Whatever get's the front foil between your feet when the board just starts to lift.
Different foils have different mast to COE of front wing.

mcrt said..
Takuma and Fanatic foils have the center of lift further in front of the mast so their boxes are further back.

Depending on what foil brand you are going to use i would get a bottom pic of the boards by that same brand and determine the box position.
I would measure this on a picture of a board with a similar lenght to your build because longer boards tend to have the boxes further forward.

Way more logical than my comment as being in a stupid mood, I was going to suggest underneath the board.
This is not a silly as it seems now we have handles top and bottom.

Pacey said..

Slyde said..
I'm going to start a new build v soon. All my previous builds have had the fin boxes a reasonable distance from the tail, the rationale being that the balanced position you stand on the board to start is the same as the foot position when foiling, and it decreases swing weight by placing your body weight closer to the nose. But I notice Fanatic have chosen to put their foil boxes closer to the tail, but they are the only brand i see doing this. Has anyone any experience of riding the fanatic boards compared to other brands and can comment on whether this is a good idea or not? Do you end up having to move your feet back every time you start foiling? Or Have Fanatic compensated for this with a very thick tail??

I've got a fanatic sky wing 6' and I feel that for my weight (94kg) the foil tracks and foot straps are too far back, and there has been too much volume taken out of the back end, particularly with the heavy deck concave under the rear foot. I'm in the planning stage of building a new board inspired by the shape of the fanatic, but with more volume aft, and the tail bevel and therefore foil boxes further forward.

Too far back for what foil?.
Until manufacturers start giving data about foil and board sweet spots (if they ever do) mixing board and foil brands can turn out badly.

Rocker is another factor, the Progression Project guy had to shim his Takuma Kujira to get it riding ok (for prone surf).

mcrt said..

Pacey said..

Slyde said..
I'm going to start a new build v soon. All my previous builds have had the fin boxes a reasonable distance from the tail, the rationale being that the balanced position you stand on the board to start is the same as the foot position when foiling, and it decreases swing weight by placing your body weight closer to the nose. But I notice Fanatic have chosen to put their foil boxes closer to the tail, but they are the only brand i see doing this. Has anyone any experience of riding the fanatic boards compared to other brands and can comment on whether this is a good idea or not? Do you end up having to move your feet back every time you start foiling? Or Have Fanatic compensated for this with a very thick tail??

I've got a fanatic sky wing 6' and I feel that for my weight (94kg) the foil tracks and foot straps are too far back, and there has been too much volume taken out of the back end, particularly with the heavy deck concave under the rear foot. I'm in the planning stage of building a new board inspired by the shape of the fanatic, but with more volume aft, and the tail bevel and therefore foil boxes further forward.

Too far back for what foil?.
Until manufacturers start giving data about foil and board sweet spots (if they ever do) mixing board and foil brands can turn out badly.

Rocker is another factor, the Progression Project guy had to shim his Takuma Kujira to get it riding ok (for prone surf).

Issue is that it's too far back for the centre of bouyancy of the board in displacement mode. There is a misalignment between where your centre of gravity needs to be when you are kneeling, standing in displacement mode and standing when foiling. Ideally these should line up, and on the fanatic they don't.

the fanatic is a great board when you are powered up in displacement mode, or when you are up on the foil, it's when you are kneeling or standing without much pressure in the wing that is not ideal, and I think the issues can be relatively easily fixed

OK thanks, that pretty much confirms my suspicions that Fanatic have not put their boxes in the best position. I wont be going down that route for now. BTW the comment about rocker is very true. I find a plate shim has become essential and my future boards will have more rocker as there can be a tendency for boards with not enough rocker to ride nose down which is not good for foot pressure distribution.

MidAtlanticFoil said..
Kinda off-topic, but the mcrt's comment makes me think of the America's Cup 'boats' down in NZ right now. Their hull designs are taking into account all kinds of factors, one of which is early lift-off. I hope some wing board builders take inspiration from some of their radical design concepts.

The hull designs are pretty radical and some are quite different from each other. Some have a a long exaggerated keel running the length of the center of the hull. This is to keep the aerodynamic pressure gradient from the sails intact throughout the whole rig, by not letting air transfer beneath the boat, causing a loss in efficiency. They are going to try and run the boats as close to the water to exaggerate this effect. (This design feature doesn't translate to our craft, but interesting nonetheless)

Difference is that the AC boats are long and slender, which means that they want to minimize drag from the hull at intermediate lift fractions (lift fraction is the proporion of the boats weight that is being supported by the foils, 0.0 is no foil contribution to the lift, 1.0 is fully flying with the hull clear). So the New Zealand boat, which looks like the fastest so far, has quite a rounded shape to its keel or skeg. It's not trying to generate planing lift from that part of the hull, because that can be generated at a far better lift to drag ratio by the foils. This means that the boats go directly from displacement to foiling mode.

on a wing foil board, we dont have much waterline length to use to get us up to foiling speed with low drag, so we need to rely on a little bit of planing lift from the hull, and we can pump a bit to help get it onto the plane. This means we go from displacement mode, to planing mode then to foiling mode, even if the planing mode is quite brief.