Ch. 18 Flashcards
When a vessel goes aground what forces must be overcome to refloat it?
The resistance of ground effect (the weight of the vessel resting on the bottom) times the coefficient of friction on the bottom and the effect of wind, current, and heavy seas.
What procedures are used to refloat a vessel?
- Wait for a high tide to float the vessel
- Discharge ballast or fuel
- Discharge cargo into lighters
- Pull vessel off with tugs
- Heave vessel off with beach gear
- Jettison some of the cargo
Which is the least desirable method?
Jettisoning the cargo is considered to be the last resort since the vessel’s cargo is sacrificed to save the ship.
What are the first steps to be taken after a vessel goes aground?
The vessel’s draft should be checked to see how much buoyancy it has lost; sounding should be taken around the perimeter of the ship side to determine what portion of the hull is aground; and the bilges should be sounded to determine if the vessel is holed.
If a vessel is holed should it be refloated?
Only if there are enough pumps or compressors to keep it afloat.
What is one of the effects of current?
The buildup of sand or mud around a vessel that will make refloating it difficult.
What effects can heavy seas have on a vessel aground?
They can force a vessel farthur aground and make salvage operations difficult. Conversely, they can also help refloat a vessel by breaking the bottom suction or grinding down soft coral and limestone bottoms.
What should a vessel do to avoid being washed farther aground?
Lead out its anchors to restrain it, or ballast it down until the seas subside or assistance arrives.
If the vessel can refloat itself, why is it sometimes prudent to use a tug?
The vessel may require assistance steering to avoid broaching when it is refloated.
How may a small tug assist a ship that is aground?
A small tug can take a strain on the ship that will prevent it from broaching or “ Climbing the beach” until more assistance arrives.
What is beach gear?
“Beach gear” consists of heavy wire rope falls that are set up by a winch. They are attached to a heavy cable that is in turn attached to a shot or two of heavy chain and an anchor (usually an eell anchor) which is spotted offshore of the stranded vessel. This gear was often set up on the ship’s deck or on a barge attached to the ship, but modern salvage tugs are sometimes equipped to place the anchors and are attached to the ship by their own tow cable.
Are tugs sometimes more effective than beach gear?
Yes, since they can apply their force from several different directions and “swing” the ship back and forth while beach gear can only pull in one static direction.
To what type of emergencies might a tug have to respond?
To assist in beaching a vessel that has been holed, remove a burning tanker from an oil dock, breast a listing ship to the dock, and assist a vessel that has lost power or steering
How should a tug take a ship in tow that is on fire?
First, the tug should have its own crew in fire-fighting gear or oilskins and have its hoses lead out and ready to provide some protection to the tug’s crew. Then, the tug should back down and connect its towing gear to the vessel’s fire warps and take the vessel easily in tow after streaming about 250 feet of towline or cable.
Can one tug control the ship?
Usually, but the vessel will have a tendency to sheer away from the tug. It will be more easily controlled if there is another tug on a towline or pushing at the other end if the ship.
