Foil mounting thoughts

grantmac · Post by **grantmac** » Sun Aug 13, 2017 10:58 pm

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 wing. 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 fins 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

winddude · Post by **winddude** » Mon Aug 14, 2017 8:34 am

My concern with the four bolt system would be drag from the plate on the bottom before you get on the foil. And if it's one of those 3m sticky plates I would be worried about it peeling off or delaminating the board over time. honestly it seems really stupid too me.

nanmoo · Post by **nanmoo** » Mon Aug 14, 2017 10:21 am

Drag from the bolts is minuscule compared to the drag from the board itself. I think Juandesooka proved the thru-bolt concept already.

winddude · Post by **winddude** » Mon Aug 14, 2017 10:29 am

not the bolts the actual plate. That looks like a lot of drag to me, and remember this is on a windsurf not a silly kiteboard. On the kiteboard the drag isn't an issue because the kite pulls you up and out, the windsurf foils you still need to generate board speed.

I would go the route of replacing the fin box, the cost isn't a lot if you tackle it yourself, the labour isn't that much a few hours, but you just have to wait for epoxies to harden etc, that adds to the total time.

nanmoo · Post by **nanmoo** » Mon Aug 14, 2017 10:42 am

Same point stands. That whole mount causes very little drag at the speeds it will be travelling before you get on a foil. Put you hand in the bath tub sideways and slice through the water, you'll see. The sail generates a lot more force than your shoulder.

winddude · Post by **winddude** » Mon Aug 14, 2017 10:47 am

Ignoring the kiter...

Also not sure why you want to move the box forward, starboard is running the box in the exact same spot on the foil board as they do on the iSonic slalom board... in fact i've heard they are nearly identical boards and shapes.

winddude · Post by **winddude** » Mon Aug 14, 2017 10:49 am

nanmoo wrote:Same point stands. That whole mount causes very little drag at the speeds it will be travelling before you get on a foil. Put you hand in the bath tub sideways and slice through the water, you'll see. The sail generates a lot more force than your shoulder.

Try taping a dinner plat to the bottom of your board next time you go windsurfing. See how easily you plane. As soon you pump to get on a plane you'll probably spin out.

nanmoo · Post by **nanmoo** » Mon Aug 14, 2017 10:56 am

Ok I'll totally do this if you supply the dish - and it won't matter much - but to be fair the foil also helps you plane sooner, with less drag on the plate, and once you are foiling at all the dinner plate does nothing.

winddude · Post by **winddude** » Mon Aug 14, 2017 10:58 am

nanmoo wrote:Ok I'll totally do this if you supply the dish - and it won't matter much - but to be fair the foil also helps you plane sooner, with less drag on the plate, and once you are foiling at all the dinner plate does nothing.

Done, I'll even bring the tape!

grantmac · Post by **grantmac** » Mon Aug 14, 2017 11:18 am

That stick on plate is a triumph of laziness and marketing over hydrodynamics and engineering. Was not and never will be an option.

Moreover retaining performance without the foil is a high priority. Hence why I'm not doing mast tracks either. I'm concerned enough about four small holes let alone two gaping tracks.

With regards to fin box position:
Most starboard boards put the forward bolt of the tuttle head centered in the rear footstrap with the strap in the rear position.
Slingshot goes a but further forward centering the box itself.

If I did a direct replacement I'd have that bolt in line with the rearmost strap insert. That makes it ride way too back footed.

winddude · Post by **winddude** » Mon Aug 14, 2017 2:12 pm

Have you tried a lower boom, longer lines? Moving the mast forward to reduce the back foot pressure? Closing the gap, and rig tuning. These might be easier to address the back foot pressure than moving the fin box.

grantmac · Post by **grantmac** » Mon Aug 14, 2017 2:56 pm

Doesn't tune AT ALL like a regular board. Virtually zero foot pressure across the board, it's all vertical. Mast actually goes back to reduce back foot pressure (already at max rear). Boom is run pretty darn low and frequently you just cruise unhooked once you are up.

winddude · Post by **winddude** » Mon Aug 14, 2017 3:46 pm

Curious what size sail you are on? A few guys at nitnat this weekend were having good success with 7.0 and 7.8 race sails on foils, maybe only a few knots less then they would with the same size sail on a slalom board.

Looks like most of the race style foilboards have the box in the same position as the starboard, where as slingshot and naish, the more recreational foil boards have the box centred under the foot strap. Which makes sense and goes with what you are saying. Smaller sails you won't be powered, and need a narrower stance, and closer position, where a traditional slalom board would be setup for a pretty wide stance, with the mast track further away, setup for a bigger sail.

Longer lines will let you transfer some of that power into the boom even when under-powered and even out your stance by letting you move around more.

grantmac · Post by **grantmac** » Mon Aug 14, 2017 5:42 pm

5.7-8.5 with a 7.4 RAF being my most used.

MBP doesn't really work the same as a regular board. Neither does center of effort. Having the mast base forward with a large sail just sticks the board to the water. So does having the front foot too far worward. Both force you to keep a lot of weight on your back foot in order to keep the center of gravity over the center of lift. Maintaining that balance is absolutely the most critical thing.

It would be much easier with the weight biased towards the front foot which is how most foils are designed to be used.

winddude · Post by **winddude** » Mon Aug 14, 2017 7:01 pm

I don't know i only foiled for <30 mins, but picked it up in a tack and was under sailed and thought longer lines would have helped me, i still found closing the gap helped. should be a lot like formula or slalom where you are primary on the fin, and moving the mast forward will help you close the gap in lighter winds, which results in moving the CE back which then allows you to drive more through your front foot.

I found it a lot like trying to hold a board on a plane when you are under-powered.

Foil mounting thoughts

Foil mounting thoughts

Comments

Session Logs

Posts

Wingfoil

Windsurf

Kitesurf