Tropical Wood Catamaran Boat

Discussion in 'Boat Design' started by somarine, May 16, 2020.

  1. somarine
    Joined: May 2020
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    somarine Junior Member

    Hi All,
    This forum has been been helpful for my quest to build a catamaran boat with Tropical wood. I read so many article about the good, the bad and the ugly about why wood is a bad material for building a boat. I quiet remember how i was a small boy fishing with my uncle on the Lake volta (the largest man made lake in the world) using wooden canoes.

    I need advice from this forum since the forum has inspired me to design my catamaran using MS excel
    I attached some details of my boat as a novice.
    I will accept suggestion and corrections
     

    Attached Files:

    • 10m.xls
      10m.xls
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  2. upchurchmr
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    upchurchmr Senior Member

    Good luck.
    How are you going to build the hull?
    What kind of wood construction?

    Most people do better buying plans, but have fun.
     
  3. somarine
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    somarine Junior Member

    Hi upchurchmr,
    I am thinking of Building the hull with Cedar or Mahogany and build the Deck with Plywood.
    Of Cause I plan to glass the Hull
    Thanks
     
  4. upchurchmr
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    upchurchmr Senior Member

    Strip planked?
    Caravel?
    Epoxy?
    10' or 40'?
    Sail or power?
    How far will you be going?
     
  5. bajansailor
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    bajansailor Marine Surveyor

    Welcome to the Forum Somarine re your first two posts above (even though you have been a long time lurker).
    Re suggestions concerning your design - do you REALLY want to build your own design?
    What is your next step in the design, beyond the Excel file that you attached?

    Please may I offer you a suggestion - if you want a reference vessel to work from, re carrying on with your Excel design, at least download the free study plans for the Skoota 32 in the link below -
    Sailing Catamarans - Skoota 32 live aboard cruiser http://sailingcatamarans.com/index.php/designs-2/6-powercats/469-skoota-32

    And scrap that cat which you have drawn in Excel. You could start drawing it again, using the Skoota 32 as a basis.
    What is your budget for building this cat?
    Fallguy on this forum is currently building a Skoota 32, and although he is building her in foam sandwich which will probably be more expensive than timber and plywood, I think he did mention in one of his posts that he has already spent something like US$ 130,000 in materials alone, and he is still quite a long way from completion.
    When you look at it from this perspective, the cost of a professionally drawn set of plans for your boat will be a tiny fraction of the final cost.
    And if you buy a set of plans, you can be guaranteed that this boat will do what it has been designed to do, provided that you follow the instructions and don't make it too heavy.

    In a nutshell, what I am saying is please do consider buying a set of plans rather than trying to design the boat yourself - power cats are complex beasts to design and to build, and you will be very grateful in the end that you did invest initially in a set of plans from a designer with a very sound reputation.

    Edit - I just saw Upchurch's note above.
    I think he means 10 metres - I calculated the overall length of the cat in the Excel drawing as just under 11 metres, if I use the double berth shown as having a length of 2 metres.
     
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  6. somarine
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    somarine Junior Member

    Hi upchurchmr,
    Strip planked? YES
    Caravel? NO
    Epoxy? YES
    10' or 40'? 40'
    Sail or power? POWER
    How far will you be going? ONLY FOR DAY TRIP A RIDE ABOUT 5HRS
     
  7. somarine
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    somarine Junior Member

    Hi bajansailor,
    Thanks for your respond and kind advice.
    Please tell me what is wrong with my design in the first. I know this is not drawn to scale.
    I wish I could build my own design but I also know as a starter it will be a Herculean task to build such a project.
    Budget, I have not put a number on the project yet.
    I build a prototype that my child ride on our home swim pool.
    Your study plan is some how impressive
     
  8. bajansailor
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    bajansailor Marine Surveyor

    Hello Somarine,
    Re what is 'wrong' with your design (so far) - ummm, well, for a start I wouldn't call something sketched in Excel a design - you still have a LONG way to go to develop this into a workable design that you can build from.
    Compare your design with the Skoota, and other similar power cats around 30' - 40' in length - you mention a length of 40', but I was thinking that the 10m referred to 10 metres.
    And before you do anything else, you have to establish what your budget will be for this vessel.
    And establish a 'Statement of Requirements' - I am sure that you have often seen this mentioned in the past, and it is important.
    You mention that you want a power cat, and that it has to be capable of "ONLY FOR DAY TRIP A RIDE ABOUT 5HRS"
    If this is really the case, do you really need a 40' power cat to do this job?
    A much smaller boat would do the job, and cost a fraction of the amount to build a 40' (or even a 32') cat.

    Have you got a photo that you can post of the prototype model that you built?

    Edit - Have a look also at the Schionning range of power cats -
    http://www.schionningdesigns.com.au/powerdesigns
    And do some googling - there are many other wonderful designs out there as well.
     
    Last edited: May 16, 2020
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  9. Mr Efficiency
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    Mr Efficiency Senior Member

    Is that right, bajansailor, that fallguy is $130k in, on materials alone ? Surely not ! :eek:
    Somarine, if you want to build a boat from wood strips, I really think a chineless design will make life a lot easier, those little discontinuities would, to my way of thinking, complicate matters. But it may still be doable. I am quite taken with the idea of getting longitudinal strength from strip planks, and getting the integrity of that shell bolstered by glass epoxy that is directionally more biased toward the athwartship direction.
     
  10. upchurchmr
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    upchurchmr Senior Member

    If you are doing a canoe sized strip plank then chines are no problem. Around 1/4" thick.
    Just a little learning about how to taper/end a strip - takes about two tries to get it right. Very easy if you are going to paint, harder if you are going to varnish.
    Typically you use plain woven glass, so there is no biasing the fabric in any direction.

    If you require bigger strips (edge nailed for strength) I don't know what to suggest.
    I haven't tried that, but there are other self proclaimed experts who should be along.
     
  11. fallguy
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    fallguy Senior Member

    Probably one of the best boat designs available in the range you like is the Skoota 36. It is an incredible boat. The best way to build it, however, is plywood on frame as drawn by Woods.

    But the SOR confuses me a bit. That is a LOT of boat for a 5 hour day trip. Lot of boat to slip, build, budget.

    I would really recommend you consider a Skoota 30 with F70 Yamahas. It will be a special boat, fast for a displacement vessel, seaworthy, economical to run, nice lodging spaces.

    Designing your own boat is a fool's game. If your hull designs are too wide forward, or have some other flaw; all your efforts in fitouts will be done on a boat that performs poorly.

    If you want the sor to be something more like a vessel with a 2 day range; say 500-1000 miles; the Skoota 36 is a better boat, more expensive to build. A builder in England started one and I believe he passed away before completion. The reason I mention is his boat was extended to 40 feet somehow. Richard would know details.

    I believe Richard may be willing to draw the Skootas in strip. Ask.

    As for my budget, the final budget is the $130k number I'd say. We are at sunk cost at this point. A foam boat is very expensive to build. Our epoxy costs are very near or exceed $30,000. Quite frightening...I was very ill a month ago and had visions of my wife calling the dump.

    While Skootas may be buildable in strip; they shine as ply boats because they are dev panel.

    If I had built in ply; the boat would be heavier, but in the water this summer instead of next and far, far cheaper.

    Strip is faster than foam, but slower than ply.

    One of my memories of tropical boat building with wood is the guy that build his boat out in the tropics over a couple years, encapsulated it all in epoxy or esters and then the damn thing rotted from the inside out. He realized that all the wood had gone to equilibrium at 20-30% prior to encapsulation. For a year or two; he was utterly confused about how his boat could be rotting piece by piece outside pieces faster than the deeper ones. But as it progressed; he realized his error and there was little to be done about it. I never did hear the final story on that boat. Be careful. Wood does find eq.
     
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  12. bajansailor
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    bajansailor Marine Surveyor

    Hopefully Fallguy will be along later to either confirm or deny this, but I remember being quite astounded at the materials cost that he had mentioned in one of his posts re his Skoota.
    Edit - he just beat me re his post above, excellent!

    I have a feeling that the cost of 'disposables' when infusing and vacuum bagging must be rather high (relatively), especially when compared to ply / epoxy and more traditional types of fibreglass lay-up.
    And yes, I know nothing at all about vacuum bagging and infusing - I tip my lid to Fall Guy re the work he is doing on his fine cat.
     
  13. fallguy
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    fallguy Senior Member

    The deal with vac bagging is the wet work requires more than 100% epoxy to glass and the final ratios are low. So there is a lot wasted in epoxy, peelplies, breather media, time to build one panel a day versus a few days of sheathing an entire hull. I figure our waste rates on epoxy are in the neighborhood of about 25-35%, or ito $s, $7500-$10k in the trash. Of course, this parlays to a faster boat speed, but a hard pill indeed.
     
  14. Mr Efficiency
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    Mr Efficiency Senior Member

    Can you expand on this ? You are saying the wood was encapsulated when not properly seasoned, with excess moisture content ?
     

  15. Mr Efficiency
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    Mr Efficiency Senior Member

    It is a lot, as much as I like cored GRP, that sort of expenditure is testing the romance.
     
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