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Aship's wheel orboat's wheel is a device used aboard aship,boat,submarine, orairship, with which ahelmsmansteers the vessel and controls itscourse. Together with the rest of the steering mechanism, it forms part of thehelm (the termhelm can mean the wheel alone, or the entire mechanism by which the rudder is controlled[1]). It is connected to a mechanical, electricservo, orhydraulic system which alters the horizontal angle of the vessel'srudder relative to itshull. In some modern ships the wheel is replaced with a simple toggle that remotely controls an electro-mechanical or electro-hydraulic drive for the rudder, with a rudder position indicator presenting feedback to the helmsman.
Until the invention of the ship's wheel, the helmsman relied on atiller—a horizontal bar fitted directly to the top of therudder post—or awhipstaff—a vertical stick acting on the arm of the ship's tiller. A ship's wheel was awindlass connecting to the end of the lever that controlled the rudder. However, the end of the lever moved in an arc, while the ropes of the windlass moved in straight lines. For a ship's wheel to be functional, its mechanism had to compensate for this discrepancy, or else the tiller-rope would slacken and tighten throughout the arc, and would be liable to snap. An early solution to this problem was a mechanism in which the tiller-rope was braced against a curved sweep at the head of the tiller. This innovation appears to have been introduced near the start of the 18th century, although the name of the inventor, country of origin, and exact date of introduction have not been identified. The ship's wheel was commonly used from this time, with the French officially adopted the ship's wheel in 1709 and the Venetians in 1719.[2]
A ship's wheel is composed of eight cylindrical woodenspokes (though sometimes as few as six or as many as ten or twelve depending on the wheel's size and how much force is needed to turn it.) shaped likebalusters and all joined at a central woodenhub ornave (sometimes covered with a brassnave plate) which houses theaxle. The square hole at the centre of the hub through which the axle runs is called thedrive square and was often lined with a brass plate (and therefore called abrass boss, though this term was used more often to refer to a brass hub and nave plate) which was frequently etched with the name of the wheel's manufacturer. The outer rim is composed of sections each made up of stacks of threefelloes, thefacing felloe, themiddle felloe, and theafter felloe. Because each group of three felloes at one time made up a quarter of the distance around the rim, the entire outer wooden wheel was sometimes called thequadrant. Each spoke runs through the middle felloe, creating a series of handles beyond the wheel's rim. One of these handles/spokes was frequently provided with extra grooves at its tip which could be felt by a helmsman steering in the dark and used by him to determine the exact position of the rudder—this is theking spoke, and when it pointed straight upward the rudder was believed to be dead straight to the hull. The completed ship's wheel and associated axle and pedestals might even be taller than the person using it. The wood used in construction of this type of wheel was most often eitherteak ormahogany, both of which are very durable tropicalhardwoods capable of surviving the effects of salt water spray and regular use without significant decomposition. Modern design—particularly on smaller vessels—can deviate from the template.
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The steering gear of earlier ships' wheels sometimes consisted of a double wheel where each wheel was connected to the other with a woodenspindle that ran through abarrel ordrum. The spindle was held up by twopedestals that rested on a woodenplatform, often no more than a grate. Atiller rope ortiller chain (sometimes called asteering rope orsteering chain) ran around the barrel in five or six loops and then down through twotiller rope/ chain slots at the top of the platform before connecting to twosheaves just below deck (one on either side of the ship's wheel) and thence out to a pair of pulleys before coming back together at the tiller and connecting to the ship's rudder. Movement of the wheels (which were connected and moved in unison) caused the tiller rope to wind in one of two directions and angled the tiller left or right. In a typical and intuitive arrangement, a forward-facing helmsman turning the wheelcounterclockwise would cause the tiller to angle to starboard and therefore the rudder to swing to port causing the vessel to also turn to port (see animation).[3]: p.152 Having two wheels connected by an axle allowed two people to take the helm in severe weather when one person alone might not have had enough strength to control the ship's movements.
When at the full extent of travel, the wheel and rudder are said to be "hard over", hence the order "hardport/starboard" given byCaptain/Officer of the Watch.
