Mainsail cut

Hi all,

I would like to get some feedback from more experienced F16 sailors about what to do with my future mainsail. At first I'm planning to setup my Blade only for 1up mode, but later when I got hang of that I plan to set it up for two.

This leads to a question that should I order mainsail which is cut to my weight or should I get ready for crew? If I think about this with common sense I can always depower if the sail is fuller but it's hard to get more power if the sail is cut too flat. Problem is that I propably can't depower 2up main as much as I could if the sail was cut directly for my weight, so it'll limit the conditions that I can get out sailing.

So what do you think? What would be best solution for this problem? Is there really that much difference that I should worry about this?

Thanks in advance,
Valtteri

Firstly, I wouldn't worry about it too much. I don't think the cut of the mainsail would ever make the difference between going sailing and not going sailing. It's a question of how fast you'll go when you're out there, and even then the difference is not that much.

Secondly, a compromise between the two can be perfectly effective. I have the standard Ullman sails that came with the Blade, which I assume are a "compromise" cut. I am happier with the performance of the main when sailing 1-up, but at the level we sail at, it's perfectly competitive either way.

Paul

Should the cut of the sail be a little different depending on whether you are primarily sailing upwind unirig or with w jib? Or can you adjust the sail shape with battens so that one mainsail works for both situations?

With modern sail cloths you won't be able to make many changes to the sail shape with your battens

Mary,

The lower halve of the mainsail is somewhat different in draft and twist profile when it is designed to sail with a jib. Or at least that is what you ideally want.

valtteri, is right. It is possible to tune a 2-up mainsail to sail singlehanded well, but not the other way around. In very competitive sailing I suspect that a custom made singlehander sail will be more competitive though.

Personally, I had my mainsail cut to suit my expected 150 kg combined 2-up crew weigth. I use this all the time when I sail singlehanded and it does surprise me how fast it is in that usage. It is a little more work to tune it right but I'm not killed on the course by other boats. I have too little experience with optimized singlehander sails to comments further on those.

But as stated above; I'm quite happy with the decision I took in 2003 to go for a 2-up mainsail and try to tune it down to 1-up usage. I'm using a relatively flexible alu mast, this may help.

Wouter

Compromise sails was something that I was thinking of getting, good to know that there isn't that much difference.

Battens propably plays really big part of sail shape, so hopefully some adjustments could be done with different set of battens if needed. It would be cool to have 1up battens and when changing to 2up battens main shape changes. At least it should be possible, in our current boat we are using different top batten for light winds, so that it's easier to trim.

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Valtteri

I tried the different top battens thing (3 top battens) but I'm not using it anymore. It didn't work as intended on my pentex mainsail. I guess I agree with Scarecrow on this one.

All the stiffer battens did was mess up my batten pockets on my boltrope. I had to repair a few of them because the much increased batten tension had split them apart. In short, the stiffer batten set for singlehanding wasn't a succes by any stretch of the imagination. At least not in my case.

Wouter

I guess that going for stiffer battens that sail was designed for can cause problems, but going for more flexible battens or battens that has different bending characteristic for 2up would be possible. I wont be getting those for now, this was just theoretical speculation if it could be done <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" />

Thanks for your replies, I got the answers that I was looking for.

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Valtteri

About twist and differences in design for uni vs sloop mainsails. To compensate for the "bending" of the airstream created by the jib, one want more twist in the top of a sloop main. However, compare twist in these two pictures from Ullman Sicily, one A-cat and one F-18..



Here are some screenshots of a uni and a sloop mainsail. The differences are not too clear, but visible in the areas outlined.

Ahh Rolf, what you wrote is actually not correct.




Actually to correct for the "bending" of the airstream created by the jib, one want LESS twist in the BOTTOM of a sloop main.

The top is best when it is about the same as for a boat without a jib. Afterall the mainsail top of a sloop rigged rig does not really see any bending by the jib, it is too far above the main body body of the jib.

And that is exactly what I'm seeing in the pictures. The A-cat appears to have more twist low and probably some more draft there as well.

You explained it better than me where the twist is and partly why. But I am still of the opinion that a sloop main need more twist than an uni main. If the uni and sloop was pointing at the same angle, I would also agree that the top of the sail on both boats should be identical.

Funny how disinclined most posters on catsailor.com is to discuss sailtrim and shapes. Especially so when considering that sailshapes and trim is one of the major points for making any boat go fast.

The 2 boats are sailing at different angles so it seems difficult to compare the twists. How are you deciding which has most twist?

In the above pictures, it's not possible to measure and compare twist empirically (Unless you get really fancy by measuring the boom on the F-18 and write a program to remap all surfaces..) But you get an impression of twist distribution and amount. I tought it funny that the F-18 was sailing with what looks like similar twist as the A-cat. But the discussion is about differences in design and flying shape for uni rig mains vs. sloops.

Are these boats sailing in different directions ? It looks to me as if the camera position is the only difference, being directly behind the A Cat windward hull and 4-6 foot (1.2-1.8m) more too windward behind the F18. However, the sail shapes and particularly twist look remarkably similar. It seems to me as if both types of sail plan are getting flatter and flatter to reduce drag.

If one thinks about unified shape of jib and main then the main bending (bag, sag?) should be nearer the mast in 2up sail. In 1up sail there is only main and the curve of main can be spread out more evenly to get more efficient shape making it flatter, because the wing shape is shorter (thus the sag (?) cannot be made as deep, not just because you want lose some power from sail). And in flatter sail pulling the downhaul should have more effect on lower part of sail than with fuller sails.

In Rolf's pictures it seems to me that sails are cut this way, of course A-cat might have used the donwhaul lot more and the F18 might still be looking for more power. It's hard to know differences without being able to pull the strings yourself <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" />

I should have looked the English terms somewhere and I should have written this longer so that I wouldn't look like total idiot, so don't be offended if this post is somewhat confusing <img src="http://www.catsailor.com/forums/images/graemlins/wink.gif" alt="" />

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Valtteri

As I understand it...
Regardless if you 1 or 2 up the amount of twist in the main should be adjustable according to your boat speeds and conditions and your jib should copy that same setting to aviod bad air flow onto the lift aera behind your main. A Sail that can change shape from flat to full is the best cut main but it needs a fully adjustable jib to best compliment watever shape the main sail is set to.
A Flat cut main is easier to change too a fuller main with softened batterns and less tension. Where as a Full main requires Very Stiff battens and lots of tension but you will struggle to flaten the sail completly and will procced to stretch and wear out you sail.