As the underside of the hull turns upwards towards the stern the keel can be extended into a significant sized skeg. Depending upon how deep this is it can be quite or even very effective at stopping leeway. Long keel boats generally point well upwind but this does depend upon the design. They work well on displacement boats but not so well on planing boats because there is not enough keel in the water at the bow to prevent the bows being pushed to leewards by the wind. This is where the centreboard or daggerboard has the advantage. Some trimarans use a skeg under their amas (floats) to prevent leeway. To be effective the boat must be heeled over a little by the wind, as trimarans usually are when reaching or especially beating upwind. However, the trimaran would sail faster if kept level provided that the leeway could be prevented by some other means. Crew weight can be used to bring the trimaran level but a skeg mounted on the ama would no longer prevent leeway. This is where the centreboard scores.
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