AskDefine | Define proa

User Contributed Dictionary

English

Noun

  1. A sailing vessel found in the waters of Micronesia and Indonesia; it has a single, large outrigger and a triangular sail

Spanish

Noun

  1. bow (front of a boat or ship)

Extensive Definition

A proa 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 the south Pacific islands, 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.

Etymology

The word proa comes from perahu, the word for "boat" in Malay, which is similar to the Micronesian language group. Found in many configurations and forms, the proa was likely developed as a sailing vessel in Micronesia (Pacific Ocean), and forms of it may be found as far as Madagascar and Sri Lanka as far back as the 1st century, and they are known by many names. The use of the term proa in English to refer to the Micronesian craft dates back to at least 1742 (see below).
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.

Proa characteristics

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 aggressively 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 will use leeboards for lateral resistance.
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.

Size and sail plan

The Micronesian proa is found in a variety of sizes, from the small, canoe-like kor-kor (about 15 feet in length) to the medium sized tipnol (20 to 30 feet), to the tremendous walap, which can be up to 100 feet (30 m) long. There is also a model proa, called a riwuit, that is often raced by children. Proas could be paddled or sailed. The traditional sail used on the proa was the crab-claw sail. The crab-claw sail generates far more lift than the more common triangular sloop sails used on small boats, particularly when reaching. The sloop sail only begins to show an advantage with small angles of attack, such as encountered when beating. This is the result of the higher aspect ratio of the sloop sail.
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.

Sailing the proa

When sailing in a strong wind, the crew of the proa act as ballast, providing a force to counteract the torque of the wind acting on the sail. The weight of the crew can provide considerable torque as they move out along the akas towards the ama. A skilled crew will balance the proa so that the ama leaves the water and skims over its surface; this is called "flying the ama", and gives the proa its nickname, the "flying proa". By flying the ama, the wetted surface, and therefore the drag of the proa is significantly reduced. When combined with the long, narrow shape of the vaka, and the large amount of torque the crew can apply on the akas, this gives the proa its large potential speed.

Historical descriptions of the proa

The Proa darted like a shooting star
Lord Byron, The Island, 1823
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 15191522 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.

Construction

It is fairly certain that the proa evolved from the dugout canoe, one of the oldest watercraft and found in primitive cultures across the world. The design of the proa hints at its evolution from a canoe into the world's fastest sailboat, a title it likely held for many centuries.

Vaka (main hull)

The traditional Micronesian proa hull consists of a single long keel made of a single large log, and constructed much like a dugout canoe. This is then extended upwards with sewn planks, to provide additional depth to the hull. The windward side of the hull is curved, similar to a typical canoe, while the lee side is straight and flat to minimize leeway while sailing.

Roosevelt's Mary & Lamb

Robert Barnwell Roosevelt, uncle of American president Theodore Roosevelt, also built a proa at about the same time. He used it sailing somewhere out of Long Island. It was significantly different but equally creative, and at 50 feet, much longer. As far as can be determined by his 1898 article in The Rudder, the main hull of Roosevelt's proa was an open 4-foot-wide scow hull; the ama was a smaller, fully decked scow which looks like it could rock on a single aka. The mast was a bipod arrangement with both masts stepped to windward, with a boomed, balanced lugsail suspended from the apex. A balanced rudder at each end managed itself by pivoting 180 degrees when its end was the "bow", and leeboards were used.
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.

Munroe's 1900 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:
  • Length overall 30 ft.
  • Beam (of main hull) 2 ft. 6 in.
  • Draft of hull about 5 in.
  • Draft with boards down 2 ft. 5 in.
  • Sail area 240 sq. ft.
From the drawings, the distance from the center of the main hull to the center of the aka is about 12 feet.

Other Western Interpretations

Western designers often feel the need to tinker with the proa. They are attracted by the minimalist nature and amazing speeds that proas are capable of (they may still be the fastest sailboats per dollar spent for the home builder) but they often want the proa to do more; adding cabins, different sailing rigs, and bidirectional rudders are common changes made.
For example, unconventional boat and yacht designer Phil Bolger has drawn at least three proa designs; the smallest one (20 feet) has been built by several people while the larger two, including his Proa 60, have not been built. For additional examples, see here.

Lee pods

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.

Sail rigs

One of the issues Western designers have with the proa is the need to manipulate the sail when shunting. Even Munroe's early sails discarded the curved yards of the traditional crabclaw for the more familiar straight yards of the lateen and lug sails. Munroe's designs likely lacked the tilting mast because he was unaware of it, but many designers since have use a fixed mast, and provided some other way of adjusting the center of effort--which should lead the center of lateral resistance, which in a proa is usually right in the center. The Jzero, for example, used a sloop rig and ran up a jib on whichever end was the current "bow". Other designs use two masts, or a rotating jib/main combination on a large boom.
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.

Foils

While a proa is fairly efficient at minimizing the amount of wave drag and maximizing stability, there is at least one way to go even further. The use of underwater foils to provide lift or downforce has been a popular idea recently in cutting-edge yacht building, and the proa is not immune to this influence.
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.

Variations on the theme

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.

References

  • Canoes of Oceania
  • The Commodore's Story

External links

Sources of information on proas

Individual proa designs

proa in German: Proa
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