Hi
Regarding getting max stability I've seen two options:
- Longer distance from foil to sail
- Very small distance from foil to sail to reduce influence of sail pressure. More similar to winging

I guess in both cases longer fuselages give more stability, or in the second case is not so important?

I mean stability in vertical plane, not in horizontal one.

Cheers

Foil shape, tail shape/size, fuselage length.

All much more important than the spacing between masts. Also getting the foot pressure biased towards the front.

Hello
I recover this topic because I thought it would be interesting for many people. I will describe it in a different way.

Could you use the same foil in terms of fuselage, wings, etc in so different boards such as a Goya Airbolt and a SS wizzard of the same volume, taking into account the distance from foil mast to sail base are completely different? I guess no. What would be the more stable configuration, bigger distance or small distance? Which configuration would be more suitable in each case?

For example, I guess in the Goya you would need an smaller front wing to fly as early as with the SS, because the wing is much more forward.

Thanks.

my feeling is running the sail further back in the track will make it more stable on pitch

Vertical board height is adjusted using front and rear foot pressure, the more balanced the rider is the easier it is to adjust height, and maintain a given height off the water. If the board has a DT foil box, the only way to adjust the balance of the kit is to move the sail mast base. But if you have tracks, or use a jack plate, you can also move the position of the foil.

The goal is to feel like you are straddling the pivot point of a see-saw, with your front and rear foot an equal distance from the pivot point.

Certainly longer fuse.

You can use the same foil on different boards wiith different foiil to sail distances but you will need to adjust where you stand so that the thing flys (leaving shims out of it for now)

For example if you increase your the distance the sail is from the foil mast the more leverage the MFP is putting down on the foil so you need to reduce the torque from your body weight be standing further back

As you move the mast foot back you increase the sensitivity of the system to shifts in your body weight. Does that make it less stable vertically? I would argue yes, espescially if you haven't developed enought skill to handle the added control.

Select to expand quote

thedoor said..
Certainly longer fuse.

You can use the same foil on different boards wiith different foiil to sail distances but you will need to adjust where you stand so that the thing flys (leaving shims out of it for now)

For example if you increase your the distance the sail is from the foil mast the more leverage the MFP is putting down on the foil so you need to reduce the torque from your body weight be standing further back

As you move the mast foot back you increase the sensitivity of the system to shifts in your body weight. Does that make it less stable vertically? I would argue yes, espescially if you haven't developed enought skill to handle the added control.

Yep with the same boards there's a huge difference in feel and stability with 95+, 105+, and 115+ fuses with the same front and rear wings. But the shorter fuses need more shims to be balanced without too much back foot pressure.

At first it was hard to distinguish between sail and foil stability with my setups, but as time goes on the more I feel the difference, especially on the foilx that has a very short mast track to foil mast distance. When the sail is unstable due to poor rigging or being overpowered I can usually still ride the foil fine unless I'm trying to push for speed. On race kit there's a big difference in stability upwind by adjusting outhaul pressure. Especially with the 9.0 hgo in 14+ knots, you need to pull lots of outhaul or it gets too much lift too quickly for mortals like me to react. And downwind it feels different when you dump it for more belly in the sail.

Select to expand quote

Sandman1221 said..
If the board has a DT foil box, the only way to adjust the balance of the kit is to move the sail mast base.

Not all. It is the easiest and quickest way for most people, though. You should add
a) boom height
b) foot strap location
c) stab shimming
d) foil fore/aft angle ie shimming foil at foilbox
e) sail, whether draft forward or aft
f) board heel dynamically altering balance of kit by reducing foil lift. e.g. faster foilers use this to decrease amount of lift at higher speeds.


The greater the distance between the center of gravity/pressure to the center of lift, the more stable things should be. "The longitudinal static stability of an aircraft depends on the location of its center of gravity relative to the neutral point. As the center of gravity moves increasingly forward, the pitching moment arm is increased, increasing stability.[5][4] The distance between the center of gravity and the neutral point is defined as "static margin". ...The greater the static margin, the more stable the aircraft will be." - en.wikipedia.org/wiki/Longitudinal_stability#Static_stability

This is also why longer fuses are more stable: longer moment arms.

However, as mentioned by some above, moving the sail much closer to the mast reduces the effect of having power in the sail altering ride height. It doesn't so much alter the physics of the balance but reduces how much sail pressure influences ride height. By similar token, one principal reason for shorter boom foil sails is the same - longer boomed sails especially on the big side are less ride stable.

Select to expand quote

aeroegnr said..

thedoor said..
Certainly longer fuse.

You can use the same foil on different boards wiith different foiil to sail distances but you will need to adjust where you stand so that the thing flys (leaving shims out of it for now)

For example if you increase your the distance the sail is from the foil mast the more leverage the MFP is putting down on the foil so you need to reduce the torque from your body weight be standing further back

As you move the mast foot back you increase the sensitivity of the system to shifts in your body weight. Does that make it less stable vertically? I would argue yes, espescially if you haven't developed enought skill to handle the added control.

Yep with the same boards there's a huge difference in feel and stability with 95+, 105+, and 115+ fuses with the same front and rear wings. But the shorter fuses need more shims to be balanced without too much back foot pressure.

At first it was hard to distinguish between sail and foil stability with my setups, but as time goes on the more I feel the difference, especially on the foilx that has a very short mast track to foil mast distance. When the sail is unstable due to poor rigging or being overpowered I can usually still ride the foil fine unless I'm trying to push for speed. On race kit there's a big difference in stability upwind by adjusting outhaul pressure. Especially with the 9.0 hgo in 14+ knots, you need to pull lots of outhaul or it gets too much lift too quickly for mortals like me to react. And downwind it feels different when you dump it for more belly in the sail.

the big advantages of having the closer distance seems to be you can control an over lifting foil easier with weight shifts instead of stepping back foot forwards, and poor sail movements have less impact on ride height.

re the diff fuses for your race kit. My understanding is that the long ones generate so much lift that you basically cannot safely reach and mostly go upwind and downwind?

Select to expand quote

thedoor said..

aeroegnr said..

thedoor said..
Certainly longer fuse.

You can use the same foil on different boards wiith different foiil to sail distances but you will need to adjust where you stand so that the thing flys (leaving shims out of it for now)

For example if you increase your the distance the sail is from the foil mast the more leverage the MFP is putting down on the foil so you need to reduce the torque from your body weight be standing further back

As you move the mast foot back you increase the sensitivity of the system to shifts in your body weight. Does that make it less stable vertically? I would argue yes, espescially if you haven't developed enought skill to handle the added control.

Yep with the same boards there's a huge difference in feel and stability with 95+, 105+, and 115+ fuses with the same front and rear wings. But the shorter fuses need more shims to be balanced without too much back foot pressure.

At first it was hard to distinguish between sail and foil stability with my setups, but as time goes on the more I feel the difference, especially on the foilx that has a very short mast track to foil mast distance. When the sail is unstable due to poor rigging or being overpowered I can usually still ride the foil fine unless I'm trying to push for speed. On race kit there's a big difference in stability upwind by adjusting outhaul pressure. Especially with the 9.0 hgo in 14+ knots, you need to pull lots of outhaul or it gets too much lift too quickly for mortals like me to react. And downwind it feels different when you dump it for more belly in the sail.

the big advantages of having the closer distance seems to be you can control an over lifting foil easier with weight shifts instead of stepping back foot forwards, and poor sail movements have less impact on ride height.

re the diff fuses for your race kit. My understanding is that the long ones generate so much lift that you basically cannot safely reach and mostly go upwind and downwind?

Yeah that's what compact geometry on the foilx vs other boards feels like to me. I do move my feet around some if I don't have the back straps on but it's not like I do on race gear. It's mild enough that I can ride it in the straps unless massively overpowered and want more margin.

The 115+ yes, I have trouble reaching (but I'm not sure what that says vs what my skill level is) above a certain wind speed. In really light stuff I can. It also helps massively when powered up to drop the boom because it puts more mast base pressure down.

The 105+ is super stable compared to the 95+, but the black 115/115 classic is even more stable without the far forward lift and people love those for fast reach/downwind (so I've been told).

Select to expand quote

thedoor said..
For example if you increase your the distance the sail is from the foil mast the more leverage the MFP is putting down on the foil so you need to reduce the torque from your body weight be standing further back
As you move the mast foot back you increase the sensitivity of the system to shifts in your body weight. Does that make it less stable vertically? I would argue yes, espescially if you haven't developed enought skill to handle the added control.

It doesn't seem sail mast-base pressure has as much effect as I'd previously thought (at least with freeride sails).

Experimented a couple of months ago offsetting the mast-base closer to the rail, to see if I could angle the board/foil more into the wind when going upwind.
Before testing we thought it'd be super-tricky to gybe.

Tested on a marginal 10-14 knots with 5.9m Simmer Enduro, properly powered up a few times on both tacks.
Turns out it was simple to gybe, hardly noticed any change.
Made no difference to the amount I could angle the board into the wind.
Easier to get going with the mast base on the leeward side.
Fun carving downwind as the arcs of the turns varied (tighter with the mast-base on windward side).

Windsurfing physics has always been a large part mystery and I reckon windfoiling even more so

Select to expand quote

azymuth said..

thedoor said..
For example if you increase your the distance the sail is from the foil mast the more leverage the MFP is putting down on the foil so you need to reduce the torque from your body weight be standing further back
As you move the mast foot back you increase the sensitivity of the system to shifts in your body weight. Does that make it less stable vertically? I would argue yes, espescially if you haven't developed enought skill to handle the added control.

It doesn't seem sail mast-base pressure has as much effect as I'd previously thought (at least with freeride sails).

Experimented a couple of months ago offsetting the mast-base closer to the rail, to see if I could angle the board/foil more into the wind when going upwind.
Before testing we thought it'd be super-tricky to gybe.

Tested on a marginal 10-14 knots with 5.9m Simmer Enduro, properly powered up a few times on both tacks.
Turns out it was simple to gybe, hardly noticed any change.
Made no difference to the amount I could angle the board into the wind.
Easier to get going with the mast base on the leeward side.
Fun carving downwind as the arcs of the turns varied (tighter with the mast-base on windward side).

Windsurfing physics has always been a large part mystery and I reckon windfoiling even more so

Hah now that's a creative experiment!

Select to expand quote

azymuth said..

thedoor said..
For example if you increase your the distance the sail is from the foil mast the more leverage the MFP is putting down on the foil so you need to reduce the torque from your body weight be standing further back
As you move the mast foot back you increase the sensitivity of the system to shifts in your body weight. Does that make it less stable vertically? I would argue yes, espescially if you haven't developed enought skill to handle the added control.

It doesn't seem sail mast-base pressure has as much effect as I'd previously thought (at least with freeride sails).

Experimented a couple of months ago offsetting the mast-base closer to the rail, to see if I could angle the board/foil more into the wind when going upwind.
Before testing we thought it'd be super-tricky to gybe.

Tested on a marginal 10-14 knots with 5.9m Simmer Enduro, properly powered up a few times on both tacks.
Turns out it was simple to gybe, hardly noticed any change.
Made no difference to the amount I could angle the board into the wind.
Easier to get going with the mast base on the leeward side.
Fun carving downwind as the arcs of the turns varied (tighter with the mast-base on windward side).

Windsurfing physics has always been a large part mystery and I reckon windfoiling even more so

anyone else wondering what other crazyness JJ hasn't shared with us?

Select to expand quote

azymuth said..

thedoor said..
For example if you increase your the distance the sail is from the foil mast the more leverage the MFP is putting down on the foil so you need to reduce the torque from your body weight be standing further back
As you move the mast foot back you increase the sensitivity of the system to shifts in your body weight. Does that make it less stable vertically? I would argue yes, espescially if you haven't developed enought skill to handle the added control.

It doesn't seem sail mast-base pressure has as much effect as I'd previously thought (at least with freeride sails).

Experimented a couple of months ago offsetting the mast-base closer to the rail, to see if I could angle the board/foil more into the wind when going upwind.
Before testing we thought it'd be super-tricky to gybe.

Tested on a marginal 10-14 knots with 5.9m Simmer Enduro, properly powered up a few times on both tacks.
Turns out it was simple to gybe, hardly noticed any change.
Made no difference to the amount I could angle the board into the wind.
Easier to get going with the mast base on the leeward side.
Fun carving downwind as the arcs of the turns varied (tighter with the mast-base on windward side).

Windsurfing physics has always been a large part mystery and I reckon windfoiling even more so

What made you think of doing that?! it is really far out of the box!, figuratively speaking.

Select to expand quote

thedoor said..

azymuth said..

thedoor said..
For example if you increase your the distance the sail is from the foil mast the more leverage the MFP is putting down on the foil so you need to reduce the torque from your body weight be standing further back
As you move the mast foot back you increase the sensitivity of the system to shifts in your body weight. Does that make it less stable vertically? I would argue yes, espescially if you haven't developed enought skill to handle the added control.

It doesn't seem sail mast-base pressure has as much effect as I'd previously thought (at least with freeride sails).

Experimented a couple of months ago offsetting the mast-base closer to the rail, to see if I could angle the board/foil more into the wind when going upwind.
Before testing we thought it'd be super-tricky to gybe.

Tested on a marginal 10-14 knots with 5.9m Simmer Enduro, properly powered up a few times on both tacks.
Turns out it was simple to gybe, hardly noticed any change.
Made no difference to the amount I could angle the board into the wind.
Easier to get going with the mast base on the leeward side.
Fun carving downwind as the arcs of the turns varied (tighter with the mast-base on windward side).

Windsurfing physics has always been a large part mystery and I reckon windfoiling even more so

anyone else wondering what other crazyness JJ hasn't shared with us?

I'm willing to bet he has more up his sleeve. It is the Wizard, after all...

Select to expand quote

azymuth said..

thedoor said..
For example if you increase your the distance the sail is from the foil mast the more leverage the MFP is putting down on the foil so you need to reduce the torque from your body weight be standing further back
As you move the mast foot back you increase the sensitivity of the system to shifts in your body weight. Does that make it less stable vertically? I would argue yes, espescially if you haven't developed enought skill to handle the added control.

It doesn't seem sail mast-base pressure has as much effect as I'd previously thought (at least with freeride sails).

Experimented a couple of months ago offsetting the mast-base closer to the rail, to see if I could angle the board/foil more into the wind when going upwind.
Before testing we thought it'd be super-tricky to gybe.

Tested on a marginal 10-14 knots with 5.9m Simmer Enduro, properly powered up a few times on both tacks.
Turns out it was simple to gybe, hardly noticed any change.
Made no difference to the amount I could angle the board into the wind.
Easier to get going with the mast base on the leeward side.
Fun carving downwind as the arcs of the turns varied (tighter with the mast-base on windward side).

Windsurfing physics has always been a large part mystery and I reckon windfoiling even more so

I know the course racing guys tried this a few years ago. Apparently was an improvement up wind. More leverage, like having a wider board. I've always liked the 115 plus fuse for slalom up to 12 / 18 knots and 725. Front wing forward and less rear wing angle. Felt more stable than the 105 plus.

I think the main thing for stability is TOW. Since foiling introduced the vertical for the first time, we all had to learn how to manage the vertical. It took a while.

Select to expand quote

DarrylG said..

azymuth said..

thedoor said..
For example if you increase your the distance the sail is from the foil mast the more leverage the MFP is putting down on the foil so you need to reduce the torque from your body weight be standing further back
As you move the mast foot back you increase the sensitivity of the system to shifts in your body weight. Does that make it less stable vertically? I would argue yes, espescially if you haven't developed enought skill to handle the added control.

It doesn't seem sail mast-base pressure has as much effect as I'd previously thought (at least with freeride sails).

Experimented a couple of months ago offsetting the mast-base closer to the rail, to see if I could angle the board/foil more into the wind when going upwind.
Before testing we thought it'd be super-tricky to gybe.

Tested on a marginal 10-14 knots with 5.9m Simmer Enduro, properly powered up a few times on both tacks.
Turns out it was simple to gybe, hardly noticed any change.
Made no difference to the amount I could angle the board into the wind.
Easier to get going with the mast base on the leeward side.
Fun carving downwind as the arcs of the turns varied (tighter with the mast-base on windward side).

Windsurfing physics has always been a large part mystery and I reckon windfoiling even more so

I know the course racing guys tried this a few years ago. Apparently was an improvement up wind. More leverage, like having a wider board. I've always liked the 115 plus fuse for slalom up to 12 / 18 knots and 725. Front wing forward and less rear wing angle. Felt more stable than the 105 plus.

You're reminding me that I need to try smaller than the 900 now that there's some wind. For the 12/18 are you on a 9.0 or smaller?