hullforms

Hullforms are the shapes of a ship’s hull that determine how it displaces water, carries loads, and moves through waves. The hull form governs buoyancy distribution, stability, draft, and propulsion efficiency, making it a central consideration in naval architecture throughout the design process.

Hullforms are commonly grouped by their primary operating regime: displacement hulls, planing hulls, and semi-displacement hulls. Displacement hulls are efficient at low to moderate speeds and carry loads with minimal power, while planing hulls rise partly out of the water at high speeds to reduce drag. Semi-displacement hulls blend these characteristics. In addition, hulls can be monohulls or multihulls (such as catamarans and trimarans), each offering different stability, interior volume, and hydrodynamic behavior.

Key descriptive parameters used to compare hullforms include the block coefficient (Cb), which relates the displacement volume to the product of length, beam, and draft; the prismatic coefficient (Cp), which links volume to the wetted length and waterplane area; and the waterplane coefficient (Cwp), which compares waterplane area to planform area. Designers also consider length between perpendiculars, waterline length, beam, and the overall underwater geometry, as these factors influence resistance, seakeeping, and maneuverability.

Modern hullform design relies on a combination of theoretical hydrodynamics, empirical data, towing-tank tests, and computational fluid dynamics. The goal is to balance speed, fuel efficiency, stability, and seakeeping, recognizing trade-offs between payload at low speed and performance at high speed. See also naval architecture, hydrodynamics, and vessel performance.