Foil Setup: Front Wing Placement

Isn't it curious how sometimes things can be easy and confusing at the same time? Setting up equipment for windfoiling can be that way. The general rule is simple: "you want the front wing located as close to the center of your stance as possible", the Slingshot manual says. Sound easy, right? Let's look at a few examples, starting with Nina's foil setup:

This is her old Skate 90 freestyle board and the Slingshot Infinity 76 foil with a 60 cm mast, the gear she uses for foiling 90% of the time. She can foil on this in 12-13 mph wind with a 5.2 m freestyle sail, with very good control. She's also foiled through a few jibes, and started on duck jibes and 360s. Let's zoom in a bit:

I placed the ruler close to the middle of the front wing, where the "center of lift" (COL) is. If you compare it to the position of the foot straps, you can see that it is close to the middle, just a bit towards the back strap.

Now lets look at another setup that does not work nearly as well:

This is my Skate 110 with the Slingshot Infinity 84 front wing. It's shown with a 45 cm mast, but ignore the mast size for the time being. Here's a zoom-in:

You can see that the COL is much closer to the back strap. When I tried this setup (with a 71 cm mast), it was hard to get up on the foil, and felt very unbalanced once up. Nina tried it, too, and came to the same conclusion.

What's the difference? In both setups, the foil is mounted in the "C" position on the fuselage, which put the front wing closest to the front. However, my Infinity 84 wing is significantly larger than Nina's i76. All the extra area was added to the back of the foil, which moved the "center of lift" back by about an inch or two. In addition, Nina is using the Powerplate to move her foil forward even more:

You can see that the Powerplate here moves the mast forward by about 2 inches. In total, the COL for Nina's setup is about 3-4 inches further forward than for my setup!

So the obvious thing to try is to move the front wing for my setup further forward. I did this by drilling a new hole into the fuselage exactly 2 inches behind the rear hole for the "C" position. By using these two holes, I now have a "D" position where the front wing is moved forward two more inches:

You can see that the COL has moved forward to be closer to the middle of the foot straps. When I tried this setup, it worked a lot better. The foil came up a lot earlier, and it felt more balanced when up. But please note that the extra hole weakens the fuselage, and that the larger distance makes it more likely that the fuselage will bent! So I'm not recommending that you copy this approach!

When I replaced the powerbox in my Skate with a foil box, I put the foil box at the same position that the powerbox had been in. I actually had tried to use the Skate 110 for foiling before, and it had worked well enough - but I completely forgot that I had used the Powerplate, which moved the foil forward! In hind sight, I should have just added a couple of US fin boxes to the Skate 110 for use with the Slingshot pedestal mount. Adding the tracks so that they partially overlapped the powerbox would have been easier than using the foil box, and given me some adjustment room (in addition to the option to mount the mast in the A or B position). That would have made it easy to fine-tune everything for a perfectly balanced setup.

One thing that perhaps let to my confusion about the box placement is that the "C" position works very well with my slalom board:

I don't use foot straps on this board for foiling, so I placed booties where I usually put my feet. The back foot is usually all the way back against the strap that I use to attach a safety line to, and the front foot placement varies a bit depending on conditions and power. But it is easy to see that the distance between COL and back foot is more similar to Nina's setup than to my "unbalanced" setup shown in the second picture.

A closer look at the footstrap placement on the different boards reveals a significant difference: on the slalom board, the back strap positions are about 2 inches further back than on the freestyle board. That's true for the boards shown, but also for several other (newer) Fanatic slalom and freestyle boards in the garage. On some foil boards like the Slingshot Wizard, the back straps seem to be even further back, so that the back foot is where the mast is. Here's an image of the Slingshot Wizard 125 with the foot strap position highlighted:

For comparison, here's an image of a typical freeride board:

The back footstraps are several inches forward of the fin / foil box, similar to what we saw for the Fanatic Skates.

So, if you'd want to use a Slingshot Infinity 76 foil with a Wizard 125, the consensus is that the mast should be in "B" position on the fuselage. For use with a typical freeride board where the footstraps are further forward, the mast has to be in "C" position for the i76.

For the Slingshot Infinity 84 front wing used with a Wizard, the foil should be mounted in the "C" position. This means that use with a freeride board would require a "D" position! Since the fuselage does not have a "D" position, anyone trying such a setup will likely be disappointed (or has drill an extra hole).

Interestingly, Fanatic has chosen a more forward footstrap position for their foil freeride board, the Stingray:

There are lots of option to mount the rear straps, but all of them are pretty far forward. This makes sense, since Fanatic also sells several "foil ready" boards with similar strap positions. All these boards need to work well with the Fanatic foils. Compared to the Slingshot foils, the Fanatic foils have the front wing mounted further forward (the mast is further away from the front wing), which is necessary for a balanced setup.

If you buy a matching foil and foilboard from the same brand, this is not an issue, since you should be able to simply follow their setup instructions. But it you try to "mix and match" foils and boards, subtle differences like a 2-inch variation in the footstrap placement can make the difference between a setup that works beautifully and a setup that is barely useable. Similar issues arise from the position of the foil on the fuselage. For example, RRD freeride foils have the mast mounted close to the middle of the fuselage, while the Slingshot Infinity foils have the mast closer to the front wing, even in "C" position.

For board conversions, some of these problems should be avoidable by going the mast track/pedestal mount route, especially for Slingshot Infinity foils. Whatever option you choose, though, I suggest to check where the front wing will end up before you start the router!
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I have contacted Slingshot with a suggestion to add a "D" position to the fuselage, and heard back from Wyatt Miller, their windsurfing guru. He said moving the mast further to the center increases the chances that the fuselage would bent, since it has more leverage. Nor does it help that the extra hole weakens the fuselage! Apparently, jumping with the larger front wings (Infinity 84 and 76) can bend the fuselage even in B or C position, so Slingshots suggests to use smaller front wings for jumping and things like loops. I had actually noticed a bit of new instability when using the "D" position, but the i84 is always sensitive to water movement caused by chop and swell, so it's hard to tell if this was caused by increasing the distance between wing and mast. To be on the safe side, I'll add a track mount to my Skate.