Hi From this post you will deduce that one of my hobbies is sailing, I believe that applying a bit of science to the situation will improve my ability to make better tactical decisions on the spot. I have a GPS but am interested in getting a quick visual of boat speed related to the angle that the bow wave makes to the boat. Is there a simple relation between bow wave angle and boat speed? The type of hull that I am interested is a catamaran hull (long and thin) so it can never plane and the speed range I am interested in is about from 10 to 20 knots (~20 km/h to 40 km/h) Also I have heard in conversation that there is a maximum speed associated with a specific type of hull. (Hobie 16 catamaran for example) I would like to understand how this is determined, if it is at all possible. A hobie 16 hull does not have a centerboard like most hulls but is designed with an aerofoil shape. When one hull is flying (term used when one hull is raisd above the waterline), the other hull is in the water and the lift generates the stabalising influence (through hydrodynamic lift) that would normally be generated by a keel on a monohull. The hobie hull can be approximated by a long thin aerofoil dragged through the water in section. I think that there is a penalty incurred in the speed for this type of design, once again heard from somewhere. I would be interested to know what the lift and drag relations would be in relation to hull speed and how to determine them.