Ship behaviour and control at low speed in layered fluids

Fluid mud layers on the bottom of navigational channels may affect a ship’s behaviour and control.Tests with self-propelled ship models navigating in a two-layer fluid system have shown the occurrence of an internal undulation system with characteristics depending on the ship's forward velocity.A simplified one-dimensional theory is developed for determining approximately the interface deformation and the ship's squat.Results of systematical model tem are discussed, Emphasis is laid on effectivity of propulsion and rudder manoeuvres. There are clear indications for instable rudder behaviour and poor propulsive efficiency if due to a combination of initial keel clearance (KC), squat effects and internal undulations, the ship's keel is in contact with both fluids. The theoretical developments lead to a practical estimation of the conditions in which controllability problems may occur