Interaction at Sea

Extract

Dr Corlett's paper on hydrodynamic interaction (Journal, 32, No. 2, May 1979) is of great interest, coming as it does from a practising naval architect with considerable experience of dealing with complex issues arising from casualty investigations. His paper gives an insight into the causes of interaction and the practical illustrations given in the paper add weight to his arguments.

Model experiments to study interaction between ships in shallow water have been undertaken at the National Maritime Institute for some years now and many of the results obtained agree with conclusions reached by Dr Corlett. For example experiments carried out with models close to sloping surface-piercing and flooded banks have shown that at moderate to high speeds the side forces and turning moments induced by the banks vary not as the square of the speed, but as the speed raised to a power greater than two. It is of interest to note that the rudder force used to counteract these bank effects varies roughly as the square of the speed, so that when close to a bank at too high a speed, use of the rudder is less likely to maintain control than would be the case at a more moderate speed.

The author correctly emphasizes the advantages of a ‘kick ahead’ with a single screw ship, but it is well to bear in mind that this device is not applicable to some ships, notably those with twin-screws and a single centreline rudder.