Cat Hull Design

Discussion in 'Multihulls' started by Slimes, Mar 18, 2024.

  1. Slimes
    Joined: Mar 2024
    Posts: 4
    Likes: 1, Points: 3
    Location: Townsville, QLD

    Slimes New Member

    Hey guys,
    Long time lurker, first time poster.
    Just wondering if anyone has any thoughts of concerns on this hull design Im about to crack into building.
    A little bit of background... this is will be a simple ply and epoxy build designed as a coastal camp cruiser for the coral sea of the coast of north queensland, australia (potential the whole eastern coast).
    Had to be a simple to build, shallow boat with nothing too fancy.
    A lot of inspiration has come from things like the wharram cats, the work of the berque twins (micromegas 3 and 5) and the work of Harryproa. Not looking for a flash or a fast boat. Just a simple coastal cat for fishing and camping trips.
    Will be about 6m long overall, all mostly symmetrical and bulkheads are upside down 'house shapes' with a shallow v bottom and vertical sides. Bottom and side panels are 600mm and the beam width of each hull is 1000mm.
    Just looking to find out if anyone can see any glaring mistakes or has any comment. Showed it off to some local guys and everyone seems to think it'll go ok, thought I would turn it over to the greatest source of boat knowledge I know of :)
    20240316_203604.jpg 20240316_213716.jpg 20240316_220452.jpg 20240316_220459.jpg
    Thanks in advance for any interest or comments.
     
  2. C. Dog
    Joined: May 2022
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    Location: Coffs Harbour NSW Australia

    C. Dog Senior Member

    Maybe consider reducing beam? I'm looking at a small coastal fishing, day sailing sort of rig, mostly for getting a dose of salt in northern NSW, and I keep coming back to Gary Dierking's boats because they tick a lot of my boxes. We have had a small storm front, circling not far out to sea for days now, keeping most local boats tied up or ashore; generally May weather that one.
     
  3. Slimes
    Joined: Mar 2024
    Posts: 4
    Likes: 1, Points: 3
    Location: Townsville, QLD

    Slimes New Member

    Cheers C.dog, Yeah definitely the one piece of advice that keeps coming back to me. Ive been stubborn but I think you (and everyone else) are right. The whole thing was sort of designed around ply sheet dimensions for minimum wastage. Seems to me like I should either scale up the length from 3 sheets long to 4 (making it closer to 8m) or scale down the beam to 600mm same as the bottom panels. The reasoning behind the 1m width was to have a little interior berth for super rainy days trapped in a bay. My wife and I are NOT particularly big people (hobbit jokes abound). It would be no great loss to lose the width really.
     
    C. Dog likes this.
  4. C. Dog
    Joined: May 2022
    Posts: 307
    Likes: 105, Points: 43
    Location: Coffs Harbour NSW Australia

    C. Dog Senior Member

    Mate surely the V bottom is eating ply? If you go narrower, a flat bottom will be barely noticeable and maybe deck the top and have a swag rather than use the hulls for accomodation? You will work it out.
     
  5. Slimes
    Joined: Mar 2024
    Posts: 4
    Likes: 1, Points: 3
    Location: Townsville, QLD

    Slimes New Member

    Definitely going to deck the tops... the original design actually had flat bottoms like micromegas 5 and the harryproa designs. Looks like I've overcooked it as usual haha. Thanks for the advice :) Much appreciated.
     
  6. fallguy
    Joined: Dec 2016
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    Location: usa

    fallguy Boat Builder

    propulsion?
     
  7. Slimes
    Joined: Mar 2024
    Posts: 4
    Likes: 1, Points: 3
    Location: Townsville, QLD

    Slimes New Member

    Sail. Tossing up between gaff or junk.
     
  8. C. Dog
    Joined: May 2022
    Posts: 307
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    Location: Coffs Harbour NSW Australia

    C. Dog Senior Member

    That's a reason why forums like this are so valuable, we can get locked into a mode of thinking where a particular solution becomes the only one. Peer review jolts us out of that and back into the realm of free thinking. I dare say a viable solution will rise to the surface shortly. One suggestion, it is often recommended on here that the designer/builder start with somebody else's proven plans before they graduate to building from their own design, and I can see positives in that for a budding Wharram or Bolger, for example.
     
  9. bajansailor
    Joined: Oct 2007
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    Location: Barbados

    bajansailor Marine Surveyor

    @Slimes have you calculated the buoyancy available in the hulls at the estimated load waterline - and have you also tallied up a weight estimate of all the bits and pieces that go into the construction of the boat (incl the sailing rig), along with an estimate for the weight of the two hobbits sailing her, and their personal gear and stores?
    In an ideal world the buoyancy available would be approx equal to everything in your weight estimate - but you might well find that it is not....... :)
     
    BlueBell likes this.
  10. fallguy
    Joined: Dec 2016
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    Location: usa

    fallguy Boat Builder

    For the cost of proven plans; not worth the failure potential to design your own. Too many variables, displacement vs weight, proven daggers/rudders/sails, beam attachments, not to mention hull shapes..

    Use your model as a starting point to review other's plans. I won't endorse all of them, but Woods has some good designs.
     
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  11. BlueBell
    Joined: May 2017
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    Location: Victoria BC Canada

    BlueBell . . . _ _ _ . . . _ _ _

    Build to a proven design that meets your needs (SOR).

    OR

    If you're young and full of piss-and-vinegar, at least compare your design to other proven designs similar to it.
    Know that the chance you will be disappointed with the outcome of your first design is higher than you think.

    Cheers
     
  12. rberrey
    Joined: Oct 2010
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    Location: AL gulf coast

    rberrey Senior Member

    Agree with fallguy , lots of plans out there , Wood,s plans are good , but for a camper in that size I would look at the ECO 5.5 , or ECO 6 from K-designs catamarans .
     
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  13. bajansailor
    Joined: Oct 2007
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    Location: Barbados

    bajansailor Marine Surveyor

    Bernd Kohler's ECO power cat designs are available from Duckworks - Plans & Kits - Plans by designer - Bernd Kohler - Page 1 - Duckworks Boat Builders Supply https://duckworks.com/bernd-kohler/

    @Slimes I would agree with rberry that one of these ECO cats would probably be much more suitable for what you want, rather than the model shown in your first post above.
     
    Igor likes this.
  14. rberrey
    Joined: Oct 2010
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    Location: AL gulf coast

    rberrey Senior Member

    I would think a boat like the ECO sail cats or a Jarcat would make more since for a camp cruiser and fishing boat than an open catamaran will . And the price of the ECO cats plans are very reasonable .
     
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  15. oldmulti
    Joined: May 2019
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    Location: australia

    oldmulti Senior Member

    Hi. Woods Chat 18 could be suitable. Seek and you will find much information about this design. It will be an easy build from the experiences of several builders.
     
    BlueBell, bajansailor and C. Dog like this.
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