Open source 12-15m high performance/semi-cruising catamaran design

Discussion in 'Multihulls' started by groper, May 10, 2017.

  1. UpOnStands
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    UpOnStands Senior Member

    Interesting, SIG45 runs the anchor off the longeron. Probably the anchor is the smallest aluminum one available.
    This shows the conventional solution to bow bury, make the bow really high and keep the decks flat. Certainly is simpler than trying to locally reduce the freeboard a'la Fujin.
    What's your vision of the bow/fore deck shape?
     
  2. groper
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    groper Senior Member

    Flat deck to stem;
     
  3. UpOnStands
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    UpOnStands Senior Member

    this is from TS50 XL
    The bow does have a cleat, looks like sufficient foredeck to actually use it. SIG45 has no such space or cleat?
    PS; check out the video at 3:20 - 3:26 does not look like a comfortable steering position/ arrangement :p
     

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    Last edited: Jun 22, 2017
  4. groper
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    groper Senior Member

    Ok im happy with the stiffening arrangment now, unsupported spans no more than 1200mm on the BD floor. This image shows the general arrangment of all beams and structural items from the underside perspective. As a bonus, the stiffening channel sections can be used to rout the jib sheet ropes from the aft beam turning block, under the BD floor to each end of the self tacking jib sheet track which will run across between daggerboard and mast step.
    And this from above - this time with the roof which is 18 square meters in area.

    I split the prodder into 2 beams so i can drop a ramp down through the middle of them and have access to the water (and the beach) that way using the spinnaker halyard to raise it and lock it up with pins or similar.

    UOS - generally with respect to being on the helm - when cruising, 99% of the time the boat is on auto pilot so im not concerned with being out in the sun etc. When racing, this position is best as you can see the sails and everything you need to and all sheets are right there in front of you as per sig45 layout.
     
  5. UpOnStands
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    UpOnStands Senior Member

    Groper, the position is fair but my point was that the helmsman was unable to brace his feet and it looks as if the rudders need considerable force at times. Either the chair should be adjustable in height or a foot brace is needed?
    Looking better, hulls are still developable?
    If you take the roof option would you still keep the aft entry or switch to side door?
    With roof looks like a serious contender to the SIG60. Heave reduction etc.
     
  6. groper
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    groper Senior Member

    it will be like so;
    [​IMG]
     
  7. UpOnStands
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    UpOnStands Senior Member

    looks like the experts don't do instruments or engine controls :D
    racing 99%
     
  8. waikikin
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    waikikin Senior Member

    Maybe you can still have the aft beam pushed right back but with simple pivoting davits- have the tender outside when you want it there & swing inside if berth space an issue, if the davits drop into tubes like a laser mast step in the aft beam you can unship the dinghy & davits when you like, you might even have the "platform" lift/cradle available as well as options but not complicating the main build. Seems a shame to waste easy extra deck space that only costs the little resin/glass/foam/form to create. It's a biggish boat so the "bigger" you can make it for the same effort looks like good value.
    Jeff.
     
  9. groper
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    groper Senior Member

    You sure about that?

    [​IMG]
     
  10. groper
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    groper Senior Member

    The problem with any performance oriented boat is a reduction in accommodation space or any other space. Having the rear beam that far back simply increases the required section sizes of the beams and stiffeners to keep deflection equal. So you end using more material to achieve more space and weight and cost increases with it.
    The whol idea behind the hull design is having enough space down below - its quite a voluminous hull. The bridgedeck becomes an outdoor living space and theres a mixture of sun amd shade areas. This is basically a 40ft size boat with 50ft length hulls and thats deliberate to keep costs down and not building more boat than one needs. As it is, there is a huge outdoor living space, does one really need more?
     
  11. UpOnStands
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    UpOnStands Senior Member

    OK, tender on aft davits, not a problem, swing or fixed is not so important, Moving that aft beam fwd is a key design choice. Another fixed point. Good.
    Helps to position the traveler and provides some space flexibility for aft steps to swim step?
     
  12. UpOnStands
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    UpOnStands Senior Member

  13. groper
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    groper Senior Member

    Yep :) also shows the sandwich panel made with 4mm ply skins works a treat too. I have already decided to use ply sandwich panels for the interior flooring and bunk tops etc.
    The bulkheads i have a better idea...
    In fact, if this comes together as planned, no interior painting will be required at all...
    I did some plate exporting last night, all is well, all the bulkhead landings and other intersections exported with it so these can be setup on the flat panels during infusion. This is what the developed inner topsides looks like. weired huh? after its bent into the nice curve it should be, all these intersections will be plumb and level.
     
    Last edited: Jun 23, 2017
  14. UpOnStands
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    UpOnStands Senior Member

    Looking good as it should
    Any value in making skin offsets at the main horizontal seams to aid in assembly. Top panel has 5mm external skin lip (extends beyond the core), bottom panel as 5 mm internal lip. umm, Might make the panels too difficult to handle.
     

  15. groper
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    groper Senior Member

    Another useful tool - i input the relevant formulas into a spread sheet so you can calculate sandwich panel properties, or (composite beam properties) as per the hexcel sandwich panel design theory formulas. Its still a WIP, but this is what i have so far;
     

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