Hi Gert,

You may be absolutely correct about turning radius decreasing with a speed increase on the surface. I can remember operating a small fast boat in San Diego bay a number of years back and finding that making radical turns at high speed where the water was just about to the top of the gunwale but that I had so much side slippage that those kind of turns may have been tighter, but were actually much slower than making more moderate high speed turns. Remember the craft you are referring to is strictly a surface vessel and may also apply to a submarine that is also on the surface when most of the hull is above the water and turning in air, but submerged you have the force of water applied to the upper portion of the hull and control tower which is not present on the surface, and therefore its turns are against a much more substantial force due to the pressure increase on the yaw, pitch and roll axes.

Ron