Why Boards instead of Keels

I am a big advocate of boards instead of keels on multihulls. I understand the preponderance of production multihulls have keels. And boards can mess up the interior. The big deal, I think, is the greater lift that a board generates. When I got new computer a while ago, I had not gotten around to downloading Dave Vacanti’s Loft 97 foil creating program again. He has a free demo of it. I urge you to compare keels to boards on your own.
Keep in mind that nothing else will push you windward except lift.
See http://vacantisw.com/ Go to the free downloads.
For example lets compare 16 square foot foils. Same foil family, NACA 00. For simplicity, no sweep.

Assume a board with 2′ chord and 8′ draft.¬† At 5 knots the board generates 800 lbs of lift. At 20 knots, 12,000 lbs of lift.
Next, a ¬†keel of 2′ draft and 8′ chord creates 120 lbs of lift at 5 knots, and 2,400 lbs at 20 knots.

Now look at a common 1′ deep keel. At 5 knots, 35 lbs of lift. At 20 knots, a mere 550 lbs of lift. People. Again, nothing else will push you to windward except lift.

And as I tell my catamaran customers with keels, take a cell phone with a marine towing service on the speed-dial. If they run aground, a mono can kedge off of the mast and get free. A trimaran can chase everybody onto the ama and get free. If the tide is going out, a cat with keels will spend the next several hours there. Period.

Finally, if you stuff it up on a rock, with a keel you must haulout to fix. With a board you can keep sailing as you repair the board.


4 thoughts on “Why Boards instead of Keels”

  1. It’s so simple, but you can debate this point for days on end in the general public forums. Boards get you to windward, making a faster multihull. Period.

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