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What are the different Boat Keel Types. Bulb Keel, Wing/bulb keels, Lifting keels, Bilge keels

By Stuart Wilson

Bulb Keel

This is much like a fin keel in shape but has a single bulb attached to the very bottom of a keel. This allows ballast to be added to the keel at its very lowest point to improve righting moment without adding excessive weight or increasing the keel depth.
The yacht with this type of keel is responsive and highly manoeuvrable but susceptible to heavy tilting during relatively strong incoming winds.

Wing/bulb keels

Has the shape of a fin but as the name suggests, they take the shape of a wing at the very bottom of the keel and also can have a fat bulb centred at the middle-bottom of the wing. These types of sailboat keels are more often found are longer and heavier boats or high performance sailboats

Lifting keels

A lifting keel is a type of keel that can be retracted, or lowered usually from the cabin.

The main advantage of lifting keel sailboats is the possibility of exploring shallow waters that would be inaccessible to deep draft sailboats. Other advantages of a lifting keel is that the boat can dry out on a beach or harbour and remain horizontal plus launching and recovery from a slipway is far easier as is transporting the boat on a trailer

Lifting keels have a number of different systems. One which most people will be familiar with is a dagger board in a sailing dingy which when retracted sits in a housing in the centre of the dingy. Larger sailing boats may have the keel box (that the keel retracts into) inside the boat usually in the saloon area where it forms an integral support for the dining table. Another arrangement is for the keel to retract into a stub keel which is situated in the centre of the hull below water. This avoids the keel taking up space internally and presents the possibility of dividing the ballast between the stub keel and the retractable keel.

Some sailors dislike a lifting keel arrangement because mud, debris or stones can become trapped in the keel; box resulting in damage, more maintenance and the danger that the keel cannot be lowered when it is really needed

Bilge keels

Bilge keels, are also referred to as twin keels, and because of their relative shallow draught are popular for use in rivers, estuaries and shallow coastal waters. The other advantage is that if the mooring dries out at low tide the boat will settle on the shallow keels located on each side of the hull pointing down and. splayed out at an angle The benefit of this arrangement means that the boat remains upright and stable when aground without the need of propping. This would not be the case with a keel situated in the centre of the hull

The early generation of bilge keels provided an inferior sailing performance compared to modern fin keels because of their shallow draught, angle and position of the keels on the hull. This produced a weaker righting movement and weaker resistance to leeway. The shapes of bilge keels have evolved and because of changes to the angle of the keels on the hull of around 20 degrees from the vertical, and an increase in length, the draught of one keel increases when the boat heels over and results in an increase in performance. Overall the sailing experience of a bilge l keeled boat would generally be considered inferior to a fin keeled boat because its larger wetted surface produces more drag and a resulting decrease in speed especially in light winds.

This article was last update on 24-10-2019 at 10:28