Foil mounting thoughts

grantmac017 · Joined: 04 Aug 2016 Posts: 946

Info upfront: my budget is near zero and I'm into DIY.
I currently foil using an older formula board with a DT box using the Slingshot with bigger wind. Works well enough but not optimum since the fin box is a little too far back and mast track a little too far forward. This results in it driving mostly off the back foot. Very comfortable and nice around a course but not in the spirit of why I got the foil to begin with.

Looking at the boards which slingshot designed I went out and got an older cheap board that was similar in specification.

Unfortunately everything in that size range is powerbox so I need to come up with a mounting solution.
The powerplate is a non-starter. I don't trust a single 1/4" bolt to withstand all that force.

Converting to DT is an option but it's very labor intensive.
Pluses are that I can shift the fin box forward (this board could use it) and it would be cosmetically nice.

The second option I'm considering is doing a kite style 4 bolt arrangement. This will let me get the best position for the foil while still using PB fi s for regular use.

What I'm wondering is how much those mounting holes will ruin the performance of the board. Am I over thinking this or would some flush set screws fix the problem? Is it even an issue?

Thanks,
Grant

westender · Joined: 02 Aug 2007 Posts: 1288 Location: Portland / Gorge

If you convert, do the Naish thing. 2 mast tracks for the 4 bolts. Lots of adjustment??? That's what I saw yesterday???

grantmac017 · Joined: 04 Aug 2016 Posts: 946

I thought about that but I'm pretty sure it'll ruin the non-foiling performance of the board (which is actually quite nice for $120). The Naish is not really designed to windsurf off the foil and SUP speeds are low enough I doubt it would matter.
Also I'm not totally sure that it will be strong enough unless I add a stringer up to the top deck of the board and at that point why not just go DT? There have been a few ripped out from what I've seen.

Just had a weird thought: I wonder if you could make a longer DT box that allowed forward and back trim? Would likely need pieces to seal off the openings front and back, plus have to be built like a tank. But could be a really neat concept.

Worth messing with somewhere way in the future.

isobars · Joined: 12 Dec 1999 Posts: 20935

I've been hearing from multiple sources including shapers that unless a board is built from the get-go to withstand the stresses of a foil, it won't survive more than a few hours (some say minutes) with a foil stuck up its finbox, even a deep Tuttle. Plan for a disaster, hope for success.

grantmac017 · Joined: 04 Aug 2016 Posts: 946

While I'm sure many boards will not last when coupled to certain foils (cobra boards and foils without flange heads), in this particular case I'm not concerned with the durability of eother option.

I'm talking entirely about the hydrodynamic vs. effort trade off.

nw30 · Posted: Tue Aug 15, 2017 4:26 pm Post subject:

The only time you really need to worry about performance is when you're up on the foil, most foil boards I've seen have bolt heads and edges of plates being not flush with the bottoms, and it doesn't seem to effect the performance.
When converting a standard board to a foil board, you absolutely have to use some kind of plate, even if you make one from scratch with 1/4" aluminum stock, otherwise you could end up with something like this~

dllee · Joined: 03 Jul 2009 Posts: 5329 Location: East Bay

A blessing in disquise!
Half the work is done for you! You only need to smooth out the rough edges, reinsert the fin box, add woody spider legs, and reglass the top and bottom.

grantmac017 · Joined: 04 Aug 2016 Posts: 946

Ive seen that picture before. Looks to be a non-sandwich construction SUP with very thin glass too and bottom that somebody stuck a DT box in with a bit of thickened epoxy.

My concerns about the hydrodynamics aren't in reference to using the board with the foil, I know there will be little effect. Heck you can barely notice s bunch of weeds.

I'm wondering what effect the mounting holes will have when sailing with a regular fin. Will just screwing in some set screws solve the problem or am I likely to create a dog of a performer?

westender · Joined: 02 Aug 2007 Posts: 1288 Location: Portland / Gorge

I'm fine with using packing tape over any unused boxes or holes.

SupSURFmachines3716 · Joined: 11 Apr 2016 Posts: 17

That failed box was due to melted EPS. The owner admitted he just screwed up using fast kick hardener. So dismiss that post.

Have you tried moving the Slingshot wing forward by mounting the fuselage more forward on the bottom of the mast? That solves the issues you're having. My friend had the same issues with his board and the Slingshot foil. Moving the fuselage made it work much better.