I have heard that cammed sails produced more down force on the board. Is that just cause they are more powerful? Or for a given amount of power is the vector from cammed sails thru the mast foot more vertical than non cammed sails.

Background: today I was foiling (w999/s450) with a 5.4 single cam sail, which I have been using more since I "fixed" the rotation issue. Generally when I foil I keep all my geometry (universal, foil mast, straps etc) the same. Today and prior I noticed with the 5.4 single cam I needed to keep my feet slightly further back on the board to offset the extra weight or mast foot pressure (MFP) of the single cam.

I switched down to my 4.7 wave sail (same geometry) just to experience the difference and I found I was much better off with the wave sail. So I started to wonder about the ratio of sail power to MFP. Although I would expect a 5.4 single cam to be more powerful than the 4.7 wave sail I was thinking this power comes at the expense of much more MFP, which impacts my ability to foil with my normal geometry.

If the vector angle varies for different styles of sails, then my hypothesis is that for freeride foiling a higher power to MFP ratio is more important than max power.

Or is there another explanation for my preference for the 4.7 wave sail over the 5.4 single cam in similar underpowered conditions?

I'm not sure of this, but it may not just be Mast foot pressure in a vertical direction.
It could be more forward at the top of the sail, this has rotational leverage, pushing the nose down, you have to shift your weight back to counter balance it.

More likely that it is due to free ride and race sails having less bottom end.
well known to me when trying to have a wide range of use on a FSW board. All wave sails up to 5.7 and then a 7m free ride sail. With almost no benefit. I was far better going with a 6.5 power wave/ crossover type thing

Of course this will depend on what sail that cammed one is but most are designed to be used top end


Then - is it just heavier? So mayybeee less power than expected and a heavier rig so you need a smidge of backfoot

Your mast foot position would change as you sail change size. I start in the middle with 6.2 and forward as sails are bigger and back for smaller. I like to have similar feet pressure when I go out to keep me comfy. Bigger sail have more lift so move then fwd to counteract and small sails have less lift so move them back. Same as on the fin. But there's lots to consider re foot position and front wing size and foot strap placement style of sail and stab angle. Im on 3cam sails and getting used to a 650/190 combo with 7.6-5.2 sails. Flying most gybes speed is getting up from last season and going out over powered too often. I've just set someone up with foil kit and given instruction to start with foot in middle of track for his largest sail. Only a 5.6. And then work from there. More lift, move it back & less fwd. he will try to slap with kit and keep it on the water for about 20min then encourage lift and straight back down again then progress to short flights and regular landings with flights getting longer after 40min and should have 20-50m controlled flights within the hr. If he keeps his head, I said no crashes in the first hr cos the board shouldn't get that far out of the water.

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thedoor said..
I have heard that cammed sails produced more down force on the board. Is that just cause they are more powerful? Or for a given amount of power is the vector from cammed sails thru the mast foot more vertical than non cammed sails.

Background: today I was foiling (w999/s450) with a 5.4 single cam sail, which I have been using more since I "fixed" the rotation issue. Generally when I foil I keep all my geometry (universal, foil mast, straps etc) the same. Today and prior I noticed with the 5.4 single cam I needed to keep my feet slightly further back on the board to offset the extra weight or mast foot pressure (MFP) of the single cam.

I switched down to my 4.7 wave sail (same geometry) just to experience the difference and I found I was much better off with the wave sail. So I started to wonder about the ratio of sail power to MFP. Although I would expect a 5.4 single cam to be more powerful than the 4.7 wave sail I was thinking this power comes at the expense of much more MFP, which impacts my ability to foil with my normal geometry.

If the vector angle varies for different styles of sails, then my hypothesis is that for freeride foiling a higher power to MFP ratio is more important than max power.

Or is there another explanation for my preference for the 4.7 wave sail over the 5.4 single cam in similar underpowered conditions?

Do you ever change mast foot position when changing sails?
Cam sails should have more power and stability. C of E is more stable, high low fwd or central. Higher boom affects sail lift too.

Fwd mast foot position is telling the board that you want the nose down, standing behind back strap is telling the board you want the nose up there's a contradiction.

No real need to move mast foot with my wave sails 3.2-5.3 which is nice. I have heard that people on more racier gear do move there mast foot around as conditions change, but that is quite different to the gear I ride

These technical questions are always interesting - but we also find that many people talk at cross purposes, as in this thread.
Let's separate the three specific issues here:

1) Mast foot pressure is a term we use when teaching windsurfing, and it's really about helping the sailor get the board level, so as not to sink the tail. The board planes earlier, if it starts out flat, and it's mast foot pressure that usually achieves that. You get mast foot pressure by leaning forwards on the board, and by weighting the boom downwards - and some people find they get more mast foot pressure if they raise the boom a touch on the mast. The real discussion about mast foot pressure is also to make you, the sailor, engage rig power so as to drive the board forwards. And, for the beginner, it's applying basic mast foot pressure that also stops the board slewing into the wind, when you first get going.

2) Rig power is more about sail size first, and then it's about how you rig that chosen sail. Easing the outhaul puts more belly in the sail, and that setting can give you more power for acceleration. If instead you leave the downhaul off a touch then the leach tightens, allowing the sail to pull much powerfully but from higher up. Racing sailors claim that the correct sail setting then controls board trim, perhaps with a tighter leech holding the nose down - with better leverage from the upper sail area. The windy weather setting is where you apply more downhaul, and that should release the excess power from the head of the sail better, with the sail drive then coming from lower down the rig.

3) People have mentioned mast foot position, but that controls power in a different way - and is more about board control. Shifting the mast foot forwards takes the rig drive point away from the lift of the fin, so you can then control railing more. Shifting the mast foot forwards also increases mast rake, and that alone tends to make the sailor weight the board tail more, something useful again if you need more control or if the board is 'tail walking'.. But for more power and for earlier planing, you might do the reverse - namely shifting the mast foot back in the track so as to bring the rig drive nearer the fin. Bringing the mast foot back also sets the mast more upright, and any board will be more manoeuvrable in that setting if the sailor adopts an upright stance to match.

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thedoor said..
I have heard that cammed sails produced more down force on the board. Is that just cause they are more powerful? Or for a given amount of power is the vector from cammed sails thru the mast foot more vertical than non cammed sails.


Or is there another explanation for my preference for the 4.7 wave sail over the 5.4 single cam in similar underpowered conditions?

How do you compare power between sail types? Race kit is designed to be used in a larger size for the same wind strength so they are faster. So you cant compare a 6m cammed race to a 6m wave.

Like most forms of windsurfing including the foiling you do, match the sail to the board. For fin sailing, wave sail for wave boards, slalom sail to slalom boards, freeride sails to freeride sails and you will have a better time because the kit feels balanced.
For foiling, and I assume you have a low aspect foil from what you have written saying you use wave sails, then putting a cammed freerace sail doesnt make sense to me.

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PhilUK said.How do you compare power between sail types? Race kit is designed to be used in a larger size for the same wind strength so they are faster. So you cant compare a 6m cammed race to a 6m wave.

^^^ yes that

if you go up one size at a time in wave sails, then one size in a race sail you will be sadly disappointed
its a myth that cammed is more powerful

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Basher said..
These technical questions are always interesting - but we also find that many people talk at cross purposes, as in this thread.
Let's separate the three specific issues here:

1) Mast foot pressure is a term we use when teaching windsurfing, and it's really about helping the sailor get the board level, so as not to sink the tail. The board planes earlier, if it starts out flat, and it's mast foot pressure that usually achieves that. You get mast foot pressure by leaning forwards on the board, and by weighting the boom downwards - and some people find they get more mast foot pressure if they raise the boom a touch on the mast. The real discussion about mast foot pressure is also to make you, the sailor, engage rig power so as to drive the board forwards. And, for the beginner, it's applying basic mast foot pressure that also stops the board slewing into the wind, when you first get going.

2) Rig power is more about sail size first, and then it's about how you rig that chosen sail. Easing the outhaul puts more belly in the sail, and that setting can give you more power for acceleration. If instead you leave the downhaul off a touch then the leach tightens, allowing the sail to pull much powerfully but from higher up. Racing sailors claim that the correct sail setting then controls board trim, perhaps with a tighter leech holding the nose down - with better leverage from the upper sail area. The windy weather setting is where you apply more downhaul, and that should release the excess power from the head of the sail better, with the sail drive then coming from lower down the rig.

3) People have mentioned mast foot position, but that controls power in a different way - and is more about board control. Shifting the mast foot forwards takes the rig drive point away from the lift of the fin, so you can then control railing more. Shifting the mast foot forwards also increases mast rake, and that alone tends to make the sailor weight the board tail more, something useful again if you need more control or if the board is 'tail walking'.. But for more power and for earlier planing, you might do the reverse - namely shifting the mast foot back in the track so as to bring the rig drive nearer the fin. Bringing the mast foot back also sets the mast more upright, and any board will be more manoeuvrable in that setting if the sailor adopts an upright stance to match.

A good wrap up of concepts

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Mark _australia said..

Basher said..
These technical questions are always interesting - but we also find that many people talk at cross purposes, as in this thread.
Let's separate the three specific issues here:

1) Mast foot pressure is a term we use when teaching windsurfing, and it's really about helping the sailor get the board level, so as not to sink the tail. The board planes earlier, if it starts out flat, and it's mast foot pressure that usually achieves that. You get mast foot pressure by leaning forwards on the board, and by weighting the boom downwards - and some people find they get more mast foot pressure if they raise the boom a touch on the mast. The real discussion about mast foot pressure is also to make you, the sailor, engage rig power so as to drive the board forwards. And, for the beginner, it's applying basic mast foot pressure that also stops the board slewing into the wind, when you first get going.

2) Rig power is more about sail size first, and then it's about how you rig that chosen sail. Easing the outhaul puts more belly in the sail, and that setting can give you more power for acceleration. If instead you leave the downhaul off a touch then the leach tightens, allowing the sail to pull much powerfully but from higher up. Racing sailors claim that the correct sail setting then controls board trim, perhaps with a tighter leech holding the nose down - with better leverage from the upper sail area. The windy weather setting is where you apply more downhaul, and that should release the excess power from the head of the sail better, with the sail drive then coming from lower down the rig.

3) People have mentioned mast foot position, but that controls power in a different way - and is more about board control. Shifting the mast foot forwards takes the rig drive point away from the lift of the fin, so you can then control railing more. Shifting the mast foot forwards also increases mast rake, and that alone tends to make the sailor weight the board tail more, something useful again if you need more control or if the board is 'tail walking'.. But for more power and for earlier planing, you might do the reverse - namely shifting the mast foot back in the track so as to bring the rig drive nearer the fin. Bringing the mast foot back also sets the mast more upright, and any board will be more manoeuvrable in that setting if the sailor adopts an upright stance to match.

A good wrap up of concepts

Not much to do with foiling specifics though.
As Decrepit said, "It [MFP] could be more forward at the top of the sail, this has rotational leverage, pushing the nose down" is totally different to MFP a windsurfing beginner leans to keep the board flat (and I think that idea is overstated).

If you look at the differences in setup of a slalom board and wave board regarding mastfoot placement, for a slalom board the distance to that a lot more than the distance on a wave board. So I would expect on a foil board that would be a similar thing using fin sails, but what about foil cammed sails? I dont know, as they are designed for foiling and I havent used them.

In my experience, letting the outhaul off to get more belly and more power is fine on a low aspect foil, but not on higher aspect foils. When I started I used Ezzy 2 cam Lion with less downhaul and outhaul than normal, and that gave a lot of belly in the sail and more power. But soon I realised (and was told) that for better speed flatter was better. I now use way more outhaul on the foil than for fin. Too much belly/power makes it unstable in gusts and stronger winds. When I started there was 1 lad was on low aspect Severne foil and bagged out 5.8m wave sail, and another oh high aspect slalom foil and foil cammed sails and got told different advice. As I use a more higher aspect freeride and Lions for me its flatter settings which work best. More 'power' didnt lead to faster speeds and better acceleration, but more crashes.

I guess the reason I am comparing them is that they are close in size and the fact that it is only one cam, I don't think it is intended to replace a race sail. But points made might be valid: if the single cam in the 5.4 was meaningful enough to alter downforce like a race sail then perhaps it is too small of a size difference to be comparable in power to the 4.7 wave sail

Here is a video of the single cam

I do the same as phil for low aspect foils versus fin on the same sail: 1-2cm extra outhaul for foil

Sail shape and how it lifts/pushes can be very different due to various reasons.

First off it depends on where the designer has put the shape, it can also change due to batten angles, luff curve, seam shape etc, there are loads of variables.

Sometimes it can depend on who is testing the sails and with what board/fin set up too.

Usually specific slalom sails pin the board down and have good forward drive where as freestyle sails / wave sails lift the sailor up.

As PhilUK pointed out, I completely ignored the fact that this question was partly about foiling.
That's because I don't do windfoiling or wingfoiling, and because I wanted to keep my technical answer short.

But the key to all foiling thinking is that 1) You are probably doing foiling in lighter winds, and 2)The horizontal front foil itself gives an upward lift which means your sailing stance over the board must change to counteract that upward lift.
3) Those two first points also mean a foiling sail works best if it generates a downward force as well as the forward-drive - so we are on topic here.

Starting with point 1), The typical sail use in lighter winds means the sail twist needed for foiling is different from that used for conventional slalom windsurfing. This is because the extra board speed in light wind gives different sheeting angles where you stay sheeted in more, even when heading broad off the wind. The sail of course still sets to the apparent wind, which made up of board speed and direction plus the true wind of the day. It's just that the proportions of the two have changed, with board speed making 'created wind'a bigger component of apparent wind.
2) All sailing craft - including foiling boards - will have specific needs when operating in lighter winds, and the optimum sail plan for foiling is a high aspect sail and a tighter leach. Where sail manufacturers make a foiling-dedicated sail, you should find that has a longer mast and maybe a shorter boom. But the fullness cut in the top of the sail is also greater. Those sail design changes not only work better with the apparent wind but they increase the downforce over the foil.
3) We can of course use conventional sails for foiling - even the wave sails we already have. But, as said earlier in this thread, the way you adapt them for foiling is to let the downhaul off a little, to tighten the upper leach, and to create more downforce from the head of the sail.
4) Cambered sails can work well for foiling in that they create a veery stable sail set on a longer mast, plus the twin luff acts as an aerodynamic 'wing mast' to reduce drag . The induced sail fullness will also help at low speeds and for acceleration. But a flattish sail is also fast for top speed, and so rotational sails can work really well for lighter wind foiling fun, plus rotational sails have a weight advantage.