I’m thinking about converting a 95 lt Naish Wave board from single to thruster. I like thruster better than single and currently I have a 112 lt RRD FIREWAVE thruster. I can’t justify spending over $1500 in a board I won’t used that much. I rarely used the 95lt but I like to keep it handy for very windy days.

Any advice; is it worthy; where to get fin boxes; angle/cant; etc?

Greg from Sheb is your guy to weigh in on this. Look at his work in this thread.

windsurfillinois.com/index.php/forum/win...ace-a-broken-foilbox

If you go for it, I would use finboxes that allow some fore/aft adjustment (US boxes?). You don't have the luxury of knowing exactly where they will work best, so having some adjustment will increase the chances that you can find the sweet spot.

A little toe-in is standard on thrusters, maybe 2 degrees. Too much and you'll just create a bunch of drag and go slower...

The US finboxes I used when I built a few wave boards (late 80s) were Chinook, and they had a solid "post" that was long enough to stick out of the deck (you would saw it off flush after it was glassed in). That made it extra strong. I don't know if they still make those or not. I've never put a finbox in EPS foam, so I don't know if there's ways to reinforce the area around the box (like woodies).

Should be a good winter project
Drew

Thanks! I'll take a look

Thank you the advice. It totally makes sense using US boxes.

How about getting a used board that already has what you are looking for? Would be easier and potentially cheaper than messing around with that Naish.
But if you really want a project, then you will need to be accurate in the process.

3 options:

1 - you keep the stock Powerbox insert and just install side fin boxes (Mini Tuttle or Slotbox). That’s the combo used by Goya for their Goya One Thruster 95. That way, you still have at least a functional board in case you don’t like the way a thruster setup behaves (can use a blind insert) and you are also saving yourself top deck rework. The downside is that you’ll have to decide the kind of riding you want: for a more turns or looser feel place center fin leading edge in line with side fins trailing edge. For more drive, place side fin a bit more forward (like on the Goya One - check their web page).

2 - you install short USbox as side finbox. That way you’ll have a bit more flexibility of fin setup but a portion of the slot will remain open and exposed (not preferred, not great hydrodynamic).

3 - you remove the powerbox and install a US finbox plus 2 side boxes (Mini Tuttle or Slotbox). That’s a bigger surgery that will mess up the deck but at least you will be able to adjust the center fins position (preferred).

I’d go with option 1.

As far as placement and dimensions I didn’t find a lot of Windsurfing-relevant info. Maybe you could copy and enlarge 1:1 a picture of a Starboard Kode or the Goya One 95l.

In most cases, the side boxes will need to have a toe-in (inward angle) of 1/8” to 3/16” (to be verified). Also the side boxes can be placed about 1.25” away from the edge of the board at its closets point, if you have the thickness necessarily near the rails (measured from the outer lower corner of the side fin slot). Also to be verified.

Anyhow, that’s a relatively involving amount of work. If you never did epoxy and fiberglass work like that before, I highly suggest you look at similar how to’s on YouTube (ie surfboard making). Good luck.

Greg,
Thanks for the suggestions. It´s a US box, and I will being inclined to use short USbox as side finboxes because it will give me some room for adjusment if I don´t get it right like Andrew suggested. I guess my biggest concern will be get the right inward angle and the fins cant, which in the worst case scenario I can just remove the fins, burt at least I earned some experience. By the way, I had done some major nose repairs on my boards.
You´re righ about getting somethin used. The problem will be finding one at a reasonable price and in a descent shape. For now, the Naish makes for great decoration in my basement.

There are many ways to do the job, but I wouldn't install more US boxes for side fins: If you already have a US box long enough that allows your center fin to be adjusted forward or back, you just need to install fixed side boxes at the right distance, slightly overlapping the US center box and with the proper toe-in.

For more on Toe-in check this article:
www.k4fins.com/2016/06/22/toe-in/#:~:tex...0%9D%20Nick%20Carrol.

For reference, my 109l Kode (With pictures):
• Side box outer lower edge is ~1.3/8" away from the rail.
• The toe-in is ~1.5 to 2 degrees. (I would suggest putting less than more cause your board is not a wave board and putting lots of toe-in will slow you down).
• Back edge of side boxes overlaps front edge of center box by ~1/2".

Not sure I understand what you call "fin cant". But just in case, you do not need to put any extra vertical angle to the side fins. Since most boards have a slight Vee in the back, your fin will be angled properly if you just install the fin box "normal" to the surface of the board. See what I mean? Good luck.

Thanks for the link and the suggestion. I will compare my Firewave 112 (thruster) and yours and go from there. One thing, The Naish is indeed a wave board. "Wave" is actually the name of the board. More about the board here: www.naish.gr/boards/6642-3584-wave.html.
This link below from True Ames explains fin cant, but I think you got the idea. I will post when I have a chance I picture of the fin in my thruster. The side fins are not US box, more similar to yours, but they do allow for some small adjustments.
www.trueames.com/pages/fin-terminology#:...%20flow%20of%20water.

And here's the man himself riding Jaws in 2021 on a single fin Naish Pro Wave from 2008

Happy to see you found all the answers by yourself. Have fun with the epoxy work.