Yeah, basically all the load that pulls against the windward shroud (sail forces and weight of the boat/people) want to make the mast bow out and the diamond wire resists that. Some cats don't bother with diamond wires (hobie 16 for example) and they have to live with the bowing or put stronger (heavier) masts on thier boats. The mast on most Nacra boats is pretty light and tall.
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Dave Bonin
1981 Nacra 5.2 "Lucile"
1986 Nacra 5.7 "Belle"
Winnipeg, Manitoba, Canada
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Replacing my Nacra mast spreader
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Posted: Dec 21, 2009 - 12:20 AM
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Posted: Dec 21, 2009 - 05:18 PM
Here's a diamond wire question thats relevant here. Do you or should you take the pressure off your diamond wires in the off season? -
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Posted: Dec 21, 2009 - 06:12 PM
Thankyou gentlemen, that now makes perfect sense. I had not thought of the mast bowing, I only thought of the mast being tipped to lee, pivoting at the base, hence transferring the load only to the shroud. The hulls, trap etc contributing to bend also makes sense now.
Sometimes the obvious isn't!
I did find the tension directions in the assembly manual.
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Hobie 18 Magnum
Dart 15
Mystere 6.0XL Sold Was a handful solo
Nacra 5.7
Nacra 5.0
Bombardier Invitation (Now officially DEAD)
Various other Dock cluttering WaterCrap
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Posted: Dec 21, 2009 - 06:34 PM
I ran my diamonds at 450 lbs. on the gauge and the spreaders swept to 1.75 inches on my 5.5 SL. This gave me about .5 inch of prebend. This was not a great setting for light air but worked well in 10-15 at a crew weight of about 290 lbs.
That was a class Mylar sail. Not a Dacron like he has on the 5.7.
No way would I go with that much on a dacron sail that was not cut for prebend.
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Ron
Nacra F18
Reservoir Sailing Assn.
Brandon, Mississippi
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Posted: Dec 22, 2009 - 09:41 AM
In the post-1985 manual it talks about tensioning the wires until you are not able to push the diamond wires against the mast 20" above the bottom of the wires but are still able to push the diamond wires against the mast 12" above the bottom. That is the rule of thumb I use.
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Dave Bonin
1981 Nacra 5.2 "Lucile"
1986 Nacra 5.7 "Belle"
Winnipeg, Manitoba, Canada
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Posted: Dec 22, 2009 - 09:48 AM
without getting over technical, and this is much more important for racing and maximizing your speed...
Ron brings up a good point here... diamond tension, sweep of the spreaders and especially pre-bend..are VERY dependant on the cut of your sail.
AS i understand it... the pre-bend should match your luff cut curve (with down/outhaul and some main sheet
edited by: andrewscott, Dec 22, 2009 - 09:49 AM
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