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-   -   Does your rigging have this? (http://www.sailnet.com/forums/gear-maintenance/32901-does-your-rigging-have.html)

superdave 05-25-2007 12:30 PM

Does your rigging have this?
 
I have a stopper on each of my main shrouds that appears to stop at the top side of the spreaders. It looks like it is intended to put more tension on the under-spreader portion of the shroud than on the above-spreader section. I don't know if this is common or not, but I can't find any mention of these in any tuning articles.

My question is, is it true that these are used to put more tension on the lower half? If so, any advice on how these should be tuned?

-Dave

Giulietta 05-25-2007 12:31 PM

send photo, what do you think we are telepathics???

superdave 05-25-2007 12:52 PM

Okay, no photos yet, but I photoshopped a diagram (thought you'd like that, Gui).

The stoppers are pinched onto the shroud itself with two screws; the stopper is then pulled down onto the top of the spreader by tension below. So it seems that I'm supposed to use this to limit some of the upper tension. Does that sound right?

-Dave
http://i211.photobucket.com/albums/b...udstoppers.jpg

Giulietta 05-25-2007 01:12 PM

The only time I saw something like that was in smaller dinghies and it was to stop the spreader from climbing up the shroud when that shroud is detensioned by beeing to leeward.

Pamlicotraveler 05-25-2007 01:19 PM

Dave - compliments to you on your Photoshop skills. You should use them often on here!

superdave 05-25-2007 01:20 PM

Heh... I never knew that could be a problem! Maybe I should try sailing instead of just repairing the boat. :o

So my plan is just to move the stoppers up a bit, tension the shrouds, and drop the stoppers back down and tighten them with a little slack above the spreaders.

Thanks for the help!

-Dave

superdave 05-25-2007 01:27 PM

Quote:

Originally Posted by Pamlicotraveler
Dave - compliments to you on your Photoshop skills. You should use them often on here!

Yeah, thanks. I guess I could defend myself from Gui's wrath if I had to. :D

-Dave

Giulietta 05-25-2007 01:29 PM

Quote:

Originally Posted by superdave
Yeah, thanks. I guess I could defend myself from Gui's wrath if I had to. :D

-Dave

Nahhhh....:D :D :D :D :D

tenuki 05-25-2007 03:43 PM

From an engineering standpoint I would guess they are there to keep the stays from sliding upwards as G described. Stays only 'push out gently' on the shrouds, they generally don't/can't supply the sorts of forces you are thinking about in the directions you are thinking to change the tensioning. Those forces are rather large and I honestly can't think of a way you could change wire tension short of adding more shrouds and attached everything at the spreader. but that would reduce tension on the side you put more wires on, ie the same force would now be spread between the two wires. The question would then be why do that, since you already have shrouds at that point attached near the foot of the spreader. If the spreader was actually able to be strong enough to change the tensions between the upper and lower half of the wire those forces would have to go somewhere. Unfortunately, if the spreader was rigid enough to do that it would act like a giant torque lever and probably bend/break your mast. Spars are not designed to take anything but compressive forces. Look at the way the spreader is attatched to the mast, it looks like you could just bend it down, right, not a lot of up and down strength. But you can push it into the mast directly with a great deal of force, right?

The mast holds largely compressive loads (straight down), the shrouds are under direct tension in the direction of the wire. and the stays have a small compressive load pushing them into the mast. None of the spars can stand much 'sideways' forces but can take tremendous compressive forces, and of course ropes and wires can't stop any sideway force, ie they are pure tension. I'm not at my home computer (photoshop) so i'll have to wait to draw the diagram.

tenuki 05-25-2007 03:54 PM

oh, and the reason it's bad for your spreaders to creep up is that once they get high enough the loads start changing from pure compressive to lateral and will bend that spreader the rest of the way up like a twig for the same reasons I described above. They wouldn't creep up under tension, since a small component of the force under tension pushes them down, but as G said, if they are loose on the lee side they can creep up.


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