Hi all,

I have for some time wondered about actually happens when a sails gets really overpowered.

A bit hard to describe, but when caught out with a sail really way too big I have to push the sail hard away from me with the front hand, like the rig wants to slam the mast in my face!

Backhand pressure does not change much, which to me indicates that the harness lines are sufficiently far back on the boom?

Moving the lines might alleviate some of this(?), but my gut feeling is that something else is happening here. I have experienced this with various no cam freeride/freerace sails. Does this occur with cambered sails also?

My guess is that when overpowered, the centre of effort (COE) of the sail moves aft of the harness lines. The rig pivots on the harness lines, the rear moving away and the front moves towards the sailor. The sailor counteracts by pushing out with the front hand and pulling in with the back hand. The effort is worse with no can sails as they are less stable and the COE moves more. If your harness lines are biased to the rear, it's easier to manage.

Yes. This is a symptom of the C of E moving back (and often up) in the sail by a significant amount.

It is much more prevelant in older sails, camless and soft wave type sails. Is is almost not present in modern cam'ed sails and far less prevelent on well designed modern Camless freeride sails with better designed seam shaping, dynamic twist and far better/stiffer battens.

It's either time to change down a sail size or two, or update your sail quiver.

Select to expand quote

dedekam said..
Hi all,

I have for some time wondered about actually happens when a sails gets really overpowered.

A bit hard to describe, but when caught out with a sail really way too big I have to push the sail hard away from me with the front hand, like the rig wants to slam the mast in my face!

Backhand pressure does not change much, which to me indicates that the harness lines are sufficiently far back on the boom?

Moving the lines might alleviate some of this(?), but my gut feeling is that something else is happening here. I have experienced this with various no cam freeride/freerace sails. Does this occur with cambered sails also?

Symmetrical foils such as typical fins produce lift at an aerodynamic centre which is approximately 25% of the chord back from the leading edge. Asymmetrical aerofoils such as cambered sails not only produce a lift vector, they also produce a pitching moment - the rig tries to rotate itself to a lower angle of attack. This pitching moment increases with deeper camber as well as increasing with wind velocity. To counteract this pitching moment you can flatten the sail or counteract it with a monet in the other direction, typically by moving your hands and or harness lines back on the boom

Thanks, sort of what I expected I guess.The sails in question are 2018 freerace sails which I am otherwise very happy with. My plan was to keep them for a long time, but your comments makes me consider changing the bigger sizes to twin cams. Hm.

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Pacey said..

Symmetrical foils such as typical fins produce lift at an aerodynamic centre which is approximately 25% of the chord back from the leading edge. Asymmetrical aerofoils such as cambered sails not only produce a lift vector, they also produce a pitching moment - the rig tries to rotate itself to a lower angle of attack. This pitching moment increases with deeper camber as well as increasing with wind velocity. To counteract this pitching moment you can flatten the sail or counteract it with a monet in the other direction, typically by moving your hands and or harness lines back on the boom

Aha! This describes precisely what I experience.

Very interesting because I tend to rig my sails with as much camber as possible, in an effort to stabilize the CoE (since I don't have cambers) but from what you say flattening the sail would actually help.

I wouldn't go changing to twin cams from 2018 free race sails if youre seeking stability.


Sail design has indeed improved across the board over the years, but a modern free race is still a helluva lot more stable than a modern twin cam. A twin cam will give you earlier (Or should i say easier) planing Size for size, but youll be overpowered on it 5knots sooner than a free race sail.

Select to expand quote

dedekam said..
Thanks, sort of what I expected I guess.The sails in question are 2018 freerace sails which I am otherwise very happy with. My plan was to keep them for a long time, but your comments makes me consider changing the bigger sizes to twin cams. Hm.

Stating the obvious: do increase the down haul if you are grossly overpowered. And of course it depends on the sail. My Point-7 ACX 6.5 has been out ridiculously overpowered and it never shows any signs like you describe ... it actually feels lighter when overpowered. Only sails I experienced something similar to what you describe are Hot Sails Maui 3 and 4 battens. The front collapsing and trying to back wind if overpowered ... tightening up everything helped somewhat, but of course these are pure wave sails, not freerace. I am considering an AC-Z twin (under boom) cams but i am not sure why, it is probably for the fun of going back to cams

A tight leach 9.5 Raceboard sail in 20kts+ will give you exactly the sensation you describe. When severly overpowered its almost impossible to bear off. Itll drive you so far upwind. Really feels like the front third of sail is doing nothing but trying to throw you backwards.

I set my 4 batten wave sails to have the back hand between the lines when powered up. Keeps them from getting really back handed during the gusts and I mostly sail with the front hand.
Also keeps me from overpowering the fins.

What I'm finding with the OD's is they never really get that overpowered/heavy back hand feeling unless your trying to slow things down. If you just bear off and go with it they just seem to go faster and get lighter in the hands. Problem is you Can end up going much faster than you really want to.
its a bit like going faster over chop is actually easier that going slow with the down side of when things do go wrong they go really wrong and you end up with body size holes in your sails

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Ben1973 said..
What I'm finding with the OD's is they never really get that overpowered/heavy back hand feeling unless your trying to slow things down. If you just bear off and go with it they just seem to go faster and get lighter in the hands. Problem is you Can end up going much faster than you really want to.
its a bit like going faster over chop is actually easier that going slow with the down side of when things do go wrong they go really wrong and you end up with body size holes in your sails

To a degree its this^^^ with a race sail. there is still a top end to them where they'll try to twist open, but generally a lot higher than you think. If you sit up, thats when you'll start to feel overloaded.

The ability for a sail to be comfortable when overpowered is very dependant on what type of sail it is. Full cambered Race sails are designed with very high tensions, more battens ,often carbon, and cambers. They are designed to be sailed at the top of thier wind range and will be more comfortable when doing so the draft being very stable. The description " freerace sails" does cover a pretty big range of design types and the sails can vary alot in this group. Can you tell us what sails they are?
Clearly when overpowered the first port of call is more downhaul but you will get to a point where the sail s just too big. If you want to do some modifications to increase the wind range it is possible. You can fit stiffer battens ( make sure the leading edge is not too stiff as it will flatten the profile) Battens that are stiffer will help combat the draft moving rearward. If they are Rod battens not tubes you can slide some tube over the back 60% of the rod on some of the battens, start with the midsail battens. If you have tube battens check if they are carbon ( unlikely on a freerace sail) and consider changing the tube section to carbon .
These things will help but there is always a point where the sail is just too big for you and you need to be on a smaller size.
You could consider changing the larger size to a Race sail. This does come with some tradeoffs though. They are physically heavier and harder to pump. they can lack some bottom end power because of this compared to a 'softer sail " of the same size.
So you have options but knowing what sails they are woud be helpful to give you meaningful advice.

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Subsonic said..

Ben1973 said..
What I'm finding with the OD's is they never really get that overpowered/heavy back hand feeling unless your trying to slow things down. If you just bear off and go with it they just seem to go faster and get lighter in the hands. Problem is you Can end up going much faster than you really want to.
its a bit like going faster over chop is actually easier that going slow with the down side of when things do go wrong they go really wrong and you end up with body size holes in your sails

To a degree its this^^^ with a race sail. there is still a top end to them where they'll try to twist open, but generally a lot higher than you think. If you sit up, thats when you'll start to feel overloaded.

Does that vary with sailor weight? Eg- a c60kg sailor won't have them twisting off properly because they don't use the sail in enough wind?? or it doesn't make any difference?
I see the sails twist heaps in photos of the big guys but I don't think it does with me?

Select to expand quote

dedekam said..
Hi all,

I have for some time wondered about actually happens when a sails gets really overpowered.

A bit hard to describe, but when caught out with a sail really way too big I have to push the sail hard away from me with the front hand, like the rig wants to slam the mast in my face!

Backhand pressure does not change much, which to me indicates that the harness lines are sufficiently far back on the boom?

Moving the lines might alleviate some of this(?), but my gut feeling is that something else is happening here. I have experienced this with various no cam freeride/freerace sails. Does this occur with cambered sails also?

I find that.. When I'm in survival conditions or a bit worried I end up with my front hand right next to the mast ready to push away on the boom..?

Basically as I suggest in my faq section (windsurfing.lepicture.com/tips-and-tricks/) if the sail lacks downhaul tension the pull will come from too high up. In order to keep control, tension must be added until the sail opens up around the harness lines without distorting or coe moving around.

Outhaul tension may help control the coe also. A sail overly tensioned with be a bit crazy, very direct and moving around a lot although lighter in the hands.

Pure survival mode, you may need to tuck your front elbow right against your hip to be able to hold the sail up.

When completely overpowered basically the wind just want to flatten the sail so imagine the draft of the sail and how it evolves when well powered. Look at the profile, pump it on the beach and it'll give you an idea on how it performs.

The higher the draft the more mast flex, the more it may want to pull you. The lower the draft the more control, speed with a slight less grunt down low.

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Subsonic said..
I wouldn't go changing to twin cams from 2018 free race sails if youre seeking stability.

Sail design has indeed improved across the board over the years, but a modern free race is still a helluva lot more stable than a modern twin cam. A twin cam will give you earlier (Or should i say easier) planing Size for size, but youll be overpowered on it 5knots sooner than a free race sail.

Is this really true? I thought the main point of cambered sails is the stability they provide?
A stiffer and deeper profile makes it harder to depower, but to me that is not quite the same.

Select to expand quote

mr love said..
The ability for a sail to be comfortable when overpowered is very dependant on what type of sail it is. Full cambered Race sails are designed with very high tensions, more battens ,often carbon, and cambers. They are designed to be sailed at the top of thier wind range and will be more comfortable when doing so the draft being very stable. The description " freerace sails" does cover a pretty big range of design types and the sails can vary alot in this group. Can you tell us what sails they are?
Clearly when overpowered the first port of call is more downhaul but you will get to a point where the sail s just too big. If you want to do some modifications to increase the wind range it is possible. You can fit stiffer battens ( make sure the leading edge is not too stiff as it will flatten the profile) Battens that are stiffer will help combat the draft moving rearward. If they are Rod battens not tubes you can slide some tube over the back 60% of the rod on some of the battens, start with the midsail battens. If you have tube battens check if they are carbon ( unlikely on a freerace sail) and consider changing the tube section to carbon .
These things will help but there is always a point where the sail is just too big for you and you need to be on a smaller size.
You could consider changing the larger size to a Race sail. This does come with some tradeoffs though. They are physically heavier and harder to pump. they can lack some bottom end power because of this compared to a 'softer sail " of the same size.
So you have options but knowing what sails they are woud be helpful to give you meaningful advice.

You bring up an interesting aspect of sail design not often mentioned, but surely you open a can of worms modifying a sail too that degree(?)

My solution is to cover all sizes, but on that day I was nearing the end of my session anyway so I didn't bother going ashore and change down. Adding a big race sail with less bottom might just produce an overlap with the smaller free race sails. That is why I was thinking of twin cams. However the input I get here makes it clear to me that I need to play more with downhaul/outhaul combinations.

Select to expand quote

dedekam said..

Subsonic said..
I wouldn't go changing to twin cams from 2018 free race sails if youre seeking stability.

Sail design has indeed improved across the board over the years, but a modern free race is still a helluva lot more stable than a modern twin cam. A twin cam will give you earlier (Or should i say easier) planing Size for size, but youll be overpowered on it 5knots sooner than a free race sail.

Is this really true? I thought the main point of cambered sails is the stability they provide?
A stiffer and deeper profile makes it harder to depower, but to me that is not quite the same.

In my experience yes, its absolutely true.

Lots of good input here, thanks all. I now have a better understanding of what goes on when a sail gets totally overpowered, very useful.

Select to expand quote

sboardcrazy said..

Subsonic said..

Ben1973 said..
What I'm finding with the OD's is they never really get that overpowered/heavy back hand feeling unless your trying to slow things down. If you just bear off and go with it they just seem to go faster and get lighter in the hands. Problem is you Can end up going much faster than you really want to.
its a bit like going faster over chop is actually easier that going slow with the down side of when things do go wrong they go really wrong and you end up with body size holes in your sails

To a degree its this^^^ with a race sail. there is still a top end to them where they'll try to twist open, but generally a lot higher than you think. If you sit up, thats when you'll start to feel overloaded.

Does that vary with sailor weight? Eg- a c60kg sailor won't have them twisting off properly because they don't use the sail in enough wind?? or it doesn't make any difference?
I see the sails twist heaps in photos of the big guys but I don't think it does with me?

Use a softer mast, for example I can rig the 7.8od on the severne 490 mast but it get to be a handful much earlier than it does with the softer 460mast

I find that sails tend to overpower in different ways, depending on the design and intended use.

But, if I can add some generalisations here, the basic issue starts when you reach the limit of sail twist.

All our modern sails are designed to set with some twist and that's so the angle of attack of the luff at each level of sail height can align with and deflect the wind, and this is how the sail generates maximum lift or power for it's sail size.

Our sails then go one stage further by depowering as a gust hits or as we use the same rig in increasing wind. Basically, the head of the sail twists open to release the drive from that upper section of the rig. A sail with the upper panels cut flat 'sheets out' independently of the lower section of the rig and the sail head would flutter like a flag if it wasn't held flat by the head battens.

That open sail head is no longer driving the board and adds a small amount of drag, but that drag is outweighed by the drive from the rest of the sail as long as we can stay sheeted in at boom level. Being overpowered is where the drag from the upper part of the rig starts to outweigh the drive from the lower part of the sail.

As more and more of the upper sail is effectively sheeted out, the demands on the lower part of the rig are greater, and distortion over the lower panels often means the sail becomes more back handed.
You can try and reduce that distortion by adding more outhaul, and maybe downhaul, but if you flatten the sail completely then it loses it aerofoil shape - and its drive.

If you have a sail that has fullness cut in the head - as with many light wind race sails - then twist at the head is limited and those sails can soon reach their top end. With shape in the top batten, the drag from that section is increased as the sail head tries to twist open.
And you may even find that the drive from the sail head reverses, giving you extra handling problems where there is a force to windward from the head of the sail. So in a gust you find you are dumped in to the windward side of the board.


The key points when sailing overpowered are:
1) Keeping moving fast if you can, as this reduces pressure on the sail.
2)Add downhaul if the sail is not twisting open properly.
3) You should always use positive outhaul when sailing overpowered as that helps stabilise the sail's lower panels.
4) With many rigs the centre of effort will move back a bit as the wind increases, so you may need to shift your harness lines back on the boom.
5) In windy weather it's often better to be on a smaller sail with a relatively big board, than it is to be on too big a sail fitted to a relatively small or sinky board.
6) Practice sailing in windy weather as this will make it easier to handle the conditions, and experience will also help you in making better rig and board size choices.

Select to expand quote

sboardcrazy said..

dedekam said..
Hi all,

I have for some time wondered about actually happens when a sails gets really overpowered.

A bit hard to describe, but when caught out with a sail really way too big I have to push the sail hard away from me with the front hand, like the rig wants to slam the mast in my face!

Backhand pressure does not change much, which to me indicates that the harness lines are sufficiently far back on the boom?

Moving the lines might alleviate some of this(?), but my gut feeling is that something else is happening here. I have experienced this with various no cam freeride/freerace sails. Does this occur with cambered sails also?

I find that.. When I'm in survival conditions or a bit worried I end up with my front hand right next to the mast ready to push away on the boom..?

I start to think, from what I read, that you are not using the sail as it should be used. A race or free race sail is designed to be used well powered to overpowered, they do not do what you describe. But a big part of the equation is to retain your asset on the board and loading the sail.

Your comment that you move the front hand "right next to mast" is an indication that you are disrupting the proper position of the sail. Similarly with your observation that you do not see the top of the sail twist. It is a bit hard to quantify twist while you are sailing but you need to load the sail to see twist.

What I think is happening is that in windy conditions you unload the sail, and then the inevitable happens: the sail looses the forward vector and it is just a matter of time until it gets back winded.

Select to expand quote

duzzi said..

sboardcrazy said..

dedekam said..
Hi all,

I have for some time wondered about actually happens when a sails gets really overpowered.

A bit hard to describe, but when caught out with a sail really way too big I have to push the sail hard away from me with the front hand, like the rig wants to slam the mast in my face!

Backhand pressure does not change much, which to me indicates that the harness lines are sufficiently far back on the boom?

Moving the lines might alleviate some of this(?), but my gut feeling is that something else is happening here. I have experienced this with various no cam freeride/freerace sails. Does this occur with cambered sails also?

I find that.. When I'm in survival conditions or a bit worried I end up with my front hand right next to the mast ready to push away on the boom..?

I start to think, from what I read, that you are not using the sail as it should be used. A race or free race sail is designed to be used well powered to overpowered, they do not do what you describe. But a big part of the equation is to retain your asset on the board and loading the sail.

Your comment that you move the front hand "right next to mast" is an indication that you are disrupting the proper position of the sail. Similarly with your observation that you do not see the top of the sail twist. It is a bit hard to quantify twist while you are sailing but you need to load the sail to see twist.

What I think is happening is that in windy conditions you unload the sail, and then the inevitable happens: the sail looses the forward vector and it is just a matter of time until it gets back winded.

What do you mean by 'asset'. I've seen that used in overseas posts..do you mean stance?
Re sail twist I'm talking of looking at photos or videos of me sailing not looking up.
When I say my front hand gets close to the mast..it's more a psychological thing. I don't know if I have needed to push (?) but it's there in case I need to .
I don't think I sheet out but I'll take note next time.
I have an adjustable outhaul and use that to extend the sails range..I usually downhaul to specs so the sails rotate and rely on the outhaul on the water.
I can't pull more on unless I come back to the launch..The sails luff is generally loose to the boom.( 3 cammed Overdrives)..
I might try moving my lines back next time and see if that helps..
I was watching one of those videos by Cookie ( I think it was him) and he said in overpowering conditions he moves his lines forward so he's not using the full power of the sails..Though he is on small kit with non cammed light 3.7m sails ..

Select to expand quote

sboardcrazy said..

dedekam said..
Hi all,

I have for some time wondered about actually happens when a sails gets really overpowered.

A bit hard to describe, but when caught out with a sail really way too big I have to push the sail hard away from me with the front hand, like the rig wants to slam the mast in my face!

Backhand pressure does not change much, which to me indicates that the harness lines are sufficiently far back on the boom?

Moving the lines might alleviate some of this(?), but my gut feeling is that something else is happening here. I have experienced this with various no cam freeride/freerace sails. Does this occur with cambered sails also?

I find that.. When I'm in survival conditions or a bit worried I end up with my front hand right next to the mast ready to push away on the boom..?

Don't worry about the front hand thing. I dont. I put a video of myself up on another forum and someone commented on my front hand, suggesting I hadn't rigged the sail correctly or I was nervous of being catapulted or some such nonsense. The person who made the comment hadn't gone over 26 knots on iSonics & race sails, I had knicknamed him Captain Slow.
I put it down to having a long arms to body length ratio, putting my lines quite far back so in the gusts its balanced. At 1 point I had tennis elbow and having a straight arm helped with that. It just feels comfortable to put my hands where they are.

Take a look at Andy Laufer here. His hand is nearly at the mast! Quite extreme in this video. In his other videos his hand is still quite far forward.
Someone asked him in the comments on youtube why his hand is so far forward and it was because his lines are so far back. I cant find the comment now. He is ranked 7th on the gps-speedsailing website, so he knows what he is doing. Andy puts up some really good videos of slalom blasting, well worth a look.
Lena Erdil also has her front hand quite far forward.

Select to expand quote

Subsonic said..

dedekam said..

Subsonic said..
I wouldn't go changing to twin cams from 2018 free race sails if youre seeking stability.

Sail design has indeed improved across the board over the years, but a modern free race is still a helluva lot more stable than a modern twin cam. A twin cam will give you earlier (Or should i say easier) planing Size for size, but youll be overpowered on it 5knots sooner than a free race sail.

Is this really true? I thought the main point of cambered sails is the stability they provide?
A stiffer and deeper profile makes it harder to depower, but to me that is not quite the same.

In my experience yes, its absolutely true.

The primary reason for cams, is for stability; it is exactly the reason they are used in Race and Speed sails, as you want to hang on to the biggest sail you can.. even past the point of overpowered/back-winding. Choosing a free-race sail (no-cam) over a cam'ed sail, is wrong [ if your goal is stability ].

Select to expand quote

mathew said..
The primary reason for cams, is for stability; it is exactly the reason they are used in Race and Speed sails, as you want to hang on to the biggest sail you can.. even past the point of overpowered/back-winding. Choosing a free-race sail (no-cam) over a cam'ed sail, is wrong [ if your goal is stability ].

Exactly.

If subsonics twin cam was not stable, it was a crappy design. Try a KA Koncept (3 cam).

Select to expand quote

mathew said..

Subsonic said..

dedekam said..

Subsonic said..
I wouldn't go changing to twin cams from 2018 free race sails if youre seeking stability.

Sail design has indeed improved across the board over the years, but a modern free race is still a helluva lot more stable than a modern twin cam. A twin cam will give you earlier (Or should i say easier) planing Size for size, but youll be overpowered on it 5knots sooner than a free race sail.

Is this really true? I thought the main point of cambered sails is the stability they provide?
A stiffer and deeper profile makes it harder to depower, but to me that is not quite the same.

In my experience yes, its absolutely true.

The primary reason for cams, is for stability; it is exactly the reason they are used in Race and Speed sails, as you want to hang on to the biggest sail you can.. even past the point of overpowered/back-winding. Choosing a free-race sail (no-cam) over a cam'ed sail, is wrong [ if your goal is stability ].

I think someones missed something somewhere, and im not sure who. Most of the free race sails i know of are in fact cambered, and are only a brief step away from full race.

A Severne overdrive as an example is a wide pocket 3cam free race. They are practically a race sail, but they lack that tiny bit of top end stability that a 4cam race sail has. Other brands have similar sails in there selection. There are sails like say an NCX which has no cams, and severne turbo which is a twin cam/small luff pocket. but i wouldn't call them free "race". They fall into the category of fast free ride and lack the top end stability that a free race or race sail has.

Select to expand quote

sboardcrazy said..

duzzi said..

sboardcrazy said..

dedekam said..
Hi all,

I have for some time wondered about actually happens when a sails gets really overpowered.

A bit hard to describe, but when caught out with a sail really way too big I have to push the sail hard away from me with the front hand, like the rig wants to slam the mast in my face!

Backhand pressure does not change much, which to me indicates that the harness lines are sufficiently far back on the boom?

Moving the lines might alleviate some of this(?), but my gut feeling is that something else is happening here. I have experienced this with various no cam freeride/freerace sails. Does this occur with cambered sails also?

I find that.. When I'm in survival conditions or a bit worried I end up with my front hand right next to the mast ready to push away on the boom..?

I start to think, from what I read, that you are not using the sail as it should be used. A race or free race sail is designed to be used well powered to overpowered, they do not do what you describe. But a big part of the equation is to retain your asset on the board and loading the sail.

Your comment that you move the front hand "right next to mast" is an indication that you are disrupting the proper position of the sail. Similarly with your observation that you do not see the top of the sail twist. It is a bit hard to quantify twist while you are sailing but you need to load the sail to see twist.

What I think is happening is that in windy conditions you unload the sail, and then the inevitable happens: the sail looses the forward vector and it is just a matter of time until it gets back winded.

What do you mean by 'asset'. I've seen that used in overseas posts..do you mean stance?
Re sail twist I'm talking of looking at photos or videos of me sailing not looking up.
When I say my front hand gets close to the mast..it's more a psychological thing. I don't know if I have needed to push (?) but it's there in case I need to .
I don't think I sheet out but I'll take note next time.
I have an adjustable outhaul and use that to extend the sails range..I usually downhaul to specs so the sails rotate and rely on the outhaul on the water.
I can't pull more on unless I come back to the launch..The sails luff is generally loose to the boom.( 3 cammed Overdrives)..
I might try moving my lines back next time and see if that helps..
I was watching one of those videos by Cookie ( I think it was him) and he said in overpowering conditions he moves his lines forward so he's not using the full power of the sails..Though he is on small kit with non cammed light 3.7m sails ..

What happens is that you are getting overpowered by the sail. Your body is lifted up from the proper position and a result the sail is unloaded. You loose speed (even if it feels the opposite!), the sail keeps propelling forward but it does not release any longer. It becomes a much more rigid surface that keeps going but it will either catapult you or get back winded ...

The sail you own is perfectly fine, as most proper freerace sails (cammed or non-cammed) would be. You could take a Severne Overdrive to Luderitz and be ok. Forget line position, hand position and looking at the twist. With a race/freerace you have to commit, and that takes some technique and bit of guts when overpowered. You also need the proper board to go with it ... if you are on a slower freeride board it is not going to work ...

Select to expand quote

duzzi said..

sboardcrazy said..

duzzi said..

sboardcrazy said..

dedekam said..
Hi all,

I have for some time wondered about actually happens when a sails gets really overpowered.

A bit hard to describe, but when caught out with a sail really way too big I have to push the sail hard away from me with the front hand, like the rig wants to slam the mast in my face!

Backhand pressure does not change much, which to me indicates that the harness lines are sufficiently far back on the boom?

Moving the lines might alleviate some of this(?), but my gut feeling is that something else is happening here. I have experienced this with various no cam freeride/freerace sails. Does this occur with cambered sails also?

I find that.. When I'm in survival conditions or a bit worried I end up with my front hand right next to the mast ready to push away on the boom..?

I start to think, from what I read, that you are not using the sail as it should be used. A race or free race sail is designed to be used well powered to overpowered, they do not do what you describe. But a big part of the equation is to retain your asset on the board and loading the sail.

Your comment that you move the front hand "right next to mast" is an indication that you are disrupting the proper position of the sail. Similarly with your observation that you do not see the top of the sail twist. It is a bit hard to quantify twist while you are sailing but you need to load the sail to see twist.

What I think is happening is that in windy conditions you unload the sail, and then the inevitable happens: the sail looses the forward vector and it is just a matter of time until it gets back winded.

What do you mean by 'asset'. I've seen that used in overseas posts..do you mean stance?
Re sail twist I'm talking of looking at photos or videos of me sailing not looking up.
When I say my front hand gets close to the mast..it's more a psychological thing. I don't know if I have needed to push (?) but it's there in case I need to .
I don't think I sheet out but I'll take note next time.
I have an adjustable outhaul and use that to extend the sails range..I usually downhaul to specs so the sails rotate and rely on the outhaul on the water.
I can't pull more on unless I come back to the launch..The sails luff is generally loose to the boom.( 3 cammed Overdrives)..
I might try moving my lines back next time and see if that helps..
I was watching one of those videos by Cookie ( I think it was him) and he said in overpowering conditions he moves his lines forward so he's not using the full power of the sails..Though he is on small kit with non cammed light 3.7m sails ..

What happens is that you are getting overpowered by the sail. Your body is lifted up from the proper position and a result the sail is unloaded. You loose speed (even if it feels the opposite!), the sail keeps propelling forward but it does not release any longer. It becomes a much more rigid surface that keeps going but it will either catapult you or get back winded ...

The sail you own is perfectly fine, as most proper freerace sails (cammed or non-cammed) would be. You could take a Severne Overdrive to Luderitz and be ok. Forget line position, hand position and looking at the twist. With a race/freerace you have to commit, and that takes some technique and bit of guts when overpowered. You also need the proper board to go with it ... if you are on a slower freeride board it is not going to work ...

Here I'm on a board 50ltres over my weight in wind gusting to 30kts ..luckily the chop wasn't too big.. It's a freeride non cammed sail - 1st use..
I'm in survival mode crouching down low near the water and weighting the windward rail . The wind was threatening to lift the kit and throw me.. In the upwind bits I'm just trying to keep in one piece/on the water and I only power on when there's a bit of a lull..
Tiring but I had a ball..
I had to use the big board because of the big lulls. .Every now and then I'd swap to the waveboard which was a better fit but the lulls made that a bit dodgy to use..
I've since bought a 90ltre version of the big board which should be perfect in those conditions..

A few years ago Boards mag compared cammed and rotational from same manufacturers and found cammed had better top-end and rotational better bottom end which they thught due to different cuts and springiness of rotational easier to pup onto plan.