A thwart is a part of an undecked boat that provides seats for the crew and structural rigidity for the hull. A thwart goes from one side of the hull to the other. There may be just one thwart in a small boat, or many in a larger boat, especially if several oarsmen need to be accommodated.
A thwart is a part of a boat that usually has two functions: as a seat, and as a structural member that provides some rigidity to the hull. A thwart goes from one side of the hull to the other in an open (undecked) boat, and therefore resists forces pushing in or pulling out the sides of the hull. More obviously it provides a seat for an occupant of a boat. In many sailing boats, a thwart may help support the mast. This can be done either by inserting the mast through a hole in the thwart (with the end resting in a mast step on the keel), or the mast may be clamped to one side of a thwart –this makes it easier to step and unstep the mast whilst afloat. [1] : 1148 [2] : 149
In a boat propelled by oars, the thwart has to be positioned with the right geometry for the oar to be worked efficiently and comfortably. Firstly, with a rearward facing oarsman, [lower-alpha 1] the thwart has to be nearer the front of the boat than the pivot point for the oar (which acts as a fulcrum). The usual distance between the after edge of the thwart and the oar's pivot is 10–12 inches (250–300 mm). The next consideration is height. The oarsman has to be positioned so that during the recovery part of the stroke, the oar is above the surface of the water, allowing for the height of waves which the boat might encounter. Since the oarsman is seated, the inner end of the oar cannot go any lower than
t the top of their thighs –and some clearance is needed for comfort. This usually translates into the top of the thwart needing to be 10–12 inches (250–300 mm) below the point on the gunwale where the oar is pivoted. With these two parameters fixed, the oarsman then needs the support for their feet to be in the right place. As the power of the stroke is delivered, the force applied by the oarsman is reversed in direction by the fulcrum of the oar pivot. The oarsman's feet have to be high enough to take the horizontal component of that force. Especially in larger boats, a footrest or "stretcher" is provided for this. It is usually adjustable for the height of the oarsman. [2] : 137 Another consideration for the position of a thwart is the fore and aft distribution of weight in a boat. In a utility sailing dinghy that is being rowed there may be two alternative rowing positions. If a crewmember is steering, the rower sits on a forward thwart, thereby distributing the weight around the boat evenly –but if the rower is alone, better balance may be achieved using a thwart that is further aft. [3] : 97
Thwarts in a boat worked under oars may be described as either "single banked" or "double banked". With a single banked arrangement, there is one oarsman seated on each thwart, each of whom is working only one oar. The oars alternate on each side along the length of the boat. This allows a boat to be reasonably narrow and yet still have ample length of oar inboard of the gunwale (the oarsman can sit off the centre line of the boat to maximise this length). A double banked boat has two oarsmen seated on each thwart, each of whom operates their own oar on their own side of the boat. This is generally found in larger boats. A third arrangement is where two oars, one each side of the boat, are worked by one person. (Technically, in salt water, this is the only use of an oar that is termed "rowing". In inland waters, it is termed "sculling" and "rowing" means working a single oar. This strict and contradictory terminology is not always adhered to.) [2] : 137
Most commonly, a thwart is a single timber plank. It usually needs to be firmly attached to the hull. In a traditional wooden construction it usually sits upon, and is fastened to, a longitudinal stringer which is sometimes called a shelf. The joint between hull and thwart is often reinforced with pairs of knees. [lower-alpha 2] Traditionally, knees are grown to the required shape, so that the grain follows the shape. In modern construction, glued laminated timber knees may be used. In larger boats, the centre of the thwart is supported with a pillar that goes down to the keel. In a sailing dinghy, all or some of the thwarts may be built in with the structure of the centre-board case. [4] : 210–217
In lightly-built whaleboats, the thwarts deliberately had a slight upwards bend in the middle. This meant that if the hull received a blow on the side, it could momentarilty flex slightly as the thwarts bent slightly more –without this, the force of the blow would punch a thwart through the side of the hull, making a large hole. [5]
In a canoe, a thwart is simply a strut placed crosswise (left/right) in a ship or boat, serving only as a structural member or to help with carrying. Some inflatable boats have a solid thwart which can be folded and removed so the boat can be deflated and rolled up for transport or storage. [6] [7]
Rowing, often called crew in the United States, is the sport of racing boats using oars. It differs from paddling sports in that rowing oars are attached to the boat using rowlocks, while paddles are not connected to the boat. Rowing is divided into two disciplines: sculling and sweep rowing. In sculling, each rower holds two oars, one in each hand, while in sweep rowing each rower holds one oar with both hands. There are several boat classes in which athletes may compete, ranging from single sculls, occupied by one person, to shells with eight rowers and a coxswain, called eights. There are a wide variety of course types and formats of racing, but most elite and championship level racing is conducted on calm water courses 2 kilometres (1.2 mi) long with several lanes marked using buoys.
A trireme was an ancient vessel and a type of galley that was used by the ancient maritime civilizations of the Mediterranean Sea, especially the Phoenicians, ancient Greeks and Romans.
A dinghy is a type of small boat, often carried or towed by a larger vessel for use as a tender. Utility dinghies are usually rowboats or have an outboard motor. Some are rigged for sailing but they differ from sailing dinghies, which are designed first and foremost for sailing. A dinghy's main use is for transfers from larger boats, especially when the larger boat cannot dock at a suitably-sized port or marina.
A yawl is a type of boat. The term has several meanings. It can apply to the rig, to the hull type or to the use which the vessel is put.
An oar is an implement used for water-borne propulsion. Oars have a flat blade at one end. Rowers grasp the oar at the other end.
Boat building is the design and construction of boats — and their on-board systems. This includes at minimum the construction of a hull, with any necessary propulsion, mechanical, navigation, safety and other service systems as the craft requires.
An outrigger is a projecting structure on a boat, with specific meaning depending on types of vessel. Outriggers may also refer to legs on a wheeled vehicle that are folded out when it needs stabilization, for example on a crane that lifts heavy loads.
A cutter is a name for various types of watercraft. It can apply to the rig of a sailing vessel, to a governmental enforcement agency vessel, to a type of ship's boat which can be used under sail or oars, or, historically, to a type of fast-sailing vessel introduced in the 18th century, some of which were used as small warships.
A lugger is a sailing vessel defined by its rig, using the lug sail on all of its one or more masts. Luggers were widely used as working craft, particularly off the coasts of France, England, Ireland and Scotland. Luggers varied extensively in size and design. Many were undecked, open boats, some of which operated from beach landings. Others were fully decked craft. Some larger examples might carry lug topsails.
A gig is a type of boat. It was optimised for speed under oar, but usually also fitted with a sailing rig for appropriate conditions. The type was in use by Deal boatmen in the 18th century. It first occurred as a naval ship's boat after Deal boatbuilders recommended a different design to boats ordered from them by the Royal Navy to equip the cutters purchased in the 1760s to combat smuggling. The captains of larger warships soon sought permission to substitute a gig for one of the heavier boats which were then used; some even had a gig built at their own expense. The gig therefore became part of the usual complement of ship's boats used in warships.
Clinker-built is a method of boat building in which the edges of hull planks overlap each other. Where necessary in larger craft, shorter planks can be joined end to end, creating a longer strake or hull plank.
Rowing is the act of propelling a human-powered watercraft using the sweeping motions of oars to displace water and generate reactional propulsion. Rowing is functionally similar to paddling, but rowing requires oars to be mechanically attached to the boat, and the rower drives the oar like a lever, exerting force in the same direction as the boat's travel; while paddles are completely hand-held and have no attachment to the boat, and are driven like a cantilever, exerting force opposite to the intended direction of the boat.
In watercraft, a racing shell is an extremely narrow, and often comparatively long, rowing boat specifically designed for racing or exercise. It is equipped with long oars, outriggers to hold the oarlocks away from the boat, and sliding seats. The boat's long length and semicircular cross-section reduce drag to a minimum. This makes the boat both fast and unstable. It must be balanced by the rowers to avoid tipping. Being able to balance – or "set" – the boat while putting maximum effort into the oars is therefore an essential skill of sport rowing.
In competitive rowing, the following specialized terms are important in the corresponding aspects of the sport:
Henry (Harry) Clasper was a professional rower and boat builder from Tyneside in England. He was an innovative boat designer who pioneered the development of the racing shell and the use of outriggers. He is said to have invented spoon-shaped oars.
In rowing, oars are used to propel the boat. Oars differ from paddles in that they use a fixed or sliding fulcrum, an oarlock or rowlock attached to the side of the boat, to transfer power from the handle to the blade, rather than using the athlete's shoulders or hands as the pivot-point as in canoeing and kayaking.
Boats used in the sport of rowing may be adjusted in many different ways according to the needs of the crew, the type of racing, and anticipated rowing conditions. The primary objective of rigging a boat is to accommodate the different physiques and styles of rowing of the crew in such a way that the oars move in similar arcs through the water, thus improving the crew's efficiency and cohesiveness.
Sweep rowing is one of two disciplines of the sport of rowing. In sweep rowing each rower has one oar, usually held with both hands. As each rower has only one oar, the rowers have to be paired so that there are equal numbers of oars on each side of the boat. In the United Kingdom, rowing generally refers to sweep rowing only. The term pulling was also used historically. In the other rowing discipline, sculling, each rower holds two oars, one in each hand.
This glossary of nautical terms is an alphabetical listing of terms and expressions connected with ships, shipping, seamanship and navigation on water. Some remain current, while many date from the 17th to 19th centuries. The word nautical derives from the Latin nauticus, from Greek nautikos, from nautēs: "sailor", from naus: "ship".
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