The Retractable Tri, says the maker Airmar, serves powerboats, cruising sailboats and racing sailboats. It requires only a 2-inch hole in the hull and is available in a choice of eight flush-mount housings of plastic, bronze or stainless steel. Airmar designed the Retractable Tri for use in water of 200 feet or less. Its fan-shape beam provides consistent tracking even when it's mounted on a bottom deadrise of 22 degrees or a heeling sailboat. Airmar Technology Corp., www.airmar.com.