20' cedar strip tri

Discussion in 'Multihulls' started by mirlac, Apr 22, 2006.

  1. mirlac
    Joined: Apr 2006
    Posts: 2
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    Location: WA state USA

    mirlac New Member

    It's about 80% complete. a center cockpit high ratio rig sloop. I have problems on placement of the running rigging, traveler etc. The fastening of the rigid box beams crossing the ama between two pairs of bulkheads cause concern because of the stresses involved and interfence with the traveler which should be mounted somehow on top of the aft beam. Short post because this is my first post.

  2. frosh
    Joined: Jan 2005
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    Location: AUSTRALIA

    frosh Senior Member

    Hi Mirlac, I am also about 80% completed on my high AR sloop rigged 18ft 6in tri. I am also thinking a lot about the mounting of the cross beams.
    The easy one is the traveller. The rear beam is an ideal mount, and it can be simply a high strength rope strop with a block running along the strop.
    The stress of the box beam needs to be distributed to as much of the structure of the ama as you can possibly make it. Reinforcement of the skin on the inside of the ama, (both sides, port and starboard ) all the way between the two bulkheads is a good idea. Then reinforce the join between bulkhead and inner skin. Carbon fibre woven and uni-directionals can be used.
    Finally a timber block glued to the reinforced skin with generous surface area becomes the support for the bolts between the beam and the amas.
    I am not an architect or engineer but from boat building experience I am sure that if done well, this is all that you need to do.
    By the way my crossbeams are 100% carbon tubing which will be pushed inside short carbon tubes one size larger.
    My problem is adequately strong mounting of the short tubes without drilling holes through them. :)
  3. mirlac
    Joined: Apr 2006
    Posts: 2
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    Location: WA state USA

    mirlac New Member

    Hello Frosh,

    Thanks for the reply. Right or wrong, I am avoiding the use of carbon fibre. Mostly I lack the knowledge to work with this material. Vacuum bagging, high heat cure, its expense. so contrary the NA's recomendation I used 1/2'' plywood to make 4X7, then tapered, beams. They are 13' 6" log and ridged. I will dismount them whenever I trailer the boat. I have a design I have come up with after listeening to friends, one an eng. and I could share the drawing with you if I knew how to send attachments. My e-mail is my handle plus @comcast.net. I also have photos of the construction. I would like to see what you are doing also.

  4. Doug Lord

    Doug Lord Guest

    20' tri

    Mirlac, how are you coming with the boat?
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