Park Avenue boom

Park Avenue boom, a main boom, first fitted to the American J-class yacht Enterprise, which successfully defended the America's Cup in 1930. The conception of the yacht designer Starling Burgess, it was triangular in section, 1.2 metres (4 ft) at its widest point with a wide flat top—so wide that two men could walk abreast along it, hence its name—and was fitted with a series of lateral rails about 46 centimetres (18 in.) apart along its length. Metal slides were sewn along the foot of the mainsail which fitted these transverse rails, and stops, which limited the movement of the slides, were fitted into holes on the rails. These stops allowed the foot of the sail, or roach, to take up a gentle curve to obtain a better aerodynamic flow as the wind passed across the sail. To identify quickly the best positions for the stops in different sailing conditions, each line of holes was painted a different colour. These lines were called after the similarly coloured ones on the map of the New York subway system that marked the Seventh Avenue, Times Square shuttle, and Lexington Avenue subway lines.

The idea of such a boom was not entirely novel, as Dr Manfred Curry had written articles about its use in small boats, but it was the first time such a boom had been fitted to a large yacht. It was later used on other J-class yachts including Endeavour, the 1934 challenger for the America's Cup, and versions of it are still used in large yachts.