Hi all,

Just want to share a project I've been working on recently with the windsurf community here. I've had an idea for a while to convert a formula board to be able to take three weed fins to allow sailing in shallow waters and weedy conditions. The concept is mainly for fun sailing in very light winds and in areas on the lake where I normally sail (Lake Illawarra) that you couldn't normally access on a formula setup. Was also interested in how it might still work course racing in weedy conditions for example, or maybe with outboard straight fins in a twin fin setup. Would be very versatile anyway, once the boxes were in.

Did a lot of research but couldn't find much info on this kind of thing. Did find some stuff about a twinfin formula and noticed some similarish projects here on seabreeze which I got some ideas from. Decided in the end to install two powerboxes perfectly parallel to the centreline into a fanatic falcon tt05 formula board that I had, the underwater shape of which lent itself well to the trifin setup (see photos). Did the installation (a first for me) over christmas mainly, and have tested the setup three times now in different conditions.

I put together some footage from two of the sessions below. It all worked as good or better than I'd hoped. Gets up and planes very early. Interestingly it still rides flat even with me using the footstraps in the usual outboard positions. Plenty of drive and not a hint (ever!) of spinout. Really fun to go hammering through glassy water in the primbee shallows with a 10.6. Have only really tested the three weed fin combo pictured below so far. The fins are about 27-28cm. The whole feel of the board is still very much like a formula board (understable I guess) and while it gets upwind respectably, its definitely not as good as proper formula, prob more like a good slalom setup. I've raced it pretty successfullly against raceboards in an 8-18 kt NEer. Lots of potential for more testing of different fin arrangements/sizes, eg like three deltas :)

Here's some photos/videos of the process and finished product:

Thanks for sharing John love seeing people modifying equipment

Great mod and looks like it works a treat. next stop Lake George

Great idea, a lot of flat areas are weedy and shallow. Well done.

Wow that's awesome! Well done!

Great stuff John. I reckon the weed fin on the right is what makes it work!!
Good vids!
Must have a go soon.

Awesome!

I have the same board and have thought about doing the same sort of thing, but as usual, I am lazy and never got around to it. Good to see it works.

Has anyone got any thoughts about running two fins in-line? I.e. adding a finbox in front of the existing one and run two similar fins?

Will that give me twice the lift, or will they interfere with each other.

I have two hifly madd boards, which are twin-fin, and its quite easy to get one fin to spin-out while the other one is tracking fine. I figure that's because they are probably slightly underfinned. Your tri-fin avoids that and still gives around the same fin-depth. Good work.

great videos too

Great idea and the videos were excellent!

Great video presentation
Great idea, now I have a winter sort of project to play with so can use it at the Mandurah Estuary

So I'm interested in how it foot steers with parallel fins? My twin fin ground effect thingoe, didn't foot steer well at all until I toed the fins in a couple of degrees. It still doesn't feel right so I've added a 3rd central fin, but haven't tested that combo yet.
But I am using very highly raked delta style fins, about 60 degrees from memory, that may be part of the problem.

It's very encouraging to see you've got the concept working though, great stuff! I'll have to do some more testing with mine.

It footsteers fine decrepit, no different to normal formula, might jibe slightly better. I did see the thread on your project and I was worried I might have the same problem.

Could be the centre fin makes all the difference, I'll find out soon.

Nice work , mini tuttle boxes ? I had thoughts to make a Formula a twin, but never did.

I need a board for shallow waters, and shore line rocks, so I turned this Tabou Rocket 135 into a tri, using 2+1 fins, it is slightly slower both to plane and speed but it turn like 100L. Works really well.

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I also made my own BLACK BOX.

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