I've been experimenting with the daggers lately and I'd like input from past and present Hobie 18 racers.
Because of the shape of the H18 daggers, if they are raised completely into the (large) trunk a gap is created which sucks water up the leading edge of the trunk. It can't be fast to drag two vertical surfaces through the water.
So lately I've been only raising the boards downwind until the leading curve of the dagger starts to separate from the trunk. There is still some gap unless the board is kept low enough so that the full width of the board is at the bottom of the trunk.
So where is the sweet spot? Does boat/wind speed enter in?
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Damon Linkous
1992 Hobie 18
Memphis, TN
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How High To Raise Hobie 18 Daggerboards Downwind
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Posted: Jun 15, 2015 - 07:24 PM
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Posted: Jun 16, 2015 - 11:40 AM
I don't have my boat in front of me right now, but I would estimate between 18"-24". You are correct, if you raise them too high, you will cause drag from the trunk opening. I think you're definitely better off leaving a little extra down than pulling too much up.
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Posted: Jun 17, 2015 - 09:24 PM
Randy Smyth addresses this for the P19 and 18-2 centerboards in Rick White's Catamaran Racing: For the 90's. Downwind he brings the boards up to halfway, at which point they completely fill the well opening. I think the best you can do is figure out where that point is on your daggerboards.
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Posted: Jun 22, 2015 - 12:24 AM
We used to put the boat on the trailer. Fairly easy in the spring when the boards have just been refinished for the season, and slide them in until a Scientific WIld Ass Guess figured the extra drag from the hollow at the front would balance the reduced drag from the extra wetted surface. Then draw a line along the board at deck level. Then downwind the crew just had to raise the boards until the line was visible at deck level.
From my experience I'd say the drag from even a small hollow where the board starts to round off is larger than the skin drag of a lovingly wet sanded board.
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