oats are a mass of compromises. B A perfect example is the hull shape. The best shape for space optimisation at any given length would be a rectangular box. Of course that’s also the very worst shape for seakeeping. What you need to cleave waves offshore is the exact opposite, something as long, narrow and pointed as possible to reduce wave impact to a minimum. But as if that were not enough, our beleaguered naval architects have to consider hull form. A full displacement hull that sits fully immersed tends to give the best low-speed efficiency and seakeeping but is hampered by a low hull speed. As an example, a 30ft waterline length displacement hull tops out at about 7.5 knots. If you want speed, you’ll need a planing hull which creates dynamic lift with speed and skims across the top – great for velocity but not very comfortable in choppy conditions. But there is a third way. A semi-displacement hull gives enough lift to overcome displacement hull speed limitations but doesn’t skim over the top like a planing hull.
