The 5O5 is a double-handed boat that incorporates a light weight, high performance hull design with a powerful sail plan and one trapeze. The boat is unique in that it has outstanding performance in all conditions. In light air it is quick and responsive, and in breeze it just goes faster. Planing begins in 10 knots of wind.

The Class Rules are One-Design, with the emphasis on controlling aspects that most directly affect boat speed. The sailplan and hull shape are tightly controlled, while the rigging layout, spars, and the foils are open. This allows the boat to be set up in many ways to suit the sailors; there are several distinct types of sail and layout combinations from the US, Australia and Europe. The result is that, at any Worlds, all the types will be used by the top 10 finishers, and usually by the top 5. Most US boats currently have adjustable shrouds, forestay, and mast ram, which allows rig tension, rake and bend to be changed while racing. There are many ways to rig the boat; it still takes the best sailors to win.

Hulls are built of either fibreglass/polyester or of epoxy resin/Kevlar and honeycomb composite. Both types are equally competitive when new, but twelve year old epoxy composite boats can still win major championships.

The ideal sailing weight varies with the prevailing local conditions, but most successful racers have a combined weight near 155 kilograms. The boat is difficult to sail in breeze with under 140 kilograms and few teams are over 180 kilograms. Two boats with women skippers have won North American titles.

The 505 class was started in 1954 when the French Yachting Association decided to establish a new One-Design racing class. The boat was designed by John Westell of Britain. The rules for the hull shape and sailplan have not been changed.

Active fleets abound throughout the US and Canada, Europe, U.K., Australia plus many other countries and regions