Hidden Shapes Of Racing Hulls

Design of underside of an outboard racer's hull is key to speed, stability

Racers pick their hydroplane hulls according to shape of course they will run. At racing speed three-point hydro touches water only with propeller and pontoons at side of hull, gives fast ride on straightaway but is relatively unstable in choppy water and tends to skid on turns. Single-step hydro rises on after part of step in hull, offers more drag at high speeds but allows tighter maneuvering on turns by biting deeper into water. Racing runabout is souped-up version of conventional pleasure-boat, has unbroken hull lines and same stabilizing fin as single-step hydro. At slow speeds runabout behaves like any displacement boat; but as driver pours on power runabout rises out of water, planes on rear 1/3 of bottom at speeds up to 63.8 mph.