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Using both side thrusters and main fin

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Created by Francone 5 months ago, 7 Jul 2018
Francone
WA, 208 posts
7 Jul 2018 6:15PM
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Does it increase lift to use both side thrusters and main fin ( weed fin) on my board ( Bic Windsup) or does it create problems ( directional stability ) especially with the main centerboard full down when tacking upwind? What about downwind?

Thanks

Francone

forceten
458 posts
7 Jul 2018 10:37PM
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Select to expand quote
Francone said..
Does it increase lift to use both side thrusters and main fin ( weed fin) on my board ( Bic Windsup) or does it create problems ( directional stability ) especially with the main centerboard full down when tacking upwind? What about downwind?

Thanks

Francone


Yes. Or stability probs associated with a centerboard, probably not unless the side fins are too large. Most sailors dont use a centerboard with a tri fin setup so little scientific data is available on this. When I made a BIC Presto for my 9YO to learn on, a tri fin conversion with a non retractable fin placed as a centerboard, tacking , was enhanced , Directional stability was improved overall, without detracting from a multi fin setup. Use of asymmetrical sides VS dual foils helped in feel.

Francone
WA, 208 posts
8 Jul 2018 6:11AM
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Select to expand quote
forceten said..

Francone said..
Does it increase lift to use both side thrusters and main fin ( weed fin) on my board ( Bic Windsup) or does it create problems ( directional stability ) especially with the main centerboard full down when tacking upwind? What about downwind?

Thanks

Francone



Yes. Or stability probs associated with a centerboard, probably not unless the side fins are too large. Most sailors dont use a centerboard with a tri fin setup so little scientific data is available on this. When I made a BIC Presto for my 9YO to learn on, a tri fin conversion with a non retractable fin placed as a centerboard, tacking , was enhanced , Directional stability was improved overall, without detracting from a multi fin setup. Use of asymmetrical sides VS dual foils helped in feel.


Thanks

I am asking because I just put on a new large weed fin ( 9" wide at the top,tapering of course, 17 " long, 14 " deep) while keeping the thrusters .

On one hand, I seem to find the board plowing more forcefully and faster through the water( more lift?), but I also had problem in controlling it later on when tacking upwind with the centerboard full down. Maybe there was some kind of destabilization due to the interaction between the centerboard, the large fin and the thrusters. The board seemed to turn in the opposite direction of the one intended when tacking and I was bumped off a couple of times. Kind of swirling. Never happened before. It could also be because the winds started shifting erratically from WSW to due South back to WSW for a while and this caused problems in the middle of the tacking maneuver when you change side, because now the " good" side . becomes the bad side once the winds have suddenly shifted..
I'll remove the thrusters next time and see how it goes.

Francone

Mark _australia
WA, 18520 posts
8 Jul 2018 1:52PM
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What sort of speed

In non planing conditions I can't see the side fins would make any significant difference

As to turning the wrong way, big boards in light winds with the centreboard down do require pressure on the opposite rail to turn (totally opposite to a carve gybe)

forceten
458 posts
8 Jul 2018 10:09PM
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Have your site checked for ALIENs

forceten
458 posts
8 Jul 2018 10:09PM
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Dupe deleted

forceten
458 posts
8 Jul 2018 10:16PM
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You normally , size down the center fin when using thrusters . The formula that Maui Ultra Fin use is : The appropriate center fin area when used as a single, times 1.5 for the totalfin area of a thruster/tri fin setup. This is rather loosely based, and probably doesnt apply at all for a board using a dagger board. If the side bites(thrusters) are very small in a board this large it may not matter at all.

Again you find issues no one else experiences. Check for little green men, disturbing the water



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"Using both side thrusters and main fin" started by Francone