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Old 28-07-2008, 08:31   #1
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rig tuning question!

Before posting this, I have searched and read the different posts on Rig tuning, and the seldon on-line manual, but still have questions!

I have read how to use a 2m ruler, and calipers to set the tension to 3mm (15%) of breaking strength. My 30' deck stepped, mast head rig has 1/4" 1x19 wire rigging, on the shrouds. I guess my main concern is that after "scientifically" measuring the stretch to achieve 15% breaking strength, I then have to sail it, and when I see the leeward shrouds "dancing", then I have to tighten them while underway! This is the case, as both upper and lower shrouds (single spreader) are quite loose at 15-20% heel, beating into the wind.
My main concern is that after measuring to get the proper 15%, I will now be tightening an unmeasured amount to take the half the slack out of the leeward side, and then doing the same on the other side, after tacking, of course! Who knows what the final tension will be?? 20%, 25%, etc!!


The other question is on rake. As my mast is very heavy aluminum, and the 30 year old boat does not have an adjustable backstay, I would not consider the rake nearly as adjustable as on racing type boats. Do i just make sure I have "some" rake and leave it at that?

Thanks in advance!!

PS I was, and still may pay the local rigger to tune it, but if he is not going to do it while sailing / heeling at 20 degrees, I don't see the point. Why pay him to use guage to set the tensions, if I have to tighten them under sail anyway! Maybe he intends to sail as well, but I doubt it for 1 hours labour!
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Old 28-07-2008, 09:15   #2
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I believe you can know the final "tension" by how many additional turns you take to remove the slack. Each thread represents a specific distance and change in tension.. no?
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Old 28-07-2008, 09:33   #3
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Jeff - thanks for the reply. Yes, I guess you could measure the amount of change with one full turn, and then keep track of additional turns.

I guess, in the end, the 1st dockside attempt is just a starting point to get things even, so that additional turns, on each side, will keep everything straight. I diodn't want to end up at something like 40 or 50% of breaking strength though, by taking up an additional 3 or 4 mm on each side.
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Old 28-07-2008, 10:49   #4
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Your hull will definitely distort if the rig is too highly tensioned and you can observe that in "deformations" such as doors not closing and so forth.
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Old 28-07-2008, 11:11   #5
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It's practically impossible to overtension the rig with normal hand tools when stationary, but I would strongly advise you not to tension the leeward shrouds underway when they are slack. There is a huge possibility of overtightening them with disasterous results.
Get yourself a Loos Tension gauge, a Standard Type B or a Pro PT2, and do the job properly.
If the rig is right your leeward shrouds will lose tension but not go slack. If they waggle around they will put a shock load on the wire and rig when you tack and they come up tight.
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Old 28-07-2008, 11:16   #6
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Leeward shrouds which knock around are the ones which fail.
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Old 28-07-2008, 11:20   #7
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Yep, that's definitely the case.
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Old 28-07-2008, 13:40   #8
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As Minnie says, get a Loos gauge. Forget about rulers. Mast rake will affect your balance and pointing ability, the best thing is to find out if you can what was 'factory' for your boat, and what other owners are doing about their rigs.

Get into some boats, like a J/24, and the winning racers are out there changing the tuning AND the mast rake to meet the wind conditions. It doesn't ever get 'set and forget' because no one position suits all conditions best.

By all means ASK the local rigger if he will be setting it static at the dock, or going out with you to show you what needs to be done. I'd guess you'll pay more to go out (or pay less not to) but seeing things hands-on might be worthwhile.
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Old 28-07-2008, 15:12   #9
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"The other question is on rake. As my mast is very heavy aluminum, and the 30 year old boat does not have an adjustable backstay, I would not consider the rake nearly as adjustable as on racing type boats. Do i just make sure I have "some" rake and leave it at that?"

Don't confuse rake with mast bend. Rake is the angle at which the entire mast lines up fore and aft and is not frequently adjusted. Rake is usually aft and the amount can be seen by looking at how far the main halyard stands away from the mast at deck level when allowed to hang free with a weight on it. Rake moves the center of effort foreward or aft, inducing more or less weather helm.
Mast bend is induced by tightening the backstay against the lowers or baby stay. It changes the mainsail shape and is a frequent sail adjustment on racing boats.
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Old 28-07-2008, 17:03   #10
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Different rigs have different specs and features such as masthead, fraction, tapered and the number of spreaders, whether they are athwartship or swept back. Lots of variables here and no simple answer to tuning the rig. However the rigging should be tunned to the proper tension relative to its breaking strength and even that will vary by the type of rigging.

Get a book or get a rigger and a book.
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Old 28-07-2008, 17:20   #11
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Northeaster,

If you do some Googling, you can probably get the rigging tuning specs for your actual boat!
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Old 28-07-2008, 17:50   #12
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"However the rigging should be tunned to the proper tension relative to its breaking strength and even that will vary by the type of rigging."
Assuming any one of the PO's didn't replace a piece of it with something stronger or thicker or thinner and cheaper than original spec.

"It seemed like a good idea at the time."
"But it was the very best of butter!"
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Old 28-07-2008, 18:50   #13
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Thanks for all of the great advice!!

Minnie - Great explanation on rake vs mast bend. No, I was not aware of the difference. I assumed, incorrectly, that the mast started up straight and was bent back, to change the center of effort.

re: the not tightening the shrouds while underway. Too late- just got back from a great afternoon of sailing - winds approx 15-20kts. As mentioned, the shrouds were too loose on last outing (we only stepped the mast a couple weeks ago), so I tightened them just enough to take the slack out, on the leeward side. Also, I did this by adjusting one side a couple of turns, tacking, and then doing the other side - then repeating the entire process. I don't think I would have tightened them enough to be excessive, but will check again next time.

I was quite sure that I read to tighten the slack leeward shrouds underway, in the selden mast on-line manual, or one of the others I found while searching.

Some of the advice her seems to contradict the selden (or other) rig tuning manuals, as they say to set for 15% of breaking strength, but then you still have to go sailing to see if the leeward ones are tight enough!

Anyway, I do appreciate all of the advice. At least they are no longer dancing around, which I think would be worse than a bit overtight. I removed / inspected the chain plates this winter, and used new bolts putting them back in. They are throughbolted through a large fiberglass knee, which is actually part of the hull, so I don't think I have tightened enough to distort the hull, although I realize that it is possible!
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Old 29-07-2008, 04:22   #14
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we were told by the local rigger to go for a sail (after the mast is set up) have the boat fully powered up and then take the slack out, the rig shold NOT be tight while sailing but the stays should not flop around as the stanless will fatigue
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