Building 44' wooden tri with traditional planking

Discussion in 'Multihulls' started by Muzammal, Apr 19, 2021.

  1. guzzis3
    Joined: Nov 2009
    Posts: 532
    Likes: 56, Points: 28, Legacy Rep: 42
    Location: Brisbane

    guzzis3 Senior Member

    Just a thought. If you are looking at a design that can be build in solid glass or foam sandwich it would be worth getting a quote from utek in china. I can build in foam sandwich with supplies from them for less than plywood here in australia (assuming proper marine ply). Even if you can get the timber for free the work to build the boat seal it and maintain it will be significant. It's easy to build in flat panel off a table, no molds required. Some flat panel boats can be quite pretty.

    I may have missed something above but why a tri and not a catamaran ?

    Sailing Catamarans - Skoota 36 comfortable live aboard cruiser or day charter http://sailingcatamarans.com/index.php/designs-2/6-powercats/265-skoota-36

    Anyway good luck.
     
    bajansailor likes this.
  2. Rumars
    Joined: Mar 2013
    Posts: 1,078
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    Location: Germany

    Rumars Senior Member

    Muzammal, please understand, one square meter of 4mm thick steel is 1.1kg lighter then one square meter of 50mm thick dry teak wood (steel 31.4kg and teak 32.5kg). In practice, with wet wood and even higher density woods for framing like shisham and kikar such a boat would be even heavier then the same boat buildt in steel (and you don't need 4mm steel for your boat, 3mm and even less would be enough). If you don't believe me, do the math yourself, metric or imperial.

    I am not saying you should build in steel, I am saying you should not build with 50mm thick wooden planking (unless of course you can buy wood that is in the 325kg/cubic meter range). The indonesian method of boatbuilding can work to approximately 30mm thickness (with steel plank to plank fasteners), but only if you have experienced workers and very good wood. Even so, 30mm is more then your boat needs, the total plank thickness should be around 25mm (one inch) average. To do that you need to change the build method, from the indonesian one to something more suitable for you. Given that this is a fast motorboat, the appropiate methods would be: some form of double planking, batten seam, traditional strip planking with nails. What you don't want to do, is build a carvel planked high speed craft, not even a slender, non-planing one.

    I order for your 44ft boat to achieve your desired speed of 25kn, it either has a waterline beam of less then 8 feet, or it must plane and have an engine big enough to do so. It's your choice, but in my opinion a planing trimaran makes no sense, so I advise you to keep the waterline beam to a maximum of 5ft.
     
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  3. oldmulti
    Joined: May 2019
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    Location: australia

    oldmulti Senior Member

    Muzammal. As requested the jpegs of Neap Tide power cruiser and some jpegs of the 40 foot yacht.
     

    Attached Files:

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  4. Muzammal
    Joined: Dec 2020
    Posts: 9
    Likes: 0, Points: 1
    Location: Pakistan

    Muzammal Junior Member

    Your information is precious to me, this all means that I have to find some reliable building standards which can both save weight and money for me.. thats good and I am on it. Soon I will come to some conclusion after which I can start my project. Thanks
     
  5. Muzammal
    Joined: Dec 2020
    Posts: 9
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    Location: Pakistan

    Muzammal Junior Member

    Thanks thanks amd thansk alot dear, this makes a lot of sense. I will review this whole plans again and again to clear-cut inderstanding of every aspect. I have prepared a pdf file of these jpegs and prints will be ready soon ( haha). For an amateur like me, it is necessary to go through this plan multiple time with great concentration.
    Thanks ol multi, You helped me in a great way. Regards
     

  6. Dejay
    Joined: Mar 2018
    Posts: 646
    Likes: 121, Points: 43
    Location: Europe

    Dejay Senior Newbie

    Check out this 38 Trimaran Trawler by Kurt Hughes and oldmulti's thoughts on it. It uses 20mm foam core or 4mm plywood +12 core + 4mm plywood for the main hull plus fiberglass sheeting with epoxy.

    I am a newbie myself so please don't consider this advice, but I assume you could replace that with 20mm planking if you use triaxial fiberglass in the other fibre directions. Maybe even less might do with more stringers and bulkwards. You could probably also only glass near the waterline, or up to the connecting structure. I'm not sure how much strength thin 200 g/m² fiberglass actually adds.

    Also consider that more weight equals bigger engine and higher costs for fuel. For 20 knots you would already need very big engines. So over-engineering and adding weight might not be the cheapest.

    If you can get wood for much cheaper in local currency or through barter and importing even a little fiberglass / epoxy is just not possible, then this advice won't help you of course. But I'd at least check if you can import the stuff through alibaba from utek and get a quote. See this thread.

    From what I've learned, the way to design an efficient power trimaran is to have a rather narrow waterline and a narrow corridor and the hull flares out higher up so you have "shelf space". For a narrow trimaran a V-hull and deadrise is also not that important. But more important that narrowness is length and light weight.

    If you do want an 8' beam for the main hull you are already near monohull territory and could look for "LDL" trawler designs (low displacement / length ratio) and maybe add amas.

    Also your sketch shows a hard corner in the waterline which adds resistance to the water. For lower speeds a canoe shaped stern waterline would be better too I believe. Not sure about higher speeds.

    Maybe you could also look up a pakistan university with a marine architects department and find people that might be interested in helping with a design that can be cheaply build with local woods.

    You should also clarify what you need the boat for, and where, and what it needs to do.

    Unfortunately boat design is very hard. Best of luck!
     
    bajansailor likes this.
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