Semi Displacement Hull

As the name suggests, these hulls fit neatly in between the displacement and the planing hull types. The stern of the semi-displacement hull is lower and designed to be always below the water. The hull can be round bilge form but is generally of the ‘Hard chine’ type. These hulls have less fullness than a full displacement hull.

The chine line runs aft with a small curve from where it enters the water and on back to the transom. The hull sections are designed with a moderate vee. The semi-displacement hull will out-perform the displacement ‘Hull Speed’ rules and will accept additional power to convert it to additional speed, however there are limits to this benefit.

Generally speaking, for vessels with 30ft / 9.1M to 60ft / 18.3M waterline length, you should only consider semi-displacement hulls if your speed requirements do not exceed 12 to 18 knots.