A proa or prau (also seen as prahu) is a type of multihull sailing vessel. While the word proa just means boat in its native language, the term proa in Western languages has come to describe a vessel consisting of two (usually) unequal length parallel hulls. It is sailed so that one hull is kept to windward, and the other to leeward, so that it needs to reverse direction when tacking.
The proa is found in various forms primarily in the Malay Archipelago and the South Pacific, with the most well known examples from the Mariana Islands. Traditional proas superficially resemble outrigger canoes, with a buoyant lee hull and a denser, ballasted hull to windward for stability.
The defining feature of a proa is that the vessel switches directions when it changes tacks (stern becomes the bow and vice versa), always keeping the same hull to windward for ballast. This operation is referred to as "shunting". The main hull, or vaka, is usually longer than the windward hull, or ama. Crossbeams called akas connect the vaka to the ama. Traditional proa hulls are markedly asymmetrical along their length, and often curved in such a way as to produce lift to counteract the lateral forces of the wind. Modern proa hulls are often symmetrical, and use leeboards for lateral resistance.