View Full Version : Turning a Evo 75 into a twinfin

2nd August 2009, 03:20 AM
Hi there,

Since September '08 I have Evo 75 XTV 2008. I am/was new to wavesailing so I damaged the board quiet a lot in the past time by bumping into rocks, getting washed in shallow breaks and crashing jumps (north Fuerteventura is great for your material...). Now I discovered some damage to the finbox and the surrounding area on the bottom of the tail. A friend of mine had a really nice idea: would it be possible to remove the finbox, fill up the gap and make it a twinfin?

I really like this idea, but it does rise me some questions:

-Is the shape of the evo able to work with two fins instead of the orginial single fin setup?
-If not: what kind of changes does the boardshape need to work with a twin setup?
-Where would be the best place to put them (I understand that it should be somewhere in the same area as the orginal finbox)?
-How will the fins influence the character of the board?
-Since I'm only 65 kg the board is quiet big for me and in big waves and highwinds I can't maintain control in bottumturns and I don't have enough weight to put pressure on the frontfoot/rail (especially around the mastfoot I think the board is too wide/fat for me and forces me to turn on the backfoot), will a change from single to twin improve my control in the bottumturn?

I hope you guys have some usefull input for me!

Best regards,

3rd August 2009, 03:48 PM
Wow Stefan, your Evo must have 9 lives! Could be an interesting project!

I guess your best bet is Ola as he has been thinking about converting His E70 2007 into a twinfin/thruster set up. If he hasn't allready done that he might have at least some ideas.

Another good read is this thread on the boards.co.uk forum, where chrispavlo converted and Acid into a Twinfin: http://www.boards.co.uk/forum/forum_posts.asp?TID=24230&KW=conversion&PN=0&TPN=3

Good luck with the broken foot.

4th August 2009, 04:28 AM
I'm thinking about the answer..back tomorrow.

6th August 2009, 05:16 AM
OK, here goes:

IN general, when tuning a certain shape to a twin fin, you do need to tweak it a bit for things to work perfectly. For example, it seems twin fins require slightly beefier rails around the footstrap area if you still want to be able to put power down in your turns. Often outline is tweaked too. When the ETs were first designed, they came from EVOs but rails are changed and outline tweaked so the board would still go vert well. But compared to many other boards I think the difference are maybe smaller, ie an EVO would work reasonable well as a twin. And the fact that you're a lightweight that rides a big board say that it might work better than if the board would have been relatively small.

If you like to make it a twin, I would place the boxes 13,5 cm apart (center to center). and put them so that the front of the fin boxes are right under the front screw of the back footstrap, possible a cm further forward (fine tuning depends a bit on which twin fins you're gonna use).

Another option is to convert to a thruster or even a quad. Then I would use the minituttle boxes in the front. They are easier to install than two new us-boxes for a twin conversion.

The thruster option (in my opinion) is maybe less interesting if this is gonna be your smallest board since (at least when I've don it) it has sort of powered the board up and made it feel bigger. Based on comparing quad and single (Quad 71 to EVO 70 - same shape, afaik) I would say the quad conversion tends to leave the "size feel" as is. With Quads I would go with future boxes for the rear. The EVO70=Quad 71 goes really well as a quad and I would imagine the 75 would do too. Tell me if you want some beseline measurement for a quad of thruster conversion.

6th August 2009, 05:07 PM
Hi Ola,

Thanks a lot for your reaction, I think this really helps! The EVO will not be my smallest board, I have an old 70 litre sailboards tarifa highwind (more classic shape) and an AHD classic wave 68 (which is pretty much ready to be thrown away). Here in Holland I do think that de EVO 75 will be my most used board because of the onshore and gusty conditions. What will be the biggest difference between quad and twin in these conditions (let's say 4,7 and 5,2 winds and 2 to 3 metre waves)? Point is that a friend of mine does me a favor by repairing my boards, and I don't want to give a lot of work because he does it in his spare time. Do you think I can also first try twin and if I want to convert to quad later on I just put two mini tuttles in? Or is the location of the rear fins of a quad different then the position of a twin (I can imagine the rear quadfins have to go further back)? If you could send some baseline measurements of the quad setup I would be really happy, my mailaddress is stefan_2511 [at] hotmail [dot] com. Thanks again for the useful info!

Kind regards,


7th August 2009, 04:04 AM
"Quadifying" a twin can be done, many quad experiments work like that and usually with smaller fins in front. But the Starboard Quads are a bit different and if you wanna go by the fin setup on the Quad 71 (the closest to the EVO 75) it will not work. ON that board the rear fins are only 105mm apart (c-c) which is to close for a twin. The center of the rear fins are 183mm fromt he tail and the center of the front boxes 340mm from the tail, exactly level with the rear option of the back strap front screw (a good guideline for the front fin center, I think). The (back of the) front fins are 47mm from the rail (the actual rail, not the tucked under line).

If you start with twinsers, maybe you can put them 130mm apart and then not too far forwards (say with the front right under the front plug for the back strap, not further forwards). Then you could probably quadify it later and runt the rear fins right at the back of the boxes.

7th August 2009, 11:24 PM
Hi Ola,

Thanks again for the information! I will talk to my friend and keep you up to date about it!