Squat

Vessels operating in shallow canals all suffer from a phenomenon called squat. When a vessel travels through water she pushes water ahead of her.  In order for there not to be a ‘hole’ left in the water it must return down the sides and under the keel of the craft. As the space under and to either side is restricted there is an acceleration in flow velocity between the hull and the solid boundary of the canal. The smaller this space, the higher the velocity. (Bernoulli effect). This results in a drop in pressure and causes the vessel to assume deeper draft than that occurring when stationary. This is called ‘squat’. Vessels with full form such as canal boats when static running trim is zero will end up trimmed by the head. However zero trim is almost unknown fro most narrow boats - they are inevitable trimmed by the stern.

We have examined the squat characteristics of existing ‘traditional’ hull forms and compared them to the Floating Ohm hull form and deduced that there is little difference in the squat amplitudes for equivalent hulls. In the event the Floating Ohm hull performs slightly better with marginally reduced squat.