Spreader Angle for External Chainplates

Discussion in 'Boat Design' started by Swiftsure33, Nov 14, 2017.

  1. Swiftsure33
    Joined: Oct 2017
    Posts: 9
    Likes: 0, Points: 1
    Location: Tampa

    Swiftsure33 Junior Member

    Hello everyone. In a recent post I talked about restoring the deck on my newly purchased 1960 Rhodes Swiftsure 33. During this process I will be removing the inboard chainplates. They are parallel to the hull, and are thru-bolted to the hull on to a backing plate that is glassed to the interior. Since the backing plates are already set up for this, I'm considering converting to externally mounted chainplates for ease of inspection, avoiding leaks that lead to crevice corrosion and deck rot, and adding strength to the rig. My main concern is that if I move the upper stay chainplates further outboard, this will affect the angle the stay makes to the spreader. The spreaders are aluminum with steel mounting brackets. Is the difference minute enough for it not to be of concern? I realize that ideally I should have a professional rigger take a look, and I will once it comes time to put the rig up, but I'd just like some testimonials from others who've converted to outboard chainplates to see what they did and how it's worked out so far to see what I'm up against. Thanks.
     
  2. Blueknarr
    Joined: Aug 2017
    Posts: 50
    Likes: 2, Points: 8
    Location: Colorado

    Blueknarr Junior Member

    In the late 90s a friend moved his inboard chainstays to outboards. No problem with spreaders.
    However...
    The hull started to crack while we were tensioning the rig.
    The hill's internal aluminum plate was too close to the outside. When chainstay on inside 98% of glass between chainplate and aluminum plate.
    The aluminum plate was rebedded and glassed over. A new SS plate added to the inside. Final bolting thru outside chainstay, glass hull with its internal aluminum plate and new inside plate.

    Vessel headed to South Pacific.
     
  3. gonzo
    Joined: Aug 2002
    Posts: 12,349
    Likes: 198, Points: 63, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    Increasing the angle of the shrouds by moving them outboard will decrease their load, so it won't be a problem.
     

  4. PAR
    Joined: Nov 2003
    Posts: 18,598
    Likes: 377, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Agreed, the distance you'll move the plates is relatively small and you'll gain purchase angle, if ever so slight. Insure the backing can tolerate the loads, as the through fasteners will have a small cantilever on them, so maybe one size up, just to be safe. Also consider epoxy "bonding" these fastener holes, just to insure no leaks and offer a good bearing surface under the fasteners.
     
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