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THE Top Tip – Three of Hearts – Grounding Operations

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Getting cargo on and off of a vessel may be achieved in many different ways. If the cargo is already in the water and floating, then semi-submersible vessels may be employed that sink down, position themselves under the cargo, then de-ballast to rise up and transfer the load onto their deck. When completed the floating cargo is then high and dry on the back deck of the transport vessel.

The safe execution of this type of operation is reliant on many factors such as deck loading, cribbing and support placement, marine operations and securing for onward transport. The most critical and fundamental factor to a successful operation however, is ensuring the stability of the vessel is within allowable tolerances at every stage.

This stability is affected by many factors such as the geometry of the vessel and of the cargo when afloat and separate as well as the geometry when combined. It also is affected by whether the submerging vessel carries out the operation fully afloat and in deep water or if it grounds (touches) down to the seabed during the operation.

Touching the vessel stern down on the seabed can significantly increase the stability of the system as in this case you are not solely relying on the buoyancy and waterplane inertia to resist capsize. Rather you have the equivalent of a three-point support with the buoyancy of the vessel at the point of the triangle and the grounding forces (usually in way of the skegs) as the two points on the base.