Nautical Terms - page 2

1.2 Types of hull, keel and Rudder

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Keel - What does it do?

The keel is basically a flat blade sticking down into the water from a sailboat’s bottom. It has two functions: it prevents the boat from being blown sideways by the wind, and it holds the ballast that keeps the boat right-side up.

Draught

Vessel draft (draft in the American spelling, draught in the British) is one of the principal dimensions of any waterborne vessel and is defined in technical terms as the distance between the ship's keel and the waterline of the vessel.

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Traditional long keel

Yacht with long keels are generalliy heavier and narrower than the modern short-keeled boat and are favoured by blue water sailors for their stability and seakindliness in a blow. The narrow beam reduces living space down below and the long keel means that the turning circle is greater than for shorter-keeled boats. It will be difficult to take her astern in a straight line under power, so berthing stern first is not a good option. 

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Mid-lenght keel & rudder with skeg

Moderation in all things is often a good philosophy, those who want a good working compromise will choose a hull with a medium-lengh keel and a rudder that is supported over its full lenght with a skeg. This type of yacht will handle tolerably well under power and has a large enough keel area to limit the amount of leeway she makes. Many production cruising boats are of this design and have sufficient beam to satisfy the demand for separate cabins and spacious saloons.  

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Twin bilge keels

A boat with bilge keels would be the better bet as this type will sit down on both keels if the seabed is even and not tip its owners out of bed in the middle of the night as it takes to the ground. Many cruising folk like to keep berthing costs down and to enjoy quiet corners away from marinas and draught of a bilge keeler when upright. The downside is that performance upwind can be affected by the water flow around the uppermost keel. 

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Lifting or swing keel

A lifting keel may be the perfect answer for a berth with restricted water and the one in the photo has a very shallow draught. There usually has to be some compromise for convenience space will be taken up in the cabin by the keel housing, which is often heavily disguised as part of the saloon table. Early models of swing and lifting keels made of a lot of noise down below when the boat was sailing downwind.

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Catamaran

Twin-hulled yachts are favoured by those chartering in exotic places because their boat remains flat while sailing and accommodation is spacious. Sailing performance when running downwind is good, but their windward performance is generally poor and the bow turns through the wind slowly. Berthing in a marina can be difficult as many visitors berths are not wide enough for the two hulls, but when lying to a mooring with plenty of swinging room, there should be no problem. Marinas often charge double to berth a cat. 

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Wing keels

Short fin keels are sometimes given "wings" to reduce the draught without decreasing the weight of the ballast. Sailing performance is not affected, but if the boat accidentally runs aground, any attempt to re-float her by heeling just digs one of the wings even deeper into the mud. 

Rudder

Rudder, part of the steering apparatus of a boat or ship that is fastened outside the hull, usually at the stern. The most common form consists of a nearly flat, smooth surface of wood or metal hinged at its forward edge to the sternpost.

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