Also, the yacht can be controlled in reverse, which is seldom true of ordinary yachts. Twin keels become more effective with the angle of heel . Because twin keels cant outward at the tip, the leeward keel becomes more vertical and deeper in the water as the boat heels. Also, with this cant outward from the vertical, leeway forces water up to the root of the fin as opposed to spilling over the tip in a single keel. Hydrodynamic tests have shown that decreasing end tip loss can double the effectiveness of a fin - the sole purpose of keel winglets.
Twin keels improve speeds .
Part of the reason for this is the relatively small wetted surface which yields improved light air performance. Modern twin keels are of high aspect ratio and present less wetted area than a full keel or long fin keel, while at the same time, retaining the steady helm associated with full keels. Directional stability is markedly enhanced by the fins . This has been proven in tank tests and in full size yacht performance. Rudder areas are smaller for the same reason as the keels .