How about a thread on fast or semi-displacement trawlers

[eyschulman]

Well here I go. I think it is of value to classify a hull by its lines but maybe more important by how it runs in the water. Examples; a boat with planning hull lines is powered and used only below its rule of thumb theoretical hull speed. So to me that is a functional full displacement boat. Then take the same boat and put more power in it so it can exceed its hull speed but not to the point of lifting any significant part of the hull out of the water and the bow wave stays right on the bow. Now that boat for me is in a SD mode and may never truly plane and if slowed down can also travel in a full displacement mode. Next add more power and since the hull lines are planning capable the hull starts lifting out of the water and the bow wave moves back away from the bow till on extreme plane only the props are in the water as seen on very fast outboards. Some boats can transition from one mode to another with the planning hull capable of all three. Some designs by hull and power are more limited in their mode with the FD fixed at one mode and the SD two modes. There is usually a price to pay for using a boat out of its hull design parameters and that can be efficiency or handling characteristics or both. With care a boat designed to function in the SD mode can be a reasonable compromise for many and that is why there are so many of this type. Unfortunately the SD group suffers from excessive weight beam freeboard air height and broad bow entries all things that add to the happiness of she who must be obeyed.