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Grounding (Refloating by Salvage Experts)

(Please read my previous art on grounding calculations)

In my last articles on grounding I dealt with simple formulae in respect of pinnacle grounding and I also talked about refloating with limited resources. Sometimes, it may be felt that refloating by limited means is not possible in near future. The spring tides is far away and vessel is not secured well wrt. coast line, etc. Sometimes, a good salvage company may be readily available and the best choice is to refloat at earliest as the tidal journey has already commenced from springs towards neaps. Salvage experts would also be needed in case of damaged or foundered vessel.  A salvge company when approached, may need a variety of information, which would be provided by the ship.

The following information would be important in order to decide upon further action:

The salvage plan defines various works to be done including:

The idea being the dates and time stipulated in the project can be complied with. A good salvage plan should also consider the following:

Buoyancy Balloons

Pumping
The vessel cannot be under more than 10.00 meters of water, as building cofferdams for depths greater than this would be difficult and costly, due to pressures imposed to the same.

Compressed Air
This method is the fastest for the removal of a small size vessel from the bottom. The organisation of a salvage operation with the use of compressed air requires experience by the person responsible so that it is done successfully.

The use of compressed air in refloating operations requires that any patching or repairs done to the hull of the vessel are complete and waterproof, which is not required for pumping operations. Extensive work is necessary by the divers, whether for patching the hull or stabilising the craft, and this type of work can be expensive, in terms of material, labor and time. Stability calculations required during the de-watering operation using compressed air is an important consideration.

Lifting
This method requires a lot of seamanship with cables and tackles. The size of the ship to be saved is directly related to the lifting capacity available on the market.

The largest floating crane in operation probably is of a capacity to lift 14,000 tonnes when using it’s booms in yoyo. Handy sizes available are of the order 3000t.

Tug pull
For the success of a rescue operation on the high seas, the following requirements are basic:

  1. Tugboat, with suitable equipment and crew.
  2. Crew must be well versed with navigation especially the towed voyage.

Underwater Rapid Attachment
Steel plate patches, wooden patches, security bolts, lifting bolts, spinter boxes, cofferdams, salvage bolting, submarine bolt driving gun, etc. are available.

Submarine gun is an explosively actuated gun, which instantaneously and without previous preparation of the plate drives at high velocity, special steel alloy threaded bolts into steel plate up to 1 inch thick. The bolt is of special 100-tonne tensile steel with shearing strength of 10 tonnes per bolt. The lengthy and costly business of drilling, threading and bolting by normal methods is replaced by this most effective process. Bolts can be immediately and rigidly secured in the structure with strengths considerably in excess of the mild steel bolts usually employed. Bolts are available for wide variety of applications viz. threaded bolts, punch bolt, hollow bolts, etc. These are of heat-treated alloy steel of tensile strength of 90 tonnes per square inch. Bolting strengths are considerably in excess of those obtained with the usual mild steel bolts.

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