Tension Meter

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Tension Meter

Postby hallcp » Fri Jul 25, 2008 11:26 am

The EC12 manuals make a big deal out of measuring Back Stay Tension (BST) with a little tension meter. Each book includes a plan for this meter. The authors make this measurement the basis for a lot of their advice on sails and rig tuning.

But I rarely see these devices at the lakeside here. Are they really necessary? I'm trying to make one now, but it's a little fiddley to get it to work.

I've searched as best I can and none of the other AMYA classes seem to mention tension meters at all.

What do you guys think?

Charles Hall
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Postby kahle67 » Fri Jul 25, 2008 1:40 pm

Some use them to be able to repeatedly adjust to the same settings from a previous day of sailing so you don't have to fiddle and re-tune all over to find the sweet spot.

I never have used one. Just looking at the amount of mast bend and keeping an eye on headstay sag should be enough.

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Postby Capt. Flak » Fri Jul 25, 2008 3:18 pm

When I first got started, I got one from Mike Zellanack. He makes a very nice one by the way. Anyway, I used it all the time and even kept some notes on tension for different wind speeds. But after time, I learned to sight down the mast for the correct bend and look at the headstay sag and Reichard talks about.

Now I only take it out once in while to check because somebody will ask me what my backstay tension is set to. I'll say, "I don't know, let's see."

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Postby Rick West » Fri Jul 25, 2008 5:15 pm

I consider the tool to be essential is repetitive settings. However, after a while you get to setting it by sight because you have seen it all the time. I use it more in light air and heavy air, not so much in between.

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Postby dr j » Tue Jul 29, 2008 5:14 pm

I use one I bought from Mike Zellanack almost every regatta. First I set by digital meter (my fingers on the jib ;-) ), then verify with the spring thing. It just keeps me consistent and repeatable.

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Postby hallcp » Tue Jul 29, 2008 8:52 pm

Thanks to everyone who responded. I've been reading up on mast bend and jib stay sag, etc. I think I'm beginning to understand more of what's being measured and why.
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Postby greerdr » Sun Aug 03, 2008 5:46 pm

you can also mark the string in the backstay bowsie for a known value.

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Re: Tension Meter

Postby rs vernon » Wed Dec 09, 2015 10:14 am

I claim that some people are fast one day and not so fast another day, and I wonder why. Tension meter does seem to help with the consistency for a lot of us. Experience, tension meter and keeping records of tune on fast easy days. I know they are not readily available, but not too hard to make and calibrate. #6 spring is a good start, if I remember right.

I wrote this up to be a new subject, but it fits in here. Just too many words.

How do you tune BST without a tension meter?

I think one of the most difficult and important settings for an EC-12 is forestay tension. The wind speed is variable during a day and even a race and we have to try to set the backstay tension (BST) so that the jib is happy - proper jib luff sag. Too little jib stay tension and the boat will not point, Too much jib luff sag causes the jib to luff early. Correct jib stay tension gives proper jib luff sag and the boat can have speed and pointing ability. Too much jib stay tension and too little sag causes the jib entry to be too fine and the clue sometimes is that the boat can be difficult to try to sail upwind. It seems like the it is getting hit by a header about every 3 seconds. You tack and same problem on the other tack. But that is a sign of extreme jib stay tension. Slightly too much is harder to detect. Getting it right seems to be based on judgment and experience.

The other tricky part of it is that proper mast bend and main sail shape are a big part of what powers the boat. So you have to do kind of a dance where BST and lower stay tension and position on the stay rack team up to give you proper mast bend and at the same time proper jibstay tension.

You can pretty much see proper mast bend. Set the boat on its side and look down the mast at the main sail shape. Nice deep curve in light air. A little flatter in medium wind, Nice flatness in heavy air. Good

Draft looks to be too far forward? Sometimes right up against the mast? Never good. Too little mast bend and sometimes (above the spreaders) a sign of too much jumpers tension. A channel up against the mast that will not go away can mean that you have stretched the main luff or it can be that Chuck Luscomb can make it go away with meticulous tuning effort.

In high wind, big diagonal creases down low in the main? Too much mast bend down low. (Need check stays or lower lowers pulling aft?) On the typical boat the only answer is to pull aft with tight lowers clipped far back on the stay rack. More BST can be dialed in but only to the point where the lower mast still bends too much. It does help though and also produces more jib stay tension which is good.

How do you tune BST with a tension meter?

You have some of the same obstacles as without a tension meter, but you can keep records of your setup when the boat went fast and easy in different wind regimes and you can duplicate the settings. BST, lower stay tension and placement on the rack, jumper tension. Eventually makes it easier to get it right.

I believe it might not be best to blindly use the JLA/wind speed/BST chart as presented to perfectly set up your boat even if you do know your JLA. It does make it much easier though, and after a while you can figure out whether you want to use the exact JLA horizontal line or go down a line or two to keep from having too much jibstay tension. You do want to paste that chart on the back of your meter.

Comments hopefully?

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Re: Tension Meter

Postby aesch » Sat Nov 26, 2016 12:31 am

Boy, does this hit home! I'm trying to figure out what luff curves to put into some home made sails, and it's a shot in the dark without knowing mast bend and headstay sag.
If you have sails from a competitive sailmaker, he should be telling you what mast bend to carry - this will control your headstay tension and sag. Use whatever backstay tension you need to get the specified mast bend.
My big boat experience has shown that more headstay tension gets you pointing higher - but only to the point that the luff of the jib becomes so flat that the person on the helm no longer has a 'groove' to steer to.
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