HI Newbie to foils, is the standard Tuttle box on a windsurfer strong enough to take a foil? Wanting to try this out before spending up on a foil board. Cheers Bob

This is a giant topic, but... A deep tuttle? What's your risk tolerance? It might be OK to try. But, you could definitely break the box, so use a leash on the foil and be aware you're risking breakage. There's maybe less risk if the foil has a flange.

Yes, if you search these fora you will see a ton of commentary about tuttle boxes.

In general most deep tuttle boxes that reach all the way from the bottom skin to the top skin are fairly strong. Prior to foiling, finboxes were designed and stressed to carry side loads. Now with foiling you have to factor in fore and aft loads exerted by the front wing being in front of the strut. Pre-foiling deep tuttle boxes have been known to fail this way, but such failures are not common.

If your pre-foiling tuttle box has those wells (or "chimneys") on top, in order to use shorter screws, I contend those are the worst case of potential failure for the box. If, on the other hand, the box goes all the way through from bottom skin to top skin, such as what we had on most of the better formula boards, the box is much stronger.

All that said, if you mount a foil with a flange (such as Slingshot), you can stack the deck in your favor to avoid a failure. If your box has those chimneys, I recommend you make a big rectangular "washer" that covers the entire top of screw area to spread the load to the top skin (where it belongs).

And use a leash.

Thanks for all that, it's really only a stop gap arrangement to see if the foil I'm making will work then I guess I'll build a designated board. I was thinking of filling those little tunnels with epoxy and drilling them out to spread the load, also will fashion a flange of sorts or more a "plate" really. The other option was to make up a plate that fit a quad or twinfin set up but those boards are all sinkers so have gone with the tuttle board. Just needed to know what the likelihood of destroying the board. Cheers for the info. Bob

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used2surf said..
Thanks for all that, it's really only a stop gap arrangement to see if the foil I'm making will work ...

There are enough used foils now on the market that unless money is super, super tight you chase one down. Foiling is hard enough without you also being test pilot on a prototype. The board you can can cobble together but getting all the dimensions right on a foil will be challenging, especially if you don't know exactly what it will feel like if it's correct or incorrect. Just to name a few: fuse length, wing placement vs the foil mast, stab angle, stab size, foil rake, wing size, proper mast stiffness. It can be done - just that it's the hard way to get from Point A to Point B on the learning curve.