Have been trying to better understand sail trim and it's dynamics and have widely researched the applications of downhaul and outhaul on a sail's shape and I am finding some conflicting information in various windsurfing articles and videos on the subject. Have also gone to Australian Yachting lecture videos and asked local experienced sailors their opinion on the subject to try to understand. Have I got it right?
*more DOWNHAUL = draft forward
*more OUTHAUL = draft forward

Hi Mickey, yes that's correct.

Some describe it as draft forward, others as less back hand pressure. But both mean the same thing.

what does "draft forward" do to mastfoot pressure?

Sail shape also depends on what materials the sail is made from and the luff curve in relation to the mast.

Yes more downhaul will push the shape further forward and then will start to flatter the sails shape at a certain point.
Outhaul really does depend on the seam shape cut into the panels and also batten tension will help to push shape into the sail as in most cases seams are shaped under the battens and when a batten is tensioned properly it helps push that shape into the sail more smoothly.

You can also over tension things and then you start loosing shape.

Usually outhaul flattens the sail and this works with downhaul.

Soz, I forgot to mention about outhaul. Personally I don't feel +outhaul moves the draft forward. Some add +outhaul to make the sail feel slightly less powerful when over powered. But for me, +outhaul is to improve upwind performance, +outhaul slightly tightens the leech hence better upwind angle.

+downhaul = draft moves forward
+outhaul = flatter sail and better upwind

bear mind I'm no pro and I'm basing this on my feeling from my sails, some might disagree.

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mikey100 said..
Have been trying to better understand sail trim and it's dynamics and have widely researched the applications of downhaul and outhaul on a sail's shape and I am finding some conflicting information in various windsurfing articles and videos on the subject. Have also gone to Australian Yachting lecture videos and asked local experienced sailors their opinion on the subject to try to understand. Have I got it right?
*more DOWNHAUL = draft forward
*more OUTHAUL = draft forward

Big topic. How long have you got?

When we add downhaul to a sail we bend the mast to match the sail's luffround. With minimum downhaul the leech is tight and the sail sets full for more lightwind power. The sail entry can be blunt, meaning the aerofoil shape does seem fuller further forwards. So 'less downhaul' can mean draft further forwards, which contradicts what you have heard.

When you add more downhaul to that same sail, the mast bends further, flattening the profile of the sail and usually releasing the leach at the head. That can mean the sail's pull actually moves aft. But this also depends on how the sail is cut, and some sails remain forward-pulling when fully downhauled. So, in that case, more downhaul 'can' mean draft forward.

But don't forget that when you add downhaul to a sail, you bend the mast and flatten the sail, and that usually means that a longer boom setting is required to get the correct outhaul. Outhaul is therefore in a conditional relationship with downhaul.


Outhaul, as an adjustment in its own right, is more simple - if you get your head around the basics.

A loose outhaul means the sail sets with a fuller belly for more power, but the lack of outhaul tension can mean a lack of panel tension in the lower sections of the sail, allowing the belly of the sail to distort in gusts. So, when powered up, adding outhaul tightens the lower leech and helps sail stability - and often restores forward drive in a backhanded sail.

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thedoor said..
what does "draft forward" do to mastfoot pressure?

The proper answer is 'nothing' .
But of course asking that question raises issues of stance as well as being about a rig setting.

Shall we mention about Center of Effort of where that goes. Or just keep it simple stupid

Different sails set differently.
Severne Turbo cammed sail. More downhaul = draft further forward and a deeper profile nearer the mast.
My Ezzy sails, cammed and no cammed, dont do that. They set flatter with more downhaul, but still with the CoE further forward with more outhaul & downhaul.
Ezzy did a video on how the profile changes, but I cant find that. It might have been part of an individual sail's rigging rather then a separate video and he has made loads of videos.

?t=44



ps, theory is just that. You need to change the settings on your sail and sail it and feel what difference it makes.

I found an Ezzy video which mentions draft and its relationship with downhaul and outhaul.
Not all sails have the same amount of seaming built into the sail, which is why different sails set and feel different.
7:43 into the video.
Too much downhaul flattens the sail too much and moves the draft back.
Adding outhaul flattens the sail and moves the draft forward.

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PhilUK said..
Different sails set differently.
Severne Turbo cammed sail. More downhaul = draft further forward and a deeper profile nearer the mast.
My Ezzy sails, cammed and no cammed, dont do that. They set flatter with more downhaul, but still with the CoE further forward with more outhaul & downhaul.
Ezzy did a video on how the profile changes, but I cant find that. It might have been part of an individual sail's rigging rather then a separate video and he has made loads of videos.

?t=44



ps, theory is just that. You need to change the settings on your sail and sail it and feel what difference it makes.

Watched that video. Have never seen a sail get MORE depth in the lower luff pocket with more downhaul. unless you let off positive outhaul to go neutral or negative. That does my head in.

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mikey100 said..

PhilUK said..
Different sails set differently.
Severne Turbo cammed sail. More downhaul = draft further forward and a deeper profile nearer the mast.
My Ezzy sails, cammed and no cammed, dont do that. They set flatter with more downhaul, but still with the CoE further forward with more outhaul & downhaul.
Ezzy did a video on how the profile changes, but I cant find that. It might have been part of an individual sail's rigging rather then a separate video and he has made loads of videos.

?t=44



ps, theory is just that. You need to change the settings on your sail and sail it and feel what difference it makes.

Watched that video. Have never seen a sail get MORE depth in the lower luff pocket with more downhaul. unless you let off positive outhaul to go neutral or negative. That does my head in.

I've not seen it either, which is why you have to keep an open mind about different sails as what works for one might not for another.

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mikey100 said..

PhilUK said..
Different sails set differently.
Severne Turbo cammed sail. More downhaul = draft further forward and a deeper profile nearer the mast.
My Ezzy sails, cammed and no cammed, dont do that. They set flatter with more downhaul, but still with the CoE further forward with more outhaul & downhaul.
Ezzy did a video on how the profile changes, but I cant find that. It might have been part of an individual sail's rigging rather then a separate video and he has made loads of videos.

?t=44



ps, theory is just that. You need to change the settings on your sail and sail it and feel what difference it makes.

Watched that video. Have never seen a sail get MORE depth in the lower luff pocket with more downhaul. unless you let off positive outhaul to go neutral or negative. That does my head in.

The bigger Point7 AC-1 sails from 2014-5, when rigged on the Point7 mast, will seem to drive the draft lower and deeper when taken from minimal usable downhaul to fully downhauled. I haven't actually measured though, and it may be an illusion of contrast, because the top of the sail twists way off and goes completely flat when fully downhauled, while the bottom of the sail just gets tighter skin tension without the depth moving. That's kinda what I'd expect when rigging a hardtop sail on a flextop mast, but the Point7 mast isn't supposed to be all that softtopped. What is true is that the sail will tolerate a ridiculous amount of wind at full downhaul without seeming to lose any bottom-end power. If they weren't so freakin' heavy I'd use them all the time...

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Awalkspoiled said..

mikey100 said..

PhilUK said..
Different sails set differently.
Severne Turbo cammed sail. More downhaul = draft further forward and a deeper profile nearer the mast.
My Ezzy sails, cammed and no cammed, dont do that. They set flatter with more downhaul, but still with the CoE further forward with more outhaul & downhaul.
Ezzy did a video on how the profile changes, but I cant find that. It might have been part of an individual sail's rigging rather then a separate video and he has made loads of videos.

?t=44



ps, theory is just that. You need to change the settings on your sail and sail it and feel what difference it makes.

Watched that video. Have never seen a sail get MORE depth in the lower luff pocket with more downhaul. unless you let off positive outhaul to go neutral or negative. That does my head in.

The bigger Point7 AC-1 sails from 2014-5, when rigged on the Point7 mast, will seem to drive the draft lower and deeper when taken from minimal usable downhaul to fully downhauled. I haven't actually measured though, and it may be an illusion of contrast, because the top of the sail twists way off and goes completely flat when fully downhauled, while the bottom of the sail just gets tighter skin tension without the depth moving. That's kinda what I'd expect when rigging a hardtop sail on a flextop mast, but the Point7 mast isn't supposed to be all that softtopped. What is true is that the sail will tolerate a ridiculous amount of wind at full downhaul without seeming to lose any bottom-end power. If they weren't so freakin' heavy I'd use them all the time...

You might want to consider an ACX. I know, it has no cams, but the amount of wind my Point 7 ACX can tolerate is quite ridiculous and it is a very fast sail. It is a less technical sail than the AC1 of course, but with 6.0 and 6.5, almost always sailed overpowered, I just rig on one down haul setting, and move the out haul maybe 2 cm. Or get an ACZ. Two under the boom cams and light.

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mikey100 said..

PhilUK said..
Different sails set differently.
Severne Turbo cammed sail. More downhaul = draft further forward and a deeper profile nearer the mast.
My Ezzy sails, cammed and no cammed, dont do that. They set flatter with more downhaul, but still with the CoE further forward with more outhaul & downhaul.
Ezzy did a video on how the profile changes, but I cant find that. It might have been part of an individual sail's rigging rather then a separate video and he has made loads of videos.

?t=44



ps, theory is just that. You need to change the settings on your sail and sail it and feel what difference it makes.

Watched that video. Have never seen a sail get MORE depth in the lower luff pocket with more downhaul. unless you let off positive outhaul to go neutral or negative. That does my head in.

I suppose the sail on the left could have had the 'correct' outhaul setting in that the boom was set at the right place, but as it didnt have enough downhaul that outhaul setting was a lot of positive outhaul pulling the sail flat. The sail on the right had the correct downhaul and boom set the same length, so in affect neutral outhaul letting the sail have the correct profile. But they didn't say if the outhaul settings were the same.

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duzzi said..

Awalkspoiled said..

mikey100 said..

PhilUK said..
Different sails set differently.
Severne Turbo cammed sail. More downhaul = draft further forward and a deeper profile nearer the mast.
My Ezzy sails, cammed and no cammed, dont do that. They set flatter with more downhaul, but still with the CoE further forward with more outhaul & downhaul.
Ezzy did a video on how the profile changes, but I cant find that. It might have been part of an individual sail's rigging rather then a separate video and he has made loads of videos.

?t=44



ps, theory is just that. You need to change the settings on your sail and sail it and feel what difference it makes.

Watched that video. Have never seen a sail get MORE depth in the lower luff pocket with more downhaul. unless you let off positive outhaul to go neutral or negative. That does my head in.

The bigger Point7 AC-1 sails from 2014-5, when rigged on the Point7 mast, will seem to drive the draft lower and deeper when taken from minimal usable downhaul to fully downhauled. I haven't actually measured though, and it may be an illusion of contrast, because the top of the sail twists way off and goes completely flat when fully downhauled, while the bottom of the sail just gets tighter skin tension without the depth moving. That's kinda what I'd expect when rigging a hardtop sail on a flextop mast, but the Point7 mast isn't supposed to be all that softtopped. What is true is that the sail will tolerate a ridiculous amount of wind at full downhaul without seeming to lose any bottom-end power. If they weren't so freakin' heavy I'd use them all the time...

You might want to consider an ACX. I know, it has no cams, but the amount of wind my Point 7 ACX can tolerate is quite ridiculous and it is a very fast sail. It is a less technical sail than the AC1 of course, but with 6.0 and 6.5, almost always sailed overpowered, I just rig on one down haul setting, and move the out haul maybe 2 cm. Or get an ACZ. Two under the boom cams and light.

Good call - ACZ is probably my dream sail, but prices in USA are nuts. I picked up the AC-1 8.6 and 9.3 in heavily used condition at a reasonable price but in retrospect would have been better off getting just one sail which suited me better. It's cool carrying a 9.3 when guys are on 5.5, but it's also kinda silly.

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Awalkspoiled said..

duzzi said..

Awalkspoiled said..

mikey100 said..

PhilUK said..
Different sails set differently.
Severne Turbo cammed sail. More downhaul = draft further forward and a deeper profile nearer the mast.
My Ezzy sails, cammed and no cammed, dont do that. They set flatter with more downhaul, but still with the CoE further forward with more outhaul & downhaul.
Ezzy did a video on how the profile changes, but I cant find that. It might have been part of an individual sail's rigging rather then a separate video and he has made loads of videos.

?t=44



ps, theory is just that. You need to change the settings on your sail and sail it and feel what difference it makes.

Watched that video. Have never seen a sail get MORE depth in the lower luff pocket with more downhaul. unless you let off positive outhaul to go neutral or negative. That does my head in.

The bigger Point7 AC-1 sails from 2014-5, when rigged on the Point7 mast, will seem to drive the draft lower and deeper when taken from minimal usable downhaul to fully downhauled. I haven't actually measured though, and it may be an illusion of contrast, because the top of the sail twists way off and goes completely flat when fully downhauled, while the bottom of the sail just gets tighter skin tension without the depth moving. That's kinda what I'd expect when rigging a hardtop sail on a flextop mast, but the Point7 mast isn't supposed to be all that softtopped. What is true is that the sail will tolerate a ridiculous amount of wind at full downhaul without seeming to lose any bottom-end power. If they weren't so freakin' heavy I'd use them all the time...

You might want to consider an ACX. I know, it has no cams, but the amount of wind my Point 7 ACX can tolerate is quite ridiculous and it is a very fast sail. It is a less technical sail than the AC1 of course, but with 6.0 and 6.5, almost always sailed overpowered, I just rig on one down haul setting, and move the out haul maybe 2 cm. Or get an ACZ. Two under the boom cams and light.

Good call - ACZ is probably my dream sail, but prices in USA are nuts. I picked up the AC-1 8.6 and 9.3 in heavily used condition at a reasonable price but in retrospect would have been better off getting just one sail which suited me better. It's cool carrying a 9.3 when guys are on 5.5, but it's also kinda silly.

I am in the US and I think that they are actually cheap. Keep in mind that you do not pay VAT, and they ship direct for little money (50 euro for one sail). Availability this year might be tricky, but for example an ACZ 6.8 is right now 577 Euros = $681, including shipment. Compare with, for example, a Severne Turbo 7.0 $850 + taxes.

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mikey100 said..

PhilUK said..
Different sails set differently.
Severne Turbo cammed sail. More downhaul = draft further forward and a deeper profile nearer the mast.
My Ezzy sails, cammed and no cammed, dont do that. They set flatter with more downhaul, but still with the CoE further forward with more outhaul & downhaul.
Ezzy did a video on how the profile changes, but I cant find that. It might have been part of an individual sail's rigging rather then a separate video and he has made loads of videos.

?t=44



ps, theory is just that. You need to change the settings on your sail and sail it and feel what difference it makes.

Watched that video. Have never seen a sail get MORE depth in the lower luff pocket with more downhaul. unless you let off positive outhaul to go neutral or negative. That does my head in.

That is probably due to luff curve with a stiffer mast base, its weird for sure.

As I continue to look at vids and articles on this subject, I have come across two vids on rigging the brands' race sails (Duotone and Point7) which both say that unless it is for extreme (survival) conditions, rig with the same downhaul all the time, and only the outhaul needs to vary. I owned Duotone Warps and agree with the above- never rig with different downhaul. Anyone else do the same?

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mikey100 said..
As I continue to look at vids and articles on this subject, I have come across two vids on rigging the brands' race sails (Duotone and Point7) which both say that unless it is for extreme (survival) conditions, rig with the same downhaul all the time, and only the outhaul needs to vary. I owned Duotone Warps and agree with the above- never rig with different downhaul. Anyone else do the same?

I'm still not sure but my experience isn't that long. My current cammed/race sail, which I use the most, is easiest to rig to the same downhaul because the luff sleeve looks a certain way. I could go by marks on the extension, but it has stretched a little after breaking in. Same with my uncammed sails. I am more inconsistent with reading the downhaul on the uncammed sail because the tightness of the leach isn't as obvious to me.

I will say, however, that having a rig with adjustable outhaul has made that effect much more clear, as I can add or drop outhaul while on the plane (mostly foiling), and immediately notice a difference. It seems like that alone has given me a better feel for how much outhaul matters. Really, 1cm of outhaul changes the feel of a sail noticeably. I have however also played around with downhaul settings on my smallest wave sail and now recognize when it's got too much downhaul, as it gets very twitchy, almost on-or-off feeling, then I backed off by loosening it and it was a much better experience.

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mikey100 said..
As I continue to look at vids and articles on this subject, I have come across two vids on rigging the brands' race sails (Duotone and Point7) which both say that unless it is for extreme (survival) conditions, rig with the same downhaul all the time, and only the outhaul needs to vary. I owned Duotone Warps and agree with the above- never rig with different downhaul. Anyone else do the same?

On a cambered sail, i never play with the downhaul. Only the outhaul. Altering the downhaul is only something i do at the start when im looking for the right settings for the sail, which can sometimes be frustrating when they play with the sail design season to season.

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mikey100 said..
As I continue to look at vids and articles on this subject, I have come across two vids on rigging the brands' race sails (Duotone and Point7) which both say that unless it is for extreme (survival) conditions, rig with the same downhaul all the time, and only the outhaul needs to vary. I owned Duotone Warps and agree with the above- never rig with different downhaul. Anyone else do the same?

There is a downhaul setting for a rig which will work well for everyone, and that's the one which gets the head twisting open to match the wind angle at the head of the sail. The sail head then has to interact with gusts to twist further to spill excess wind.

That recommended downhaul tension also tensions the luff panel and stabilises the sail's driving aerofoil shape

With that recommended downhaul setting you can then control available power using outhaul, because a slack outhaul gives more belly to the lower section of the sail. And then more outhaul flattens that sail belly, in particular at the rear and for the lower leach - and that should also reduce any backhandedness felt in the rig to keep it driving forwards.

But these are the basic ideas for people who don't really like tweaking their rig settings. If you are underpowered you can sail with a bit less downhaul, and that tightens the upper leach of the sail which can give you a bit more drive to help get planing.
Equally, if you are well overpowered and have already tightened outhaul, then adding a touch more downhaul may get you back in control, if it allows more of the sail head to twist off.

The other thing to say is that the sail shape changes when we hang off the rig, and the heavier guy loads the rig more and probably has more sideways mast bend than the lighter sailor. And so, with any sail brand, it's highly likely that different downhaul settings will work better for different weight sailors.


In summary, it's great that many modern rigs are just 'downhaul and go' with recommended settings, but you also have the chance of getting more range from any sail size by altering downhaul and outhaul settings - and what you find works for you trumps the manufacturer's recommendations.

It helps that you are not frightened of getting the downhaul on your sail. If you struggle with rigging then you might not want to make any subtle adjustments.

Have a draft and think about the draft

Without tension you can a huge bag with a centered pull location.

You add tension, the mast bends more up top and starts wrinkling the top and rear section of the sail. The draft moves forward.

The outhaul flattens the sail around the clew area and that also makes the draft moves forward.

Draft back more back have pressure, draft forward more balanced pressure.

When the sail fills with wind, the mast bends and sometimes the draft moves. Canbers helps keep the profile more steady.

Mikey,
Basher is correct. And you can probably tell there are significant differences between cammed vs camless sails and between different sails/brands. For cammed sails, depending on the sail's cut, the cams may have a bigger impact on draft shape and location than downhaul tension. There's obviously a ton of variables - cams, sail cut, mast characteristics, etc, etc.

Putting aside windsurfing sails for a moment, the basic theory of draft in sails is as follows:
- Wind following a curved surface (draft) produces forward force. The bigger the draft (within limits), the more power is produced. The center of the draft on the sail is the "Center of Effort", CoE.
- Light winds: the big danger is that wind-flow may become detached from the leeward side of the sail as the wind is not powerful enough to adhere. So sails are rigged with a flatter draft to maintain attached flow. Power produced is less but maintaining attached flow trumps everything else.
- Medium winds: the wind-flow is powerful enough to adhere to a more curved surface. So sails are rigged to their fullest draft to take advantage and maximize speed.
- High winds: assuming a small sail boat's limited ability to reduce the sail(rig) size, the biggest danger is getting overpowered. You counteract that by adjusting the settings to flatten the sail's draft to keep the boat sailing flat and from being over-powered.
- Point of sail: When sailing to windward, you can often improve your pointing by flattening the draft. Depending on the boat, a higher (slower, flatter draft) mode may get you to windward faster (called VMG, velocity made good) than a lower mode (faster, fuller draft).
When sailing off the wind, you don't have this trade off and want to maximize draft for speed.

Now how does that translate to windsurfing?
2 huge differences in the rig: a) given the u-joint, heeling is not an issue, and more importantly b) you introduce a super-bendable mast that allows a super-curved and adjustable luff shape. This allows windsurf sail draft to be adjusted to a degree not available in most sailboats.

Downhaul:
Adding more downhaul tension bends the mast around the cloth. In doing so, the mast tension flattens the draft. Depending on the cut, it may also move the draft back. Probably the best video demonstration I've seen of this is for the Sailworks Hucker, below. For this sail, adding downhaul both flattens the draft and moves it back, but the degree of flattening is much greater than the front-back movement.



Outhaul:
Once you have set the downhaul tension, adding more outhaul will flatten the draft further. The outhaul's impact on draft location will depend on the cut of the sail, so to my knowledge it's hard to make generalizations.

Ok. So keeping it simple:-
MORE DOWNHAUL = deepest draft position forward and lower. MORE OUTHAUL = deepest draft position forward.

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JCBoston said..

Now how does that translate to windsurfing?
2 huge differences in the rig: a) given the u-joint, heeling is not an issue, and more importantly b) you introduce a super-bendable mast that allows a super-curved and adjustable luff shape. This allows windsurf sail draft to be adjusted to a degree not available in most sailboats.

I'm not sure what boats you sail, but there are heaps of boats with more draft adjustment than a windsurfer. Not many sailmakers actually want a super-bendy mast in these days of low-stretch modern sailcloth, which is why boats like Moths use stays to restrict their bend - and get efficient sail shape through a far wider wind range than most windsurfer sails.

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Chris 249 said..

JCBoston said..

Now how does that translate to windsurfing?
2 huge differences in the rig: a) given the u-joint, heeling is not an issue, and more importantly b) you introduce a super-bendable mast that allows a super-curved and adjustable luff shape. This allows windsurf sail draft to be adjusted to a degree not available in most sailboats.

I'm not sure what boats you sail, but there are heaps of boats with more draft adjustment than a windsurfer. Not many sailmakers actually want a super-bendy mast in these days of low-stretch modern sailcloth, which is why boats like Moths use stays to restrict their bend - and get efficient sail shape through a far wider wind range than most windsurfer sails.

This^^^
i think why mikey has come across differing opinions on what draft movement involves is because most windsurfers relate draft movement to how a sail feels after pullling on downhaul/outhaul.

technically when (boat) sailors talk about draft, they are referring to the position of maximum draft in a sail. That is the position where the sail reaches maximum depth in its profile. And that is the textbook definition of maximum draft. Technically when you pull on downhaul, and outhaul you are always moving the draft back in the sail.


When windsurfers talk about draft, they are actually referring to a change of position of the Centre of pressure on the sail. As best i can figure out, this relation comes from windsurfers always sailing with a bigger difference in true wind to appparent wind direction, as opposed to boat sailors, who are used to sailing with much less of an apparent wind shift owing to slower speeds. When you pull on more downhaul and outhaul, the reason you experience less back hand pressure is because you've given the sail a finer entry, and removed some of the volume of draft from the sails profile. Basher eluded to that in his previous post.

As Chris249 said, boats with fully battened mainsails and flexible masts can shift the draft in their sails by quite drastic amounts, as compared to a windsurfing sail. They can move the draft in the mainsail from the front third of the sail, to somewhere much closer to the middle of the sails profile. But thats not to take away from what a windsurfing sail is. They are in many ways far superior for what a windsurfer requires, and some of the concepts (square top sails that lose leech tension with dowhaul) have been adapted across to boats that are capable of apparent wind sailing.

^ this++

Adding downhaul will move the draft back, but more noticeably, down. You'll feel the centre of effort to be lower and more stable, because leverage.

Just imagine it in your mind, and really exaggerate it; a totally straight mast and a banana. Where is the deepest point of the sail?

Adding outhaul reduces the depth of the shape, and thus the draft, and will move it slightly back even more. Same reason.

What you really want is:

1) Laminar flow
2) Control

Also, I'm always sailing upwind : D