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Old 06-10-2008, 14:06   #1
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Do my shrouds have too little tension?

Started thinking that my shrouds may have too little tension a couple of weeks back and while sailing last weekend checked out the leeward shrouds while the rigging was powered up (full sail, 10-15knts breeze).

Sure enough there was a couple of inches of looseness.

Is this normal?

Edit:
This thread here seems to have some merit on tuning without pressure gauges (I also read the another thread on this forum on how to tune to 15% breaking strength by measuring stretch).
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Old 06-10-2008, 16:32   #2
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It isn't the looseness or tightness of the shrouds that really matters. It is how straight is the mast. In those conditions if you look up the mast, is it straight and does the mast head not fall off to leeward? Looking fore and aft, is the mast straight or curved back -- not an s-curve?

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Old 06-10-2008, 16:33   #3
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Yes I was taught ( 30 years ago ) when glass boats started , that you cannot tune right after being launched,( hull needs to settle ) and when you tune make sure the stick is straight up upper and lower spreaders level or up 3-4 degrees according to specs then mark or measure lower turnbuckles then go sailing ,after each tack take up a couple or three turn on leward, till you only get a little slack on leeward return to dock ' and feel the rigging I do it on up to 65 foot boats with a line and my arms held level . if you are doubt about upper and lower shrouds you can take a mirror and sight up the sail trak this is best done before boom and sails are on Ole
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Old 06-10-2008, 17:01   #4
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Actauly, the tension in the shourds is VERY important. They have to be "pre-loaded" in order to avoid shock-loading the system. It is also vital to have the mast straight, but to say that the tension is is "not what matters" is a very serious mis-statement. A mast can be straight with slack shourds, and that would be very bad.

You ceratinly can measure the tension in a wire by measureing stretch. It basically the same way the "tension gauges" work.

If you are going to tune your own rig, get a good book on the subject that covers it in detail. For a complete treatment, you could get "The Rigger's Apprentice" by Brion Toss or Sail and Rig Tuning by Ivar Dedekam for a less formal, but very good and clear treatment.

Basically, the approach is a two step one. At the dock, you adjust the tension in the shourds to the proper level, and adjust lengths so the mast is straight from side to side, and has whatever rake and curve is appropriate for the rig design.

Then you go sailling, and fine tune the lengths of the shourds and stays.

In 10 to 15 knots of wind there should NOT be "several inches" of slack in the rig.
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Old 06-10-2008, 18:27   #5
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Borrow or buy a loos guage.

Slack the uppers and lowers

Measure equal distances from the stem fitting to a point abeam the mast. Use the Main halyard to measure the centering of the mast. Adjust the uppers to center the mast.

If you expect heavy airs tension the uppers to the higher end of the recommended range. If you expect light airs tension to the lower end of the range.

Recheck the centering

Sight up the mast and look for the bulge in the middle.

Adjust the lowers to take the bulge out.

If you expect heavy airs adjust the lowers to the higher end of the scale. If you expect light airs adjust to the lower end of the recommended range.

Recheck the uppers tension. It will have dropped a point or 2.

Recheck the center.

You may consider adjusting the backstay to get zero tension on the forestay.
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Old 06-10-2008, 19:51   #6
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Ditto on what GreatKetch says And....

there are several factors involved.
If the rig is tensioned properly at rest and the lee shroud slacks in a 15 kt breeze then you have a hull or sail problem. How far is the boat heeled?

The deck could be bulging (around the mast) allowing the chainplates to come together causing the slackness. If you have a deck stepped mast this will be unlikely or less evident. I've read that it's common on multi's though, due to hull flex.

If the chainplates are creeping this could be a major problem. with smaller boats this is common. The hull is very flexible and the shrouds are usually only attached to the deck.

If you are heeling over with a lee shroud flopping and the jib sheet happen to snap, that flopping shroud would take a shock load that could be disastrous..
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Old 06-10-2008, 20:57   #7
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Thanks for all the feedback.

Maybe a couple of inches is an exaggeration - but loose they were and more than felt healthy hence this thread. I am worried that the slackness is a new thing, but it might also be something that just became more apparent to me as the boat has become more familiar. Am really hoping the latter...

I'd say they feel too slack at rest, one notch less on the slackness scale and they'd be described as loose. This gives me hope.

The mast is deck mounted (and the deck feels solid and looks straight, no soft core, no cracks in the gelcoat). The shrouds each have an external chainplates that is perhaps 18" long (not at boat so guessimating here), 3 on each side. After what delmarrey says I'm going to take a closer look at this area including the inner bulkheads nearby.

We've might have sailed the boat as much this year as it was sailed in the previous few years as the POs were from out of state. We've also definately had the rail down pretty hard on occasion (memories of the Admiral hanging onto the dodger with a certain look in her face spring to mind - bless her socks she still goes out with me), though not this last sail (perhaps 25deg heel close hauled in maybe 15knts).

Guess I'll hit one of those books mentioned and start looking into my next learning experience before the winter winds get this far south! "Rig Tuning by Ivar Dedekam for a less formal, but very good and clear treatment" sounds like a good recommendation. Hopefully I don't need rocket science here but a stick that remains pointing the right way!
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