Sailboat Keel Shapes

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Full Keel

full keel sailboat
Photo © Tom Lochhaas.

A sailboat’s keel keeps the boat from being blown sideways, converting lateral forces of the wind to forward thrust. Weighted keels also provide ballast low in the water to resist the heeling force of wind sideways on the sails. Different sailboats have different kinds of keels.

The length of the keel (in a fore-aft direction) varies considerably among different types of sailboats. On one extreme is the traditional full keel, running much of the waterline length of the hull. At the other extreme is the contemporary narrow fin keel, swing keel, or centerboard.

Advantages of Full Keel Sailboats

Disadvantages of Full Keel Sailboats

Full-keel boats are slower to turn when the rudder is moved and may be difficult to tack (turn across the eye of the wind) in light wind. Because the larger surface area below the waterline causes more drag, full-keel boats are also usually somewhat slower than boats of the same size with a fin keel.

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Fin Keel

Sailboat Fin Keel
Photo © Tom Lochhaas.

A fin keel is much shorter (fore-and-aft) than a full keel. A fin keel is often deeper, in order to move the ballast weight as low as possible in the water.

Advantages of Fin Keel Sailboats

Disadvantages of Fin Keel Sailboats

Because the shorter keel provides less resistance to forces that act to throw a sailboat off course, such as wind gusts and waves, a fin-keel sailboat does not track as well as a full-keel boat and requires more attention to the helm. Its motion may not be as sea-kindly.

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Fin Racing Keel

Sailboat Fin Racing Keel
Photo © Tom Lochhaas.

In cruiser-racers, the fin keel is generally deeper and shorter in fore-aft length (as shown here) than the more common fin keel found on most cruising sailboats.

Serious racing boats such as the Open 50 or Open 60 class boats replace the fixed fin keel with a very narrow, very deep keel with a ballast bulb at the bottom. The canting keel can be moved sideways to provide more resistance to heeling. Because the keel is so narrow, daggerboards are often used to provide additional resistance to the lateral force of the wind.

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Bulb and Wing Keels

Sailboat Wing Keel
Photo © Tom Lochhaas.

In the last two decades fin keels with a bulb and/or “wings” at the bottom have appeared more frequently on production sailboats. The bulb provides more ballast weight without the keel having to go deeper—thus these boats may be sailed in shallower waters. The wings at the trailing edge of the keel provide additional hydrodynamic stability.

Otherwise, bulb and wing keels have similar advantages and disadvantages as a fin keel when compared to a full keel.

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Close-Up of Keel Wing

Sailboat Wing Keel Closeup
Photo © Tom Lochhaas.

Here’s a close-up view of a keel wing protruding sideways from the bulb.

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Swing Keels and Centerboards

Both full-keel and fin-keel sail boats generally have fixed keels. On many smaller boats, however, the keel can be swung up into the hull from a pivot point at the top. This allow the boat to be positioned lower on a trailer or to maneuver in shallow water.

A swing keel is a weighted, narrow, fin-type keel that provides both ballast and lateral stability. A centerboard is similar but often is not weighted and thus provides only lateral stability.

Some larger cruising boats have a centerboard that can be lowered from within a fixed long keel, giving more lateral resistance when lowered for sailing close to the wind but a shallower draft and less drag when raised for sailing downwind or in shallower water.

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Rudder and Keel Combination

Sailboat Fin Keel Spade Rudder
Photo © Tom Lochhaas.

The boat’s rudder configuration is often related to keel shape. A boat with a fin keel often has a free-standing spade rudder such as shown here, while a full-keel boat generally has a rudder attached to the aft end of the keel. See also this article on rudders.