What is the distance from the center of the sail mast base to the center of the front screw hole of the DT box on the deck of the board?

For my AFS W95 foil with F1080 wing on a Goya Bolt 135 the measurements are:
foil mast leading edge to wing trailing edge 18.5 cm
foil mast leading edge to wing leading edge 35 cm
sail mast base to DT box front screw hole 108.5 cm.

That foil is just balanced on that board. For your foil/board you would need the sail mast base to be ~7 cm closer to the DT box than for my board, I think, so around 101.5 cm.

Thanks for the replies!
I will check those measurements when I will be able to access my gear. Currently I am inland and my gear is at the sea :-(

To bad manufacturers don't list these it would make it easier to get and idea of gear compatibility, even if in real life things are a bit more complicated and interdependent. Not everyone can just buy and try many pieces of gear to arrive at the best combination by trial and error.

Sandman1221 said..
Your JP Hydrofoil is a foil board so the mast track will be farther back and the DT box will be farther forward.

I hope so because last time I was looking at those measurements I think my conclusion was that the footstraps won't go as far back as it would be needed to get the front-wing in the center between them.
So it seems that the need to move the mast-foot far back is not uncommon, at least I'm probably not doing it completely wrong.

I was also thinking about doing some photogrammetry to measure stuff. Using marketing images might be inaccurate because sometimes they are just symbolic.

That line on your JP is pretty close to where the center of my wing is on the Bolt. But I removed the rear foot straps because they are not back far enough for when I use back foot pressure to get foil to lift board. But once up move foot farther forward.

But mast track position is the other part of the foil balancing equation, the JP mast track looks like it is farther back than the Bolt, expected and good.

Mushin said..

Sandman1221 said..
That line on your JP is pretty close to where the center of my wing is on the Bolt. But I removed the rear foot straps because they are not back far enough for when I use back foot pressure to get foil to lift board. But once up move foot farther forward.

But mast track position is the other part of the foil balancing equation, the JP mast track looks like it is farther back than the Bolt, expected and good.

Good to know! Maybe it's not absolutely necessary for the wing to be dead center between the foot-straps. If needed the cheapest fix would be to buy a bigger fuselage I guess.
How does your backfoot position change when going upwind, downwind or sailing on a reach?

You definitely do not need wing dead center between foot straps, in fact that position may be too far forward. I do not use a rear foot strap, so can't tell you where it is exactly, sorry!, but it is always somewhere on the rear pad where the rear foot strap is mounted, see picture of my Bolt under General topics, "Goya Bolt Black to White-----".

I was told by the guys at BigWinds that I would put the rear strap back on, but that has not happened yet. And when doing a foiling gybe it really helps to not have a rear foot strap.

segler said..
What matters in the end is where the front wing is located relative to the foot positions (or footstraps if you use those).

Some foils, like my AFS-2 rake the masts, either forward or aft. My AFS-2 rakes forward. Most masts are 90 deg with no rake.

However, you should still try to determine where the front wing is located when it is all assembled. If you have a dual track mounting, it is easy to move the whole foil fore and aft to adjust. If you have a DT box, you have to adjust footstraps and/or sail mast base and/or fuse length or mount to adjust.

See this old youtube I made a few years ago. It was for a forward-raked mast with DT box.

Well thats interesting. I have an AFS W85 mast and F1080 v2 foil setup on an AHD Compact 83 foilboard.
Front wing is roughly mid way between the straps, although I havent measured it.
The distance from the front foil bolt to usual mast base position is 112cm, +/- 1cm depending upon sail used and wind speed. So the same as yours within a gnats whisker. I use 6.5/7.5/8.5m Ezzy Lions.
I reckon if the front wing was further back and couldnt move the straps then you would need to bring the mastbase a lot further back to compensate.
I dont have a lot of foiling experience yet, but others around me do. They have their front wing lining up between the straps as well.
The only person who doesnt has an AHD Topac fin board with DT foilbox, and a Slingshot foil (and DT adaptor), of the type normally used with dual US boxes where you can move the foil forward. His front wing is a lot nearer the rear straps than the front, and he struggled to get going on that setup.

Sam Ross is now the UK head coach for the Olympic team.

I've just noticed in that AlpineFoil board video the mast track is centred at 125cm. Is that quite far back for a freerace setup?

They also have the square hole to put the UJ in the middle of the track so you cant use it there! 23"29.

Here is an updated image. The board was originally developed in collaboration with F4 foils so I guess they are still perfectly compatible.
Green is my Alpinefoil A1 Carbon front wing midpoint position.
Blue is the current F4 Race foil wing midpoint position. (measuring from the images available on the website)



From what I know and probably worth noting is that the center of lift is actually closer to the first third of the foil chord from the leading edge. I'm not sure how the stabilizer affects the position of the center of lift.
Also to draw on airplane dynamics... In general a stable airplane should have the Center of Gravity in front of the center of lift. Knowing that it should follow that the foil center of lift should in fact be slightly behind the midpoint between the foot-straps. But then again the board has a lot of weight in front and there is also the sail weight and lift to account for... to much to know intuitively what that does to the Center of Gravity.

aeroegnr said..
I tried to scale as exactly as possible based off of board lengths to compare to the other boards I have foiled recently by aligning on the tuttle screws.

The JP is very similar tuttle to track positions to the Blast. The Blast felt good with the Slingshot 76 in B position and I also rode it with the Starboard 105+ fuse and the 725 wing. Looks like the JP has a mast track further aft which definitely helps you not need to keep the base all the way back in the track. I just didn't like the feel of where the rear straps were, nor the tail width on the Blast when jibing.

It has less forward of a mast track as the IQFoil board even though they have the same overall length and similar width (95cm IQ vs. 89 JP). It was designed with either the 115+ or 95+ (I've also used the 105+). When I ride the 105+ I take the mast track about 1cm back, could probably go a little bit more. I'm not sure about the comparison with your foil but it looks like the track is in the right place for that. The IQFoil board has to work with a fin in fin mode (which has the mast position recommended 2cm more forward if I recall correctly).

I've only used the FoilX with the slingshot 76 in B, but it's clear how close to the footstraps the track is vs. yours, however it is more geared towards freeride vs. race,

Thank you for the great comparison!
It looks like from the images you provided that the lower end foil boards tend to have the mast track further back to accommodate the free ride or beginner foils. Also most race foils have long fuselages and this would make sense if the Center of lift should be closer to the midpoint between the foot-straps.

aeroegnr said..
Also as a point of comparison is the back of the 725 starboard front to the opening for the foil mast, which is 22cm. Seems the Alpine is quite far back?

Edit: sorry this is the 105+ fuse. The 115+ is even further forward.

Looks like with the old wing that came with the A1 Carbon when I bought it, this measurement is somewhere around 16,3 cm.
The measurements in the first post are with the newer wing: ULW1200.

aeroegnr said..

Mushin said..

aeroegnr said..
Also as a point of comparison is the back of the 725 starboard front to the opening for the foil mast, which is 22cm. Seems the Alpine is quite far back?

Edit: sorry this is the 105+ fuse. The 115+ is even further forward.

Looks like with the old wing that came with the A1 Carbon when I bought it, this measurement is somewhere around 16,3 cm.
The measurements in the first post are with the newer wing: ULW1200.

Is it possible to switch fuses? Are you using the new wing with the old fuse? I have no clue about their foils at all but it seems like a longer fuse length in front would really help you all around for performance.

Yes I think their fuselages are 100% compatible with all the wings but I will check with them to make sure.
Yes, the ULW1200 is compatible with my old fuse (checked when buying with Damien) he said it is so good it is basically a complete replacement for the old one. I got going much easier with the ULW1200 and the race stabilizer compared to the old 900cm2 wing with the default stab.

Sandman1221 said..
Mushin You mentioned above how you felt you were planing but could not get up on the foil. With my AFS W95 foil when I had that problem it was solved by putting a 0.5 mm AFS shim under the front of the stabilizer, then the foil came up easily! I think I saw a shim set on the Alpinefoil website. I now always run the AFS foil with the 1 shim on the stabilizer, with any of the 3 wings I have (F1080 F770 S670) and in any wind condition from 8-30 knots.

I mentioned the use of +0.7 shim in my first post, that made it easier also in lower wind i tried the +1.5 shim. But I think that a need for a shim in a broad range of wind conditions like that could really be a sign of the foil not being in balance. Maybe other experienced riders can comment on that.

Mushin said..

Sandman1221 said..
Mushin You mentioned above how you felt you were planing but could not get up on the foil. With my AFS W95 foil when I had that problem it was solved by putting a 0.5 mm AFS shim under the front of the stabilizer, then the foil came up easily! I think I saw a shim set on the Alpinefoil website. I now always run the AFS foil with the 1 shim on the stabilizer, with any of the 3 wings I have (F1080 F770 S670) and in any wind condition from 8-30 knots.

I mentioned the use of +0.7 shim in my first post, that made it easier also in lower wind i tried the +1.5 shim. But I think that a need for a shim in a broad range of wind conditions like that could really be a sign of the foil not being in balance. Maybe other experienced riders can comment on that.

I think the way AFS made the foil was for the stabilizer to be neutral, so that you could shim it based on the board maybe?, foil is perfectly balanced on my board with the 1 shim, they made the shims for a reason!

Sandman1221 said..

Mushin said..

Sandman1221 said..
Mushin You mentioned above how you felt you were planing but could not get up on the foil. With my AFS W95 foil when I had that problem it was solved by putting a 0.5 mm AFS shim under the front of the stabilizer, then the foil came up easily! I think I saw a shim set on the Alpinefoil website. I now always run the AFS foil with the 1 shim on the stabilizer, with any of the 3 wings I have (F1080 F770 S670) and in any wind condition from 8-30 knots.

I mentioned the use of +0.7 shim in my first post, that made it easier also in lower wind i tried the +1.5 shim. But I think that a need for a shim in a broad range of wind conditions like that could really be a sign of the foil not being in balance. Maybe other experienced riders can comment on that.

I think the way AFS made the foil was for the stabilizer to be neutral, so that you could shim it based on the board maybe?, foil is perfectly balanced on my board with the 1 shim, they made the shims for a reason!

I understand it in the way an airplane works, elevators are used to make the plane fly with lower speed or even higher speed. When flying in a straight line at optimum speed they are set to neutral. There is also a control aspect to the elevators which is not relevant for foils. So the shims can be used to change the angle of attack to make the foil fly with lower speed. However changing the angle of attack from default neutral decreases the overall efficiency mainly by causing more drag. Also I think it might affect stability of the foil in a bad way at speeds the shims were not intended to be used. So in short elevators are replaced by the stabilizer shim and flaps are replaced by the main wing shim on the foil.

If the foil is to far back adding negative lift makes it counteract the imbalance of having the Center of Gravity to far forward from the Center of lift. But it comes at a cost of increased drag and possibly worse stability. The user might have the feeling of better stability because it's not necessary to constantly press on the back leg... but that might be misleading.

It is however possible that some foils might be deliberately designed this way but I think it would be mentioned explicitly in the user manual or something.

I am not actually an expert for foils or an airplane engineer so if someone is... your opinion is welcome!