Formula Sails

techno900 · Joined: 28 Mar 2001 Posts: 4161

westadamsvets said:

scottybda · Joined: 04 Sep 2012 Posts: 67

I think it's less about tighter leach vs looser leach and more about the optimal amount of twist and point of sail. I was racing recently in the UK in an event using Kona boards. They are quite different in their downhaul requirements so difficult to accept when you come from a regular board background.

I think because the boards are heavier and more draggy they need less twist to grunt the boards along. Anyways I was told by Mr Larson to ease off the downhaul more, but I always kept a smidge more than the others in the fleet. We are not allowed to pump on the boards, but what I did notice is on the 3rd day we briefly got enough wind to semi plane. On the triangle reaching legs I managed to will my board past everyone to the front of the fleet.

On the fourth day we finally got some planning winds (and slalom) and again with a bit more twist than the average our tractrac GPS units had myself with the highest top speed by about 2 knots apparently. On the last heat I had let off the downhaul to power up the sail, but felt draggy with way more side pressure.

They figured out back in the late 80's twist is good. As you start to accelerate the angle of the apparent wind changes as you move up the sail due to surface friction over the water. The wind higher up is relatively faster so the angle of attack for the sail needs to be shallower to avoid stalling the sail.

So if you are trying to plane, not enough twist will stall out the tip of the sail as you accelerate, too much and it never sheets in enough to gain the power. I think this applies also when pumping, so finding the happy medium is important. When you let off the downhaul the sail gets fuller by default, that also provides the grunt to plane.

I think it's all quite complex and more to do with rigging right for the given windspeed and conditions. If you are struggling to pump a sail onto the plane, probably the wrong size or tuned wrong.

I use a North XTR and was out the other day well powered on my 6.2 RSR, I put on 2 more clicks on the downhaul as I felt a smidge on the limit, but felt fast. I for sure lost a bit of get up and go, but also the board speed was a bit less also. If the wind came up another few knots probably would have been good, but for that wind speed, less leach twist worked better for get up and go and also board speed.

I don't think there are absolutes, I do find with the XTR I get a good feel for sail settings as I can adjust and do adjust quite often. I'd say for a planning board you'll always want a degree of twist, but as far as the optimal that's down to so many variables it's up to the sailor to experiment and find what works for them.

konajoe · Joined: 28 Feb 2010 Posts: 517

Re: Last post.

Don't confuse twist with a floppy leech. It's impossible to rig a Kona sail with no twist. You can eliminate any floppiness in the leech, but the sail will always have twist.

You didn't throw in a few pumps to get planing before others, did you? Kona sails pump better with a tighter leech. They'll pump onto a plane earlier with a tighter leech, but the top end planing speed will be lower. That's the rumor, anyway. Pumping isn't allowed.

I started a new thread on sail twist.

scottybda · Joined: 04 Sep 2012 Posts: 67

We were not allowed to pump and think everyone was good about that. I just maybe hung off the boom better? Cool

To me the rigging didn't seem to have twist, I had it twisting till the 1st and a bit batten and was told it was too much!

Got to admit looking at other rigs had me confused as they looked even less twisted than me statically.

To me when the rig doesn't have proper twist the tip hook back in rather than breathing out. If you look at my rig (0:45 seconds) you can see it hooking. That was on the third heat for the day when I let off the downhaul, but then the wind came back up to about 18 knots and ended up silly overpowered! Kept cussing myself for letting it off!

https://www.youtube.com/watch?v=ShC3eUHWXA4

konajoe · Joined: 28 Feb 2010 Posts: 517

The leech closing at the tip on Kona sails is a sign of too much downhaul. http://www.konaone.com/learn-to-windsurf/guides/tuning/ So, you were doing well due to skill and determination.

I've sailed Kona with Tim a few times, and David once. Good guys!

Did they make you sail reach races in planing conditions instead of triangles? I hope they never do that at a race I go to. The upwind/downwind legs are so tactical when it blows.

rangerider · Joined: 19 Jul 2009 Posts: 206

Follow-up on my original post: I sailed my 12M 2014 Avanti Machine FW sail for the first time yesterday. Isthmus had it on close-out with the matching mast and I am interested in that sail technology so I sprang for it. I rigged it in my back yard days ago and it only took me about 2 hours and 3 tries to get it rigged reasonably well. I am still having problems with cam rotation and I have played with downhaul / outhaul / and adjustable shims for the cams so it is not quite where I need it as far as tuning.

The sail is huge, it makes my 9.5 feel small and playful. It planes SLIGHTLY earlier than the 9.5 and stays on plane through lulls better. It goes upwind better and faster. It gives very smooth power delivery - maybe too smooth in that I never got the sense of acceleration that I do with other sails but it builds up to a high speed easily, my family insists that they had never seen me going so fast which surprised me (not GPS accuracy I realize). It is not intimidating but it is a bit more tiring to handle and it handles slowly. It really feels like I am sailing a boat more than windsurfing. I'm not disappointed with the purchase but for sure it wouldn't be for everyone. I think I will get more out of the setup with a bigger fin so that is next. Thanks again for earlier input.

techno900 · Joined: 28 Mar 2001 Posts: 4161

Large formula sails have always had rotation problems, but some brands have done better at resolving them. The bigger the sail, the lighter the wind, which means that to pop cams, it's more difficult in lighter winds and easier with stronger winds (smaller race sails).

Punching or kicking cams is not unusual to get rotation in light winds.

As far as how to improve rotation on your sail, I don't know, but doing some web surfing looking for the answer will likely help.

jingebritsen · Joined: 21 Aug 2002 Posts: 3371

counter intuitive with double luff sails. provided the cams are seated correctly, and shimmed to fit the mast, typically more down haul tension makes for better rotation. having wind enough helps lots too.

rangerider · Joined: 19 Jul 2009 Posts: 206

Thank you both. Yes - there has been punching and kicking. I have watched some formula and slalom sailing videos with the sailors giving a hard pull or pump against the wind on the new side to complete the rotation which has not worked. I messed with shims yesterday and today I'm going to add 2 cm extension and increase downhaul to try to get better rotation of the cams above and below the boom which is where the problem lies. I think the cam just above the boom is the sticking point. If I can't get it sorted on my own I will work with Isthmus to get it figured out. As an aside I can imagine if I am the retailer not wanting to sell race sails to recreational sailors like myself - I hope to resolve the issue without wasting too much of their time.