steering. A trim by head would cause more green seas to be taken over the bows making the condition worse. Any list would reduce the roll angle necessary for deck immersion, hence any list should be corrected.
5) REDUCE SPEED OF MAIN ENGINE:-
Heavy pitching can cause main engine to be overloaded at the same speed. So, speed of main engine should be reduced. Also, reduction in main engine speed would lower the effect of green seas and thus reduce the possible structural damage, particularly at fore end. Ship motion ( rolling, pitching etc.) would generally be better and the change in speed would cause a change in periodic time of wave encounter, which would reduce resonant motions and vibration if they had been occurring.
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