I own four Severne Convert sails and I was happy with them until I came back from a vacation at Maui. I rented Hot sails Firelight and didn't notice anything special about them. Was so windy that I did not have much mental capacity left for assessing the sail performance. However, when I came back to my own sails I noticed how they "screwed" themselves into the wind during the gusts. I had to push with the front arm to keep the angle of attack, or else, the sail would "over open" and almost knock me into the water while all speed was killed. I am guessing the pressure center moves backwards in the gusts.

I was told this happens with lightweight sails with fewer battens. My 6.7 has 5 battens.

I therefore borrowed two stiffer 6.5 m2 sails: Severne Gator (5 battens) and Severne NCX (7 battens). I have them rigged with the correct downhaul and the correct outhaul. They both show the same tendency of unstability in the gusts as described above.

Is this happening to you guys?
Why is it happening?
What is the phenomena called?
Are there sails that are more robust against this unstability?

(My skill level: water starts most of the time. Hooked in and planing, but having a hard time planing upwind. Gybes in less than 7 m/s. Tacks are very good. Footstraps sometimes, but not comfortably. Still on my Starboard Go 195, but I am also enjoying my Fanatic Gecko 133 in over 8 m/s)

Keep practising and learning. You have a long path ahead of you. It's not the sails. Its rigging, sail and board selection, and time on water. Befriend other more advanced sailors and learn from them.

Also your thread title is inflamatory. Consider editing it.

Harness lines too far forward? Enough downhaul? Never used the convert, but the NCX needs lots of downhaul.

No the harness lines are perfectly in the pressure center. I can ride almost hands free in steady wind, but in a gust, the sail twists.

I have tried with 1 cm more downhaul than recommended. Still the same.

Try backing off the outhaul a bit. I normally use the recommended downhaul or + 1 or 2 cms and use less 2 cm less outhaul. You need a bit of fullness in the sail for stability. Need to match sail size to board and experiment with the mast track a bit.

I agree with Dean above. I use 2017 NCX sails with old constant curve masts and personally I find that they are most stable with less downhaul, I rig them with the front end of the batten anywhere within the front half of the mast when viewed from the side (tuned to the conditions). I also set the boom length to be 2cm less than spec and the outhaul to be neutral. NCX's still work really well across a broad wind range because they can detuned with heaps of downhaul and outhaul, but for me they can become a bit twitchy at the front when they are pulled really tight and need a little more management.

Are you positive it's just the sail(s)?
Different boards and different fins can make the entire thing feel or act different.
Were you using the same board(s), and fin(s) as at home?
Also your angle of attack may have been a bit different than what you usually do at home.

I am wondering if Mastbender may be right.
I have Overdrives (Larger sizes ) and Gators (Smaller sizes ) mostly. Not really by design, just as I have found second hand gear for sale.
Love the Overdrives on my Futura 134. Tried the 7.0 Gator on the Futura on a choppy day and hated it. To the point that I was going to ditch it, so I bought an older 7.0m Turbo to replace it.
However have recently used the 7.0 Gator on my Carve 133 in similar choppy conditions and it was excellent.
I have Severne masts and rig downhaul to spec and mostly a bit less outhaul on the OD's and a cm or so less on the Gators mostly.

Not sure if you are describing the same thing, but when hit with a gust which is way beyond the sails range, a sail will tend to lock into an upwind position and be very difficult to sheet in or out, and it becomes difficult to bear away.
A gust within the sails range should not be an issue, and a correctly rigged sail on the right mast should have a relatively neutral feel.
Agree with Mastbender, Sails can work differently on different boards and fins.
Sailing with a severne Gt Turbo 8.1m on a starboard Atomiq 120l, the sail under performed and did not go up wind very well. Swapped to a Severne fox 120l board with same sail and same fin and the sail works perfectly . Nothing wrong with the AtomIQ, just doesn't like this sail fin combo.
I have 2017 Gators in 6.5 and 5.7 and they are awesome in my opinion, and i have not noticed any issues in gusts, other than the smile on my face broadens, and the urge to scream yeeha builds

So Winglet are you a light person? And are your sails cambered?
I'm 65kg, and I have the same problem with a lot of larger uncambered sails.
In the wind range I want to use them, they aren't fully turned on, a stronger gust will fully rotate them and move the centre of effort further back, making them almost impossible to use. Heavier guys using them in stronger winds don't have this problem.

I also notice even with most cambered sails, the centre of effort does move slightly backwards with stronger wind. Modern sails are designed to have a Reflex effect, where the boom batten rests on the back of the boom, this acts as a cantilever and helps keep the shape forward. I think that's why less outhaul is more stable, it allows this batten on boom thing to happen earlier.
So the difference could be in the width of the rear of your boom. If it's wide there, you won't be getting the same reflex effect, as the batten may not even touch the boom.

The slower you sail, the less stable sails will feel in gusts. Since you are not comfortable in the footstraps, your speeds will be on the low side, which means you feel the gusts much more than better sailors. As you get better, your sails will start feeling more stable.

There are several things that cause this. One is the change in the apparent wind angle in gusts. Another one is related to sheeting in. Typically, intermediate windsurfers are slower, and their sails are not fully sheeted in. When a gust hits, the change in apparent wind angle causes a lot more pressure on the back hand. When you (automatically) sheet out, the front of the sail gets backwinded, and you need to push hard with the front arm. There's a detailed discussion with diagrams of this at boardsurfr.blogspot.com/2011/01/sheet-in.html

The bottom line is that this is a technique issue much more than a sail issue (assuming that you rig your sails decently). For someone learning to be comfortable in the foot straps, a sail may have a narrow range from 8 to 10 m/s. Below 8, he can't plane and/or get in the straps; above 10, and he feels overpowered. An expert sailor might be reasonably comfortable on the same sail over a much wide wind range, perhaps from 6 to 12 m/s. Not that he'd necessarily sail the same sail over the entire range, but he could.

So if you have money to spend on windsurfing, investing into lessons rather than new sails will probably give you more bang for the buck. Plenty of good instructors on Maui, including Matt Pritchard. If there are none in your area, plan your next windsurf trip around a windsurf clinic, or at a resort with decent instructors.

Id have to agree with the rigging side of things. I use an 8m ezzy cheetah. Im always tuning for max power/ tighter leach. When wind strength increases past where i have sail set , the sail top will twist into the wind n try to push me in Backwards. I wrestle it for a bit as maybe the wind will back off. If it happens frequently its definately time to adjust rigging of sail. Usually more downhaul n a touch of outhaul solves the problem. In my experience All sails have this tendency when operating at upper wind limit for current level of rigging tension.

A 9 batten Maui race sail should fix the problem. Still need to rig them with enough down haul and outhaul if the winds up. The stiffness of the battens also plays a big part in the sail remaining stable. I once changed all the battens on a 5.7m Stuart Bell race sail with much,much stiffer battens from a 8.1m Tushingham Race sail and the difference in performance when it was windy was amazing. I cut the thin or flexible side of the battens to fit the smaller sail and it turned it into a flat frypan

Lighter guys do not have the weight or strength to make sails work when the sail is working above its capacity.

Technique and experience play a part too.

The old booms that had a plastic front end were useless too when the wind picked up.

boardsurfr is right its got to do with apparent wind and the resistance of the big board to move through the water with a light rider .best way to fix it is to rig the sail with a lot of down haul and flatten the out haul so it will dump the gust and not be so powerful,or run a smaller sail set for the gust,not the lull.
you dont say what board and fin you were using in maui, this will affect your sail as well as the winds are more stable there .if your harness lines are set for the lull a gust will back hand you ,so consider moving them back a bit and commit to the straps more on gust

Many good answers here! I definately beleive that going faster, being in the footstraps and sheeting in more will make Me less vulnerable to gusts as boardsurfr pointed out.

My weight is 78 kg.

Is this phenomena that I am talking about the same as being overpowered? In Norway, it is called "being screwed", as the sail wants to do a screw motion.

Select to expand quote

Winglet said..
Many good answers here! I definately beleive that going faster, being in the footstraps and sheeting in more will make Me less vulnerable to gusts as boardsurfr pointed out.

My weight is 78 kg.

Is this phenomena that I am talking about the same as being overpowered? In Norway, it is called "being screwed", as the sail wants to do a screw motion.

i call it backhanding check out my video you will see it a lot while am getting on to the plane and then settles once i am going properly this was a very gusty day winds from 18knts to 28knts

you will notice my front hand goes forward when big gust hit

Backhanding is common on the modern no cam sails. The North e_type used to come with a sticker above the clew holes noting that they required more outhaul tension than regular sails. I found that 1 or 2cm more outhaul always fixed the backhanding.

Decreasing downhaul would have the same effect because it tightens the outhaul. However, you probably don't want more power in your sail when this is happening so I'd leave the downhaul alone.

I think it's cause by the luff inflating in the gust beyond the designed tolerance. Tightening the outhaul keeps that movement in check.

Capie! I recognize you as a famous e_type fan. Have you experienced backhanding on e_type?

I also think it was you who introduced me to the term luff collapse; I have never looked up on the sail while windsurfing, so I do not know the state of the luff while the sail screws during the gusts. Can it be that I am experiencing luff collapse?

Im by far not an expert but I think Grich62 has a point. When this happens to me, or when loosing speed (which is when I usually fight most with gusts), moving my front hand forward usually solves the problem for me. Strapping in early is definitely a must to get comfortable, allows me to have a better grip when a strong gust hits me and also having my weight towards the back of the bord seems to counterreact the effect of a gust more. I am a very lightweight, 63kg and I sail a 6.5m normally... I have 2 boards, my 125L seems to jerk more with big gusts, but my 85L is so easy in stronger winds... I guess there is so much science behind sailing.

Select to expand quote

waytata said..
Im by far not an expert but I think Grich62 has a point. When this happens to me, or when loosing speed (which is when I usually fight most with gusts), moving my front hand forward usually solves the problem for me. Strapping in early is definitely a must to get comfortable, allows me to have a better grip when a strong gust hits me and also having my weight towards the back of the bord seems to counterreact the effect of a gust more. I am a very lightweight, 63kg and I sail a 6.5m normally... I have 2 boards, my 125L seems to jerk more with big gusts, but my 85L is so easy in stronger winds... I guess there is so much science behind sailing.

Interesting.. when I'm survival sailing I have my front hand further forward closer to the mast so I can push away in the gusts and a wide grip..maybe that's why..?
I also do it when I'm a bit scared..