Blocks to Carbon Spar

Discussion in 'Boat Design' started by BobBill, Sep 16, 2015.

  1. BobBill
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    BobBill Senior Member

    Attaching Blocks to Carbon Spar

    I have a 26-foot long carbon yard (that vertical spar is yard technically) and boom. (See schematic for visual). The upper 16-feet of yard is carbon and near all of the 16-foot boom. I do not want to harm the integrity of the carbon by drilling etc, and wish to keep as portable, with no repeated orientations.

    I designed the goose neck so the yard and boom can be hung as found, meaning no fixed orientation.

    Blocks must be attached to yard to raise and lower it and are needed for sheets on boom...like any other boat...and hung by straps or looped line, that allow for 360 degree rotation (see pic of looped line.)

    The idea, especially on the boom, when raised to vertical, is to keep the straps/line holding the blocks etc in place...I should add that the areas along the carbon at attachment points have glass wrap to limit wear and separate materials that might create problem...

    At this point I plan to use either polyester line (1/4-3/8") or wood furnace glass insulation (round, low cost, and compatible) to wrap around the spar on each side of the strap to keep the strap from migrating along the spar in use...

    Tricky, since the round shape of the material on each side means stacking it with some compression to form the needed barriers...

    I had planned to use two-side-by-side poly line (even stove gasket-all glass) wraps as base and add a third in the "groove" formed by the two--on each side of say the looped line in the illustration shown to help visualize. Line like Dyneema or a nylon strap etc, seems practical means to hang the blocks between these barriers.

    Then there is the consideration of using peel-ply as well to position and so on.

    I understand there are various bights, loops and knots that can be used with most lines to hang blocks.

    With the many carbon spars in use today, not much on the I-net, so wondering if any thoughts here on this approach.
     

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    Last edited: Sep 16, 2015
  2. messabout
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    messabout Senior Member

    Common practice for Sunfish halyard to yard connection is to use a series of half hitches, about four of them. It works with dyneema and other good quality line, just fine. For added assurance for non slip you can use a couple of rounds of duct tape on each side of the hitches, or on top of the hitches if you don't mind that the line will get sticky.

    If attaching a block, leave some line hanging out of the begin end of the hitches, tie a bowline in the loose ends to capture the block,...... or take a few hitches capture the block and go back up to the spar and finish with a few more hitches. Tape the hitches down with duct tape and the block will stay where you told it to stay. If you want to keep the bale end of the block from banging against that nice CF, stuff a piece of Ensolite foam or similar into the loop that holds the block.
     
  3. Stumble
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    Stumble Senior Member

    Take a look at pictures of A-Class catamaran booms. They are often made from broken masts and have the same issue. Generally dyneema strops for everything in the middle of the boom, and a through deck block for the out haul.
     
  4. BobBill
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    BobBill Senior Member

    Stumble, appreciate the heads-up...I had looked at A Class Cat pics and this time did a "A Class catamaran boom" search and ran into this http://carbonicboats.blogspot.com/2010/07/mid-boom-sheeting.html

    and still looking...good stuff, for unsophisticated me. Might be the ticket.

    Glad I put off the job to see what came up here. Thanks.
     
  5. Stumble
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    Stumble Senior Member

    Ha their booms are pretty nice. Most of us are using old broken mast sections however. They are pretty proud of their work.
     
  6. BobBill
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    BobBill Senior Member

    Yes, Stumble, it is so...and they do complete some excellent work.

    I too am using busted windsurfer carbons, split bottoms, which I saw off and sleeve the things. I was lucky and picked up four of them for not much money, including the cases, which really are not much use when assembled spars are finished as too long.

    But, I will say this the things work just fine and I guessed on how stiff with sleeves. The first one I used carbon sleeve and that wee boat sails like it was designed to use the carbon instead of wood.
     
  7. Stumble
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    Stumble Senior Member

    All boats were designed to use carbon instead of wood... They just may not know it yet.

    It's amazing how different a boat feels dropping just a few pounds out of the rig.
     

  8. BobBill
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    BobBill Senior Member

    Interesting comment, Stumble.

    My Kite Class dinghy with orig Stika mast (bolt rope) and wood boom were about same weight as the carbon mast less 2 lbs, but I used a metal mast base and a handy Force 5 boom which worked perfectly on boat. Thing is, the reduction of high weight was noticeable and now the boat can use new or original rigs...

    I wish carbon was less expensive and did not need to be insulated from certain materials, but what the heck...works.
     
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