Semi-displacement Vessel

A vessel whose hull operates with substantial buoyant displacement support while also developing dynamic lift at higher speeds.

Semi-displacement forms can exceed the practical speed range of a comparable pure displacement hull without achieving the low immersed volume and lift-dominated condition of a full planing craft. They often have flatter after sections, moderate length-to-beam ratios and power suited to their intended transition range.

The label has no single universal numerical boundary. Resistance, trim, wake, fuel use and seaworthiness depend on hull form, loading, power and sea state, so semi-displacement should not be treated as automatically efficient in both displacement and planing modes.