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Nacra 5.0 Mast flex question  Bottom

  • Hi all,

    I recently received my new square-top mylar main (and jib) made by Skip Elliott and rigged it up today.

    I have a 4:1 downhaul rigged and noticed when I haul down pretty hard, and without the mainsheet attached, the mast develops a pronounced lateral flex above the mast hound. The flex switches depending on which way the mast is rotated. Old, straight spreader bar if it matters. Plenty of diamond wire tension and the flex is above the diamond wires.

    I never noticed it with my pinhead main but, I wasn't sitting there for half an hour admiring my flashy new purchase, either.

    What does everyone think? Is my mast just a big wet noodle up above the hound or is it about to come crashing down on my head?

    Thanks!

    Jimmy

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    1983 Nacra 5.0 Sail #10
    Dallas, Texas area
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  • It's not going to come crashing down, but the luff of a modern sail on the old style mast spreaders/diamonds will do funky things if its not made for it.

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    Rob
    OKC
    Pile of Nacra parts..
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  • Here she is, without jib! So stoked!

    http://www.thebeachcats.com/gallery2/main.php?g2_view=core.DownloadItem&g2_itemId=102910&g2_serialNumber=6

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    1983 Nacra 5.0 Sail #10
    Dallas, Texas area
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  • yurdleIt's not going to come crashing down, but the luff of a modern sail on the old style mast spreaders/diamonds will do funky things if its not made for it.


    Understood, anything I can or should do about it?
    Downhaul more/less?
    Go to raked spreaders to increase the longitudinal stiffness?
    Hows it gonna react when I sheet in hard?

    Questions!

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    1983 Nacra 5.0 Sail #10
    Dallas, Texas area
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  • I'd ask EP what it's made for first. If you lay on the tramp, looking up, and crank the downhaul, what's it do to the sail shape?

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    Rob
    OKC
    Pile of Nacra parts..
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  • What's it do with your old sail?

    You mention that you didn't have your main sheets connected, so the only force being applied is a vertical downward force via the luff. I can't imagine that force is any different from one sail type to the next. Something has to give, and it's either the luff or the mast which must give. The mast is doing the give by flexing to the side IMHO.

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    Craig
    Windrider Rave Hydrofoil
    Nacra 5.2 Restored and heavily modified
    Nacra 5.2 (one under restoration)
    Nacra 5.7
    Nacra 5.8NA
    SoCal
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  • That isn't going to hurt anything and actually may help you depower. Those mast extrusions can take a lot of bending. In the days before raked spreaders and 12:1 down hauls bending the mast on the minor axis (sideways) was how you reduced the power (in addition to sheeting). The more bend the flatter the sail. With the flat top you can also induce the top to twist off and spill wind. Play with a few settings and you will figue it out. Less down haul for lighter wind days more for heavier. With your current setup you should set it and forget it. You dont want to play with such a light downhaul much on the water

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    Dave Bonin
    1981 Nacra 5.2 "Lucile"
    1986 Nacra 5.7 "Belle"
    Winnipeg, Manitoba, Canada
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