Multihull Structure Thoughts

Discussion in 'Multihulls' started by oldmulti, May 27, 2019.

  1. oldmulti
    Joined: May 2019
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    oldmulti Senior Member

    Wadvogel is a simple catamaran designed by Janbart de Jong in the early 1980’s that had several copies built. The cat is 37.25 x 21 foot that displaces 8000 lbs with a 270 square foot main, 172 square foot furling jib and a 116 staysail in a 7/8 fractional cutter rig. The mast is a 40 foot aluminium tube. The 38 is an extension of a successful home build 33 foot version of a semi wingdeck boat. The hulls are dory shaped and have a length to beam of 12.5:1 at the waterline. The flat bottom hull shape has minimal pounding and pitching if the ends are kept fine according to the designer.

    The cat has basic accommodation for 4 with 1 double berth and 2 singles, a small dinette and galley. There are an additional 2 berth s in the bows if you were sailing in sheltered water. The design can do offshore work.

    The construction is based around the designer’s experience of sailing in shallow water. The flat bottom is 56 mm thick, laminated from 56 x 40 mm batterns. The edges are rounded off to give a better waterflow. The sides are 12 mm ply panels scarfed together. The decks are 10 mm plywood with a layer of 3 mm teak veneer laminated on to reduce maintenance. There are 3 plywood and timber structural box cross beams. Forward 2 plywood and timber beams are used to anchor the forestays. There are Western red cedar covered with glass daggerboards and rudders. The steering rudders are quite shallow but of the limited sailing information I have there are no complaints about steering. The boat in the 80’s was no slower than comparably sized cats.
     

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  2. redreuben
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    redreuben redreuben

    Wadvogel must be Dutch for brick shithouse, thats a heavy duty build.
     
  3. oldmulti
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    oldmulti Senior Member

    redreuben. The amusement is that de Jong's 33 foot version, which had a narrower beam, had a built weight of 300 lbs more than the 38 footer. Yes, these boats are strong.
     
  4. oldmulti
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    oldmulti Senior Member

    The following PI-Craft catalogue contains Arthur Pivers trimaran designs that were relevant in the 60’s and 70’s. I have a lot of structural information about Piver designs but most of the structural design has largely been superseded by more modern build methods for plywood and other materials. As an example, Piver’s cross beams on a lot of his home built tris were done with a lot of plywood and minimal timber. At least 30% of the plies in the plywood were structurally going in the wrong direction and added very little strength with a lot of unnecessary weight. The plywood skins were about the right thickness but a lot of the framing and stringers were either oversized or laying in the wrong orientation for maximum strength with minimum weight. Over the past 50 years many designers have refined plywood wood structures using better plywoods, epoxy glues etc which with better engineering have benefited all of us.

    Please understand we all owe a debt to Pivers experimentation and original designs as they provided the foundation for much of modern multihull development. He truly was one of the pioneers and was excellent at marketing to promote the multihull concept. As you will find later Jim Brown the designer of the Searunner trimarans first built one of the first 24 foot Piver Nuggets before he started serious designing. Of the Piver tri’s I have sailed, the Loadstar 35 foot and Victress 40 foot were the best allrounders. The larger models just had to much accommodation and not enough sail for their size.
     

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  5. Russell Brown
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    Russell Brown Junior Member

    I'll bet there aren't many of you that can say "I remember him".
     
  6. John Perry
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    John Perry Senior Member

    Interesting that the sailplan appears to show inner forestays but the photographs show none, and indeed I would not think it feasible to have innner forestays with a self tacking jib. I wondered how you keep the mast from bowing aft with no spreaders and no inner forestay. Just a suitably strong mast section? But a strong mast section would be heavy, then again, since it is a canting mast perhaps mast weight is less important, or even an advantage.
     
  7. oldmulti
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    oldmulti Senior Member

    The Rudi 6 tri is a home design and build by Arron De Ruiter who was frustrated by the high price of composite production tri’s. He wanted a good daysailer that could carry some camping gear for a few days away if wanted. The tri he designed is a 20 x 13.75 foot weighing 400 lbs and capable of carrying 900 lbs with a Hobie 14 22 foot mast and a 130 square foot mainsail with a 40 square foot jib.

    The main hull is 2 foot wide and is built from 6 mm plywood with timber framing. In the main hull bottom a layer of EPS (blue) foam is glued down with 3 layers of glass over it. This provides buoyancy and replaces stringers. A light layer of glass epoxy covers the hull. The floats are from a Mk 3 Boyer A class cat that has tortured 4 mm plywood hulls. The cross beams are aluminium tubes. Similar boats have 75 mm to 100 mm tubes with 3 mm walls. Water stays provide additional strength.

    A simple effective fun boat. The jpegs show the build and sail plan with an estimate of weight in kilograms.
     

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  8. catsketcher
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    catsketcher Senior Member

    You would have been a very small boy when he disappeared in 1968. Here in Australia it is still pretty common to find people who knew Lock Crowther but he died in 1993. A few around he knew Hedley Nicol but they are getting scare nowadays.
     
  9. Russell Brown
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    Russell Brown Junior Member

    There were two people I remember as early childhood memories and Piver was one of them. Not sure why exactly, if he liked kids or maybe there was a bit of tension between him and my dad. I think he liked kids. The other guy was 7 feet tall and around a lot.
     
  10. oldmulti
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    oldmulti Senior Member

    Attached Files:

    Last edited: Mar 25, 2020 at 3:02 AM
  11. oldmulti
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    oldmulti Senior Member

    Drifter trimarans are designed by Mark Gumprecht, a man who likes light simple boats that can perform well and are cartoppable or trailable. His smaller trimarans are 11.75 x 9.6 foot weighing 100 lbs, a 14 x 10.9 foot weighing 120 lbs and a 15.5 x 11.25 foot tri that weighs 130 lbs. They are light open boats. The rigs on all models are freestanding windsurfer masts with simple sails that roll up around the mast. The sail area varies between 60 to 80 square foot. If you want more performance you could probably use a windsurfer sail.

    All models are built with 3 mm plywood and timber. The timber framing and stringers is not overly complex but is required to built as per plan as the hull skins need the support structure. The hulls are covered by 130 gsm e glass and epoxy. The cross beams on the 12 foot model are 3 layers of 16 mm fir or spruce 100 mm wide. The cross beams flex but are strong enough to handle the bay and river sailing that the boat is designed for. A simple leeboard is used for leeway resistance.

    These are simple fun boats that sail well. Plans are $80 to $100 US available from Duckworks.
     

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  12. trip the light fandango
    Joined: Apr 2018
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    trip the light fandango Senior Member

    I have a love/ hate[Edward Bernaise anyone?] relationship with Americans[present company excluded], the music, the humour, tremolino's, some of the insight into life, the innovations make the relationship worthwhile. We humans are always a bit off at times ,...generalising,cynicism, bigotry etc, included[ha].
    Come to think of it, it may just be humans in general, my shrinking grey matter,, and my personal battle to avoid becoming a grumpy old man.
    Jim Browns recollections particularly the one[so far] about his friend explaining why blokes do things like build/sail boats struck a chord. I have seen 'the case for the cruising multihull' many times on ebay as it's often the only trimaran offering. I'm enjoying Jim's writing style so my tiny budget will have to give a bit,.. thanks old multi..
     
    Last edited: Mar 29, 2020 at 6:36 PM
  13. oldmulti
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    oldmulti Senior Member

    TTLF. Dont buy "The case for the cruising trimaran" just yet,wait until the weekend, I have a source for the PDF available.
     
  14. oldmulti
    Joined: May 2019
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    Location: australia

    oldmulti Senior Member


  15. trip the light fandango
    Joined: Apr 2018
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    Location: Rhyll Phillip Island Victoria Australia

    trip the light fandango Senior Member

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