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Fish Keel
A keel for sail boats in the form of a heavy foil suspended from a boat | |
The short version is that this boat can go faster and can go in shallower water. Here comes the long version:
Some modern racing sail boats such as the awesome Volvo Open 70's use canting keels (see link), which helps to reduce heel better then a conventional keel. I have an inexpensive alternative
to the canting keel. Enter the Fish Keel.
A heavy foil similar to a traditional keel is suspended from the boat. The keel hangs deep in the water, from two lines on port and starboard that are connected to winches on deck. By varying the relative length of the lines with the winches, the weight of the keel can be shifted to starboard or to port. In addition, the back of the keel has a vertical fin, similar to the tail fin of a fish, that can be tilted to the left or to the right by control cable to move the fish keel to port or starboard while the boat is moving and provide the lift needed to reduce drift.
I included an illustration to... to illustrate the idea. Please see link. Thank you.
Please note, the Fish Keel is not a fish. It's a keel and a foil. I call it a Fish Keel because it looks somewhat like a fish. For style, it's shaped and painted like a fish in my illustration, but it wouldn't have to look like that. It's made out of lead encapsulated in fiberglass.
The attachment point of the lines on the Fish Keel is forward enough that the keel will not start spinning when the tail fin/keel rudder is angled. The center of gravity of the keel is sufficiently low to leave the keel hanging vertically. The total weight of the keel ranges from nearly a thousand pounds to several thousand pounds, depending on the size of the boat and is sufficient that the boat will not lift the keel out of the water. The horizontal fins/wings on the keel only function to stabilize it a bit and may not even be necessary.
I'm aware that I have not drawn or specified the control mechanism for the tail fin and I'll leave this open to suggestions.
In very shallow water, the keel can even be abandoned with a floating marker and the boat can be beached.
(?) Fish Keel Illustrated
http://www.jacksont.../projects/fishkeel/
[jmvw, Nov 17 2006]
Canting keels
http://en.wikipedia.org/wiki/Canting_keel
[jmvw, Nov 17 2006]
(?) Canting Keel: How It Works
http://www.theage.c.../1135732645000.html
An illustration for those who need it. [jurist, Nov 19 2006]
[link]
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Is this anything to do with a sea anchor? |
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No. A sea anchor is like a small parachute in the water to slow you down in a storm. The Fish Keel is heavy, hangs deep under water and fulfills the two functions of a sailboat keel: |
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1 - it counters the forces on the sails that make a boat heel (lean over). |
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2 - the foil shape produces lift that allows the boat to go forward instead of sideways |
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Function 1 will be performed better then by a traditional keel because of leverage. A tradional keel doesn't produce much torque until the boat is heeling pretty good and the keel is being lifted to the side. This keel has an extra control compared to a fixed keel: it can be pulled to the windward or leeward side (windward is the side of the boat where the wind comes from) and because the fish keel exerts its force further sideways from the center of gravity it has greater leverage and thus the boat can carry more sail and thus go faster then a boat with a traditional keel. |
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The effect is similar to a canting keel, which is a keel on a pivot that can be twisted to either side of the boat, but it should be less expensive then a canting keel and another advantage is that the fish keel can be (temporarily) abandoned and you'll have a boat with very little draft that can go in very shallow water where regular boats can not go. |
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The short version is that this boat can go faster and can go in shallower water. |
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Your illustration does not depict any kind of rigid support to the Fish Keel. Without attachment to a rigid strut or centerboard of some type, what keeps the Fish Keel beneath the boat when it is underway, as opposed to ineffectively trailing behind in the wake?
And how does it provide "lift" with nothing more solid than a pair of lines to rise against? |
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When the boat moves, the keel is not necessarily underneath the boat. Very likely it is located upwind and possibly slightly behind the boat. As for the lift, lift is not necessarily a vertical force. In the case of this and all sailboat keels, the lift is a horizontal force that counters drift. The keel can be compared to an airplane wing that is stuck into the water with the airplane flipped on its side. My illustrations are indeed limited. I don't know the first thing about drawing. I can argue until you're sick of me, though. |
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But don't the lines in the water just create additional drag? [Edit: My experience with racing sails was limited to Y-Flyers, C-Scows and E-Scows on the Great Lakes 35 years ago. When we wanted to rearrange the weight distribution of those little boats to keep them from heeling over under sail, we just clambered over the deckrails onto the exposed centerboard, keeping one hand on the tiller extension and the other wrapped around a line to the mainsail, always aiming to keep our Topsiders dry and appearance of cool control intact while making it look as life-threateningly dangerous as possible to spectators. How the Fish Keel would work without that rigid centerboard or daggerboards or strutted outrigger is kind of unfathomable to me.] |
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They would, but the benefits would outweight the small amount of drag. Thank you for finding the nice image about canting keels. |
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I had a brief chance to sail on an E-Scow this summer. It was a fantastic experience and I will be happy if I can crew on one next year. The Scow is not a keelboat, but if it were, I think the fish keel might be too much to handle on an E-Scow, since there is so much else that needs attention. And it might also be too slow to do a quick tack. |
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A helpful way to understand the fish keel might be to compare it to a kite (like a kitesurfing kite) that would be flown underwater. The lift of the kite would counter drift. |
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I think the concept is sound, but to implement it would require much R&D. |
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the link to your drawing is not working. |
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