Maxi Yacht: How do the keel and the hull align when heeled over?
Modern racing Maxi Yachts are shaped like a wedge of cheese. The keel is aligned axially with the centerline of the boat. When the boat heels over in the wind, the outer edge of the hull is the only part of the boat in contact with the water. In effect, the outer edge of the hull becomes the new hull in water (HIW).
The keel is aligned with the center of the hull, not the HIW. The keel and the HIW form a vertex somewhere ahead of the bow. It seems like this arrangement pushes the HIW somewhat laterally through the water, creating extra drag. In fact, I've observed water spraying up from the waterline near the rear of a boat.
So the question is, can a keel in a Maxi Yacht rotate around its vertical axis (yaw) to re-align with the HIW?
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No the keel doesn't move. You can find the class rules for the Maxi 72 class here. The relevant rule is D.2.4 which specifies
One fixed centreline keel, solid in profile. No part shall be adjustable when racing and there shall be no movement beyond the normal elasticity of the materials used. No wings or winglets.
I short they have a fixed keel.
I suspect what you are seeing is probably just due to the shape of the hull. I couldn't see anything that unusual in the video you linked.
One other possible cause could be the boat planing which will mean the boat mounts its own bow wave, causing it to appear further back.
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I came across this reference on a Seahorse Magazine article:
Negative sideforce is undesirable because it pushes the yacht to leeward thereby increasing leeway angles. Negative keel fin sideforce also comes with an induced drag penalty.
It also discusses inclining the keel pin approximately 5 degrees to reduce these problems. About half of the article focuses on keel designs. The remainder discusses the bulb, canting keel system, daggerboards, and rudder.
So, it seems like the answer to the question is that some designs have rules that allow designers to incline the keel pin and cant the keel, effectively allowing the keel to yaw.
This post was sourced from https://outdoors.stackexchange.com/a/10584. It is licensed under CC BY-SA 3.0.
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