Displacement hull speeds are largely determined by the length of a boat, but there is another factor....In my tender I have noticed that sitting my passenger further forward improves speed through the water for any given throttle on the motor. This it simply because the boat sits flatter in the water. As you accelerate the front of a displacement boat rises and the rear "digs in". The more throttle the bigger the angle and produced bow wave, which is of course wasted energy. Here is where it gets interesting. I have noticed with Serenity, having only my front mast and split junk sail means that all the forward force on the boat, via the mast, is trying to pivot the whole boat forwards. This has the effect of reducing the "dig in effect" and means Serenity sails flatter in the water. It also means that my bow wave under sail seems smaller than it was before. Less bow wave means the angle of the boat is also reduced. It is that angle which is largely the reason why longer like for like hulls have a higher design speed. I have noticed that all my longer trips on Serenity have been between 20 and 25% faster than when she was a cat ketch. Yes I have more sail area, but just adding more power on its own doesn't radically change the speed in water that the hull was designed for. Under motor Serenity performs exactly the same as before the conversion. Under sail she is truly a wonderful boat to handle. Has anyone else noticed this after conversion?