Thin or bulky: Optimal aspect ratios for ship hulls

Empirical data reveal a broad variety of hull shapes among the different ship categories. We present a minimal theoretical approach to address the problem of ship hull optimization. We show that optimal hull aspect ratios result - at given load and propulsive power - from a subtle balance among wave drag, pressure drag, and skin friction. Slender hulls are more favorable in terms of wave drag and pressure drag, while bulky hulls have a smaller wetted surface for a given immersed volume, thus reducing skin friction. We compare our theoretical results to real data and discuss discrepancies in the light of hull designer constraints, such as stability and maneuvrability.