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Old 15th February 2009, 09:58 PM   #1
freeskiing
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Default 2 additional side fins for EVO

do you think bringing 2 additional side-fins on an EVO 70 (i.e. making it a kind of a thruster) would improve the upwind and turning abilities of my board while preserving the stability all the other good features of an EVO?
if yes, how/where would you position the fins (size?).
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Old 16th February 2009, 01:48 AM   #2
Ola_H
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I did that on the 2007 EVO 75 and used it with three fins of about equal size (ie not with a big central and two small side fins). My conclusion is that it really didn't improve the board. Upwind got a tiny big better, but it actually got less loose in the turns and felt a bit slower.

I think that with a tri fin setup, it is absolutely vital to get the fin positioning and angle just right and it takes experimentation to get there. If you still want to do it, a starting point could maybe be 1.5-2 degrees toe in of the side fins, shortest distance from rail to box about 1.5-2cm and then the rear edge of the fins contact point with the board 32cms from the tail.

Pretty much all people experienced with tri fin windsurf designs also seem to recommend symmetrical fins. As for boxes, with really small fins you might get away with fcs, but I think Future boxes would be a beter choice. For a full tri fin setup the mini tuttle design that some kite boards uses (and also Withcraft) should be the best option.

Last edited by Ola_H; 16th February 2009 at 03:44 AM.
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Old 16th February 2009, 02:38 AM   #3
steveC
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freeskiing,

You might want to check out the following website. Probox appears to have developed an interesting finbox design, to include a broad array of fins. The thing that is very nice about their finbox design is that there are a number of canting options available.

http://www.proboxfinsystems.com/pages/products.html
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Old 16th February 2009, 07:15 AM   #4
Mike T
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FreeSkiing
Hi! Freeskiing, You might want to take a look at some of the info from Wardog @ http://www.surfingsports.com/ he has alot of experience with the Trifin setup. He was working with Mark Bassett custom boards out of Corpus Christi,Texas in the 1990's to 2001 and their are some theads on some of the other windsurfing forums on how they perform compared to single fin. Mark stopped building board around summer 2001. From what I've read is that in high wind they slow the board down a little and that gave you a bit more control. I had a West Wind winged pintail thruster back in Corpus Christi 1982 and it was alot of fun to ride but alot of things have changed since then so I would'nt want to compare that board to a new design. Drop Wardog an e-mail and I'm sure he'll give you some insite. I think at one time he had at least 10 of Marks boards. SteveC those are some cool fin boxes! Good luck and warm winds. Mike
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Old 19th February 2009, 12:36 PM   #5
carvesalot
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http://www.kainoalani.com/design/toecalc.html

the numbers that Ola quoted are similar to what I have found ,also the rest of his advise as well.
I'm just starting the tri fin project to a freestyle board.
The mini- tuttle box would be best, it goes thru the hull with 1 bolt. If you use a surf base system, my research found the Probox best suited. Futures next and FCS NO but very popular with surf boards. Their are others as well. Fins pretty much just fit that particular box. quite a range of fins available, unless I used a mini-tuttle or US box I would not go longer than 5" for the 2 fins. About half the advisors I have recommend tying the box system into the underside of the board, I plan to follow the Probox instructions, which don't. The tri fins seem to work better with a swallow tail.
the mini-tuttle is used by some wave directional kiteboards, Best, Slingshot, Cabrinha.
and zero cant .
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good winds

Last edited by carvesalot; 19th February 2009 at 12:50 PM.
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