Ship's wheel

Iconic image of ahelmsmanat a ship's wheel: theGloucester Fisherman's Memorial.

Aship's wheelorboat's wheelis a device used aboard awater vesselorairship,in which ahelmsmansteersthe vessel and control itscourse.Together with the rest of the steering mechanism, it forms part of thehelm(the termhelmcan mean the wheel alone, or the entire mechanism by which the rudder is controlled). It is connected to a mechanical, electricservo,orhydraulic systemwhich alters the horizontal angle of the vessel'srudderrelative 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.

History

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. Near the start of the 18th century, a large number of vessels appeared using the ship's wheel design, but historians are unclear when the approach was first used.

Design

Diagram of the steering gear of an 18th- to 19th-century sailing ship

Helm ofTSGolden Bear

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 likebalustersand all joined at a central woodenhubornave(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 squareand 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 eitherteakormahogany,both of which are very durable tropicalhardwoodscapable 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.

Mechanism

Front and overhead view of a traditional ship's wheel in motion.

The steering gear of earlier ships' wheels sometimes consisted of a double wheel where each wheel was connected to the other with a woodenspindlethat ran through abarrelordrum.The spindle was held up by twopedestalsthat rested on a woodenplatform,often no more than a grate. Atiller ropeortiller chain(sometimes called asteering ropeorsteering chain) ran around the barrel in five or six loops and then down through twotiller rope/ chain slotsat the top of the platform before connecting to twosheavesjust 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).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.

Gallery

• 
  Britannia Yacht Club's Commodore Boardroom features a ship's wheel table
• 
  USSLST-325ship's wheel andengine order telegraph,the latter also referred to in theUS Navyas thelee helm
• 
  U.S. Navy personnel aboardUSSConstitution,by the ship's wheel
• 
  Ship's wheel pictured in the coat of arms ofKitee

See also

• Steering engine
• Steering wheel
• Tiller