A proa or prau 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, 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 region known today as the Mariana Islands, and were first documented by Western explorers in the 16th century. Traditional proas superficially resemble outrigger canoes, with a buoyant lee hull, and a denser, ballasted hull to windward for stability.
The first documented proas made in the Western world appeared in the middle 19th century in Europe, ushering in a period of interest in the design. Western builders, working from the drawings and descriptions of explorers, often took liberties with the traditional designs, merging the native designs with Western boatbuilding methods, and often radically changing the layout, so that the only thing remaining in common with the traditional proa was the windward/leeward hull arrangement. The modern proa exists in a wide variety of forms, from traditional small proas still raced in the Marshall Islands, to high tech versions specifically designed for breaking speed sailing records.
The native names of the various components of the proa have also entered the jargon of sailing. The main hull of the proa is known as the vaka, the outrigger as the ama, and the outrigger supports as the akas. The terms vaka, ama, and aka have been adopted to describe the analogous parts in trimarans.
There are a number of other vessels that use a similar layout, with uneven hulls and a shunting sails, but are culturally and historically distinct from the proa. Examples of these are the Fijian Drua and the Melanesian Tepukei.
The crab-claw sail is something of an enigma. It has been demonstrated to produce very large amounts of lift when reaching, and overall seems superior to any other simple sail plan (this discounts the use of specialized sails such as spinnakers). C. A. Marchaj, a researcher who has experimented extensively with both modern rigs for racing sailboats and traditional sailing rigs from around the world, has done wind tunnel testing of scale models of crab-claw rigs. One popular, but disputed theory is that the crab claw wing works like a delta wing, and works by generating vortex lift. Since the crab claw does not lie symmetric to the airflow, like an aircraft delta wing, but rather lies with the lower spar nearly parallel to the water, the airflow is not symmetric. This can clearly be seen in Marchaj's wind tunnel photos published in Sail Performance: Techniques to Maximize Sail Power (ISBN 0-07-141310-3). The vortex on the top spar of the sail is much larger, covering most of the sail area, while the lower vortex is very small and stays close to the spar. Marchaj attributes the large lifting power of the sail to lift generated by the vortices, while others attribute the power to a favourable mix of aspect ratio, camber and (lack of) twist at this point of sail.
Vessels that have a bow at either end are found scattered throughout history, with the earliest mention being in Pliny the Elder's Natural History, where he describes double-ended vessels being used to transport cargo across the straight at Taprobane, or what is now the Palk Strait between India and Sri Lanka, where the double-ended nature of the vessels allowed them to ferry cargo back and forth without turning around.
The history of the Micronesian proa is not recorded until it was first encountered by European explorers when they first explored the Micronesian islands; the earliest written accounts are by Antonio Pigafetta, an Italian who was a passenger on Ferdinand Magellan's 1519—1522 circumnavigation. Pigafetta's account of the stop at approximately 146 E, 12 N, (the Mariana Islands, named the Ladrones by Magellan's men) describes the proa's outrigger layout, and ability to switch bow for stern, and also notes the proa's speed and maneuverability, saying And although the ships were under full sail, they passed between them and the small boats (fastened astern), very adroitly in those small boats of theirs. Pigafetta likened the proa to the Venetian fisolere, a narrow variety of gondola; this is an apt comparison due to both the long, thin shape and asymmetric nature of single-oar gondolas.
Lord Anson's 1740—1744 circumnavigation, completed in 1744, also encountered the proa. An example was captured by the fleet in 1742, and a detailed sketch of the proa was made by Lt. Peircy Brett of the HMS Centurion. Rev. Richard Walter, chaplain of the HMS Centurion, estimated the speed of the proa at twenty miles per hour (32 km/h). Since Pigafetta's account, though finished in 1525, was not fully published until the late 18th century, the accounts from Anson's voyage were the first exposure most Europeans had to the proa.
There is also a loose group of individuals from all over the world with an interest in the proa, both from a historical perspective and from a scientific and engineering perspective. Many of these individuals with interests in proas can be found in the Amateur Yacht Research Society.
There was a surge of interest in the proa in Europe and America in the late 1800s and early 1900s, which can be seen in the work of western builders like R. M. Munroe and Robert Barnwell Roosevelt (Theodore Roosevelt's uncle). The proa was, into the 20th century, one of the fastest sailing craft in existence. Indeed, the proa still forms the basis for the design of many boats involved in speed sailing.
Although proas are mentioned in Western publications in the mid 1800s, and there is some record of a copy built in 1860, the first well documented Western versions of the proa was built in 1898 by Commodore Ralph M. Munroe of the Biscayne Bay Yacht Club. Yacht-design giant Nathanael Herreshoff, a friend of Munroe, may have also had an interest in the project. There is a small model of the Anson-Brett proa at the Herreshoff Marine Museum in Rhode Island; who made it is uncertain.
Over the following years, Munroe built several more. They were all destroyed by the mid-1930s, when a severe hurricane leveled Munroe's bayside boatshop, but at least two of his designs were documented in articles in The Rudder, as was one by R. B. Roosevelt. Small proas may have been brought back to the United States in the late 1800s, but documentation is sparse. These seem to be the first two builders to attempt to adapt the proa to Western building techniques.
Since Munroe had no direct experience with proas, all he had to work with was the widely distributed and incorrect plan drawing from about 1742, made during Admiral Lord Anson's circumnavigation of the globe in search of Spanish treasure ships. This drawing had been circulated in the press, for example, in William Alden's articles in Harper's Magazine (his articles were reprinted in a small book called The Canoe and the Flying Proa This proa was one of several either captured or seen under sail when Anson stopped at Tinian during a Pacific crossing. One key element that Brett, the draftsman, misinterpreted was the mast, shown fixed vertically in the center of the boat. Traditional proa masts were raked end to end as the vessel shunted. A raking mast helps with helm balance by moving the center of effort of the sail fore and aft.
Munroe, however, was a talented boat designer who was able to work around the problems with the drawings, and his adaptations can be seen in successive proas. Rather than the deep, asymmetric hull of a traditional proa, Munroe's hulls were flat bottomed (similar to the fisolera referred to by Pigafetta), with keels or centerboards for lateral resistance. His first iteration had an iron center fin with a half-oval profile. Rather than the traditional crab-claw sail's spars which meet at the front, Munroe's sails used what could be described as a triangular lugsail or spritsail with a boom, similar to the modern lateen sail with a shorter upper spar.
Munroe's first proa was only 30 feet long, yet was capable of speeds which Munroe estimated at 18 knots. His article in The Rudder describes what can only be planing on the flat hull. As this was before the advent of planing power boats, this proa was one of the first boats capable of planing, which helped give it its amazing speed in the days when most boats were limited by hull speed. For example, a 30-foot boat that was not capable of planing would have a hull speed of about 7.3 knots; Munroe's proa could reach nearly 2.5 times that speed. This accomplishment was the nautical equivalent to the X-1 breaking the sound barrier. It is not clear that traditional proas of the Pacific islanders were ever capable of planing, though the long, slender hull would have a much higher speed/length ratio than other contemporary designs. Munroe was building a "cheap and dirty" sharpie hull made of two 32-foot planks, a couple bulkheads and a crossplanked bottom, and by lucky accident may have been the first sailor to plane his boat.
Roosevelt's short article is accompanied by photographs showing his proa Mary & Lamb, at rest and under sail. It is not clear if the boat predated Munroe's 1898 proa.
Since Munroe wasn't aware of the raking mast, his 1900 model used two daggerboards set fore and aft of the mast, which would allow adjustment of the center of lateral resistance to provide helm balance. From the drawings, it appears the mast is higher as well, allowing a larger sail. The sail design also changed, with the upper spar now being slightly longer than the upper edge of the sail, and projecting past the apex slightly to allow the apex to be attached to the hull. The sail was loose footed, with the boom attached to the upper spar near the sail apex, and to the clew of the sail. His article in a 1900 issue of The Rudder included more details on the construction of his second proa. A 1948 book of sailboat plans published by The Rudder includes the following specifications for the 1900 proa:
From the drawings, the distance from the center of the main hull to the center of the aka is about 12 feet.
For example, unconventional boat and yacht designer Phil Bolger has drawn at least three proa designs; the smallest one (20 ft) has been built by several people while the larger two, including his Proa 60, have not been built. For additional examples, see here.
The terms ama and aka have been adopted by the modern trimaran. Since trimarans are generally designed to sail with one ama out of the water, they are similar to an Atlantic proa, with the buoyant leeward ama providing the bulk of the stability for the long, relatively thin main hull. Some modern proa designers have returned the favor, and borrowed trimaran design elements for use in proas. Trimarans often have main hulls that are very narrow at the waterline, that then flare out and extend over a significant portion of the akas. This topheavy design is only practical in a multihull, and it has been adapted by some proa designers. One notable example are the designs of Russell Brown, a boating fittings maker who designed and built his first proa, Jzero, in the mid 1970s. He has created a number of proa designs, all of which follow the same theme.
One of the design elements that Brown used, and a number of other designers have copied, is the lee pod. The akas extend past the main hull and out to the lee side, and provide support for a cabin extending to the lee of the main hull. This is similar to the platform extending to the lee on some Micronesian proas. The lee pod serves two purposes—it can be used for bunk space or storage, and it provides additional buoyancy on the lee side to prevent a capsize should the boat heel too far. Crew can also be moved onto the lee pod to provide additional heeling force in light winds, allowing the ama to lift under circumstances when it would not otherwise. The Jzero also used water ballast in the ama to allow the righting moment to be significantly increased if needed. While Brown's proa was designed to be a cruising yacht, not a speed sailing boat, the 36-foot Jzero is capable of speeds of up to 21 knots.
One of the more practical rigs was invented by Euell Gibbons around 1950 for a small, single handed proa. This rig was a loose footed lateen sail hung from a centered mast. The sail was symmetric across the yard, and to shunt, what was previously the top end of the yard was lowered and became the bottom end, reversing the direction of the sail. Proa enthusiast Gary Dierking modified this design further, using a curved yard and a sprit perpenduclar to the yard. This allows a greater control of the sail shape than the traditional Gibbons rig, while retaining the simple shunting method, and is often referred to as the Gibbons/Dierking rig.
The Bruce foil is a foil that provides a lateral resistance with zero heeling moment by placing the foil to the windward side, angled so the direction of the force passes through the center of effort of the sail. Since proas already have an outriger to the windward side, a simple angled foil mounted on the ama becomes a Bruce foil, making the already stable proa even more stable. Bruce foils are often combined with inclined rigs, which results in a total cancellation of heeling forces. Inclinced rigs are also well suited to the proa, as the direction of incline remains constant during shunting.
Another use of foils is to provide lift, turning the boat into a hydrofoil. Hydrofoils require significant speeds to work, but once the hull is lifted out of the water, the drag is significantly reduced. Many speed sailing designs have been based on a proa type configuration equipped with lifting foils.
In a non-traditional variant, first seen among Western yacht racers, the "Atlantic proa" has an ama which is always to the lee side to provide buoyancy for stability, rather than ballast as in a traditional proa. Because the Atlantic ama is at least as long as the main hull, to reduce wave drag, this style can also be thought of as an asymmetric catamaran, that shunts rather than tacking. The first Atlantic proa was the Cheers, designed in 1968 by boat designer Dick Newick for the 1968 OSTAR solo translatlanic race, in which it placed third. Newkirk's designs are primarily trimarans, and the Atlantic proa's buoyant outrigger follows naturally from a conversion of a trimaran from a tacking to a shunting vessel.
Other proa designers blur the lines between Atlantic and Pacific style proas. The Harryproa from Australia uses a long, thin hull to lee, and a short, fat hull, containing the cabin, to windward. This would normally be more like an Atlantic proa, but the rig is on the lee hull, leaving it technically a Pacific design. This and other similar proas place the bulk of the passenger accommodations on the ama, in an attempt to make the vaka as streamlined as possible, and put much of the mass in the lee side to provide a greater righting moment.
Perhaps the most extreme variants of the proa are the ones designed for pure speed. These often completely discard symmetry, and are designed to sail only in one direction relative to the wind; performance in the other direction is either seriously compromised or impossible. These are "one way" proas, such as world record speed holding Yellow Pages Endeavour, or YPE. While the YPE is often called a trimaran, it would be more correct to call it a Pacific proa, because two of the planing/hydrofoil hulls are in line. This design has been considered by others as well, such as the Monomaran designs by "The 40 knot Sailboat" author Bernard Smith, and has been called a 3-point proa by some, a reference to the 3 point hulls used in hydroplanes. A previous record holding design, the Crossbow II, owned by Timothy Colman was a proa/catamaran hybrid. Crossbow II was a "slewing" catamaran, able to slew her hulls to allow clear airflow to her leeward bipod sail. Although the hulls appeared identical, the boat had all crew and controls, cockpit etc. in her windward hull; the leeward hull was stripped bare for minimal weight.