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Go Back   SailNet Community > On Board > Boat Review and Purchase Forum > Sailboat Design and Construction > parallel sails?
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Topic Review (Newest First)
05-28-2010 10:20 PM
donlofland In my old Hobie Cat days, when the wind was in the ?15 knot range, we'd reach with the sails trimmed tight, and then head downwind gradually with as little loss of boat speed as possible, and still not sheet out-the boat speed kept the apparent wind ahead of us. (And I've got to look up pedant-something to do with shoes? :-)
02-16-2010 01:55 PM
bljones The concept sort of worked for Pete Goss and Team Phillips back in 2000. Wickedly fast, but the hulls weren't up to the task, and the masts pivoted on a ball and socket arrangement which was a little problematic.

YouTube - Team Philips... The last ride.

02-16-2010 10:28 AM
sck5 Have you seen one of those hobie trifoils? they go like a bat out of hell. didnt look like either of the sails was having a problem as far as I could see. looked like fun
02-16-2010 10:22 AM
lanekthomas
Blanketing

There is a point of sail, where the wind is abeam and the leward sail is blanketed by the windward. The solution is to ease the windward sail untill it spills enough wind to fill the leward sail. It takes practice but there is really no point of sail that you can not benifit from the parallel rig, it just takes practice.
Lane in Austin TX
01-15-2010 11:48 PM
mitiempo That's right. They start broad reaching and as they pick up speed the apparent wind moves forward of the beam. The tri-foilers move through this stage quickly. The faster they go the more close hauled they are. They tack downwind and even though they cover a greater distance their vmg is better. The tri-foilers in the video never slow down enough for the apparent wind to come aft even when changing direction as they lose very little speed.
01-15-2010 09:57 PM
klem
Quote:
Originally Posted by AdamLein View Post
I'm think it's impossible to sail dead downwind faster than the wind, which means that going DDW in a trifoiler you're not close hauled, which means that your argument - that there should be some angle at which the apparent wind is abeam - still holds.
This is essentially correct. It also describes the interesting shape of the sail polar diagram of these really fast boats.

When sailing dead downwind, you are using the drag of the sails in the air and no lift is being generated (I am ignoring unstayed masts where the sails can be let out further than perpendicular). Therefore, even with infinite drag (roughly proportional to sail area), you still can't outrun the wind. On other points of sail, you use lift rather than drag which allows you to sail faster than the true wind speed. In addition, since you are not pointing in the same direction as the wind, the apparent wind moves forward which explains why the boats always seem to be close hauled. Since these boats are so fast broad reaching, they will tack downwind because it is much faster than running. To see why this is the case given the polar diagram, take a ruler and hold it perpendicular to the true wind direction and slide it in towards the center until you hit the line. On these fast boats, you will hit two points first for going with the wind which correspond to broad reaching on each tack.
01-15-2010 09:32 PM
AdamLein tager: I looked up DDWFTTW and it looks like they're not sailing. i.e. they are propelled neither by an air drag force (downwind sailing) nor by lift forces (upwind sailing). Instead they have an air turbine powering either wheels (for land vehicles) or a propeller.

I'm think it's impossible to sail dead downwind faster than the wind, which means that going DDW in a trifoiler you're not close hauled, which means that your argument - that there should be some angle at which the apparent wind is abeam - still holds.
01-15-2010 07:23 PM
mitiempo If the amas are removeable it should be possible. That would leave you with a kayak and two smaller hulls. And a mast.
01-15-2010 07:16 PM
nickmerc You will probably not be able to cartop a beach cat. I used to tow my Hobie 16 with a VW Passat. The boat was wider than my car. They are also unwiedly to move around solo when not in the water.
________
Volcano Vaporizer
01-15-2010 06:55 PM
mitiempo I see. You don't want to paddle at all.
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