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post #11 of 35 Old 06-07-2013 Thread Starter
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Re: main sail blown?

I'm in Alameda marina, by Svendsen.

I'll try to set up a vang. I had my standing rigging replaced recently and the yard tuned it. Maybe it needs some retuning. My front lower are very tight but my back lower are more loose, I think it's by design because the riggers set it up this way originally. although with the shape of my mast, I doubt it will arc much even in high wind.

Really, from my recollection of the last day, I really feel like only tension on the boom might make the sail flat. I think this is way beyond a small tuning of the mast.


I'll try to take a pic next time.
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post #12 of 35 Old 06-07-2013
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Re: main sail blown?

I would define a "blown" main sail as one who's belly is deeper than 15% of the measured foot of the sail. A 15 ft boom length should only result in a belly 2 ft deep. If the belly is deeper, you would benefit by a newer main sail. However, I believe if you have lee stays drooping, you need to tune your rig. The weather helm is because of poor rig tuning and not because of your main sail.

Rule of thumb is extreme weather helm =your forestay is way too loose. You could tighten it and see if that fixes it....Although in tuning a rig this is not the first control you start with. Have a look at the Selden tuning guide and do it right.

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post #13 of 35 Old 06-08-2013 Thread Starter
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Re: main sail blown?

They are not that droopy, just not that much tensioned. I looked at some of my neighbors' boat in the marina and their halyards are in the same order of tension, sometimes tighter sometimes less. I go windsurfing once in a while. Essentially whe you use your sail your take the job of the shrouds to control the sail. the position controls the direction of the force (equivalent to weather helm, or lee helm) but not the shape of the sail, at least not noticeably. I understand the sail is of a different nature, rigid with full battens but even if were dacron (and it is on the trainer sails) the shape is not set by the position.

So maybe my weather helm is accentuated by my shrouds but i think the shape of the sail itself and the large curve on my leech is either the boom kicking up or the sail that is baggy. Tomorrow I'll work on setting up a boom vang. I think I'll add a g10 pad on each side of the mast to reduce the compression load. I cannot put a compression tube inside without taking down the mast unless I'm mistaken on the operation.
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post #14 of 35 Old 06-08-2013
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Re: main sail blown?

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Originally Posted by flo617 View Post
.... I think this is way beyond a small tuning of the mast.
It may indeed be beyond a 'small tuning' but it could be that the mast needs to be moved forward enough to get the CE ahead of where it is now enough to ease the helm. Less rake, if you have any now.

A flatter mainsail shape will help too, and setting outhaul and vanging down will help some of that if the sail's not in fact beyond useful life.. and it's easy to try first.

Ron

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post #15 of 35 Old 06-08-2013
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Re: main sail blown?

the way the blown out sail effects the weather helm is that the draft , max cord of the airfoil has moved back. which does the same thing as moving the mast head back , more aft rake. the center of lift of the airfoil moves back causing weather helm, the same as leaning the wind surfer sail back when you tack to make the bow turn into the wind. look at the sail when close hauled , if the max cord, max belly, of the sail is futher back then about 30% of the cord length then the sail is done. the amount of belly is not as important as where the belly is on the sail.

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post #16 of 35 Old 06-08-2013
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Re: main sail blown?

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They are not that droopy, just not that much tensioned. ...
Excuse me, but this isn't a debate. Frankly how would you know? How many boats have you tuned and how many sailing rigs have you done?

You come on here with an issue, and people are trying to tell you what to try first. If you thought you had all the answers, why are you here asking questions?

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post #17 of 35 Old 06-08-2013 Thread Starter
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Re: main sail blown?

I'm sorry, I didn't mean for anyone to feel insulted. I'm just providing feedback and short of a picture which I do not have, I can only give my gut feelings as feedback after feeling the tension on my shroud and recollecting the shape of the sail and why it felt like this at that time.

I am a critical person and I tend to think negatively so my first reflex is to question all opinions, mines first. I guess this is what I have to do everyday in my engineering job and that tends to carry here too. I'm not trying to win an argument or anything like that, I'm grateful for all the suggestions.

Maybe it's just time I try to implement the advices I got and see what works.

Thanks,

Florent
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post #18 of 35 Old 06-08-2013
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Re: main sail blown?

But I'm not insulted. I'm very confused. I've done what you're about to do dozens of times. I've been there...done that and got the "T" shirt.

I've never lost a rig nor have I ever ended up with a poorer performing boat. I tune both monohulls and catamarans. A blown sail can be compensated for with sail controls to some extent. You tighten the halyard as tight as you can get it and do the same on your outhaul. Hundreds of sailors do this every day. Weather helm is usually caused by poor rig tuning and only takes an hour or so to tweak the boat.

I have step by step instructions on tuning a rig on my website but honestly the Selden page is the best tuning guide on the internet.

Engineer or not, try it before discarding the advice.

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post #19 of 35 Old 06-08-2013 Thread Starter
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Re: main sail blown?

I agree. I think I'm a little too lazy (it's hot today) and a little too worried of messing things up. I installed a boom vang today. Maybe I'll go over the rig tension next week.
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post #20 of 35 Old 06-29-2013
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Re: main sail blown?

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Originally Posted by Faster View Post
It's likely that your boom is plenty strong enough for the vang position you're describing, and a vang is a good idea in any case, but primarily for off the wind work. Once your sheeted in hard on the mainsheet, there's little for the vang to do if you're hard on the wind. Unless, of course, it's windy enough that you're into 'vang sheeting' (using vang for luff tension, mainsheet for 'angle of attack' only.. something you might try one day but does require a flattish main to be successful)
Not quite.
The vang while holding the boom down will also thrust it forward against the mast, helping to bend the mast and reduce the draft of the main.
halyard and Cunningham tension will help draw the draft forward on both the main & jib.
Outhaul tension will help flatten the foot and mast bend will flatten the rest of the main. The vang, and, if fractional rigged, backstay can do that.
Prebend can be set in the mast if you have spreaders that are swept back, more tension on the uppers will give more prebend. I know folks who say 'oh the yard set them right when they stepped the mast.' - Wrong - they didn't have a clue. At best, they centered the mast and guess at the rest (unless you have a popular one-design and told them how much pre-bend your sailmaker cut the main for). Racers who know their stuff will set rig tension every time they go out for the day's conditions. But that's a whole different thread, isn't it?

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