What is the depth at which shallow water effect will start feeling, start being felt? It will be more than if I move to the same ship at low speed. Do you understand what I am saying? I have got a speed which I am moving at fifteen knots. A ship moving at fifteen knots and I have got say thirty meters of water depth. It may not be important at that water depth, but if I move that same ship at twenty, twenty, knots, then the water depth effect will be felt.