Catamarna plans as base for building a trimaran

Discussion in 'Multihulls' started by neptunkryssare, Mar 2, 2014.

  1. neptunkryssare
    Joined: Sep 2009
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    Location: Stockholm, Sweden

    neptunkryssare Peter

    I am planning to build a trimaran that could have close to the same performance as a class A cat.
    As I have not found any good plans for a trimaran of that type I think the best one could do is to use plans for an A-class catamaran and convert those plans to be a trimaran.
    Maybe build it as a catamaran first, the convert it to trimaran.?
    How much would that the comvesion job slow down the complete process.?
    Could one build it so one can switch between catamaran / trimaran. Eg remove the centerhull and use the same or other trampoline.?

    I plan to sail in wind between small brise up to 10-12 sekundmeter.

    My weight is about 70-90 kg, (My weight goes up and down, don't really care about it. It's like the weather to me - it changes) and I plan to sail mostly singlehanded. Sometimes with my son which weight is about 60 kg.

    If I build the sidehulls small I guess the buildingtime would go faster, and I could have the trimaran built in one piece.
    I am also open to build a boat with floats as the same or almost the same size of the mainhull

    The dissadvantage to that would be - longer building time.
    The added weight would maybe make the boat to heavy if I would like to add foils.?
    Foils would come later, basically because I donẗ have the money. And if I make the hulls detacchable, then it's no big deal if I build it with bigger floats from the beginning.

    I know there are free old tornado "plans" out, and I have downloaded them - but as a first-timer I don't have the right knoweledge to construct a boat from theese.
    Also - the tornado with it's 6.09 meter is a little bit to large for my building environment (living room converted to workshop).

    So these boats is what I think would be the closest to go from.
    taipan 4.9 metre catamaran
    mosquito 5 metre catamaran
    unicorn 5.49 mete catamaran

    There are a few more that could fit for this project. But I have not been able to reach thoose that sell the plans.

    And it will take a while until I can get started - because my son is building a boat and I have to put all my money to that project for a few months more.

    As comes to comfort - I have two ideas.
    Minimal comfort, a hole to stuck my feets to.
    Bare comfort, if not affecting the performance to much - a minimal cockpit, eg just a hole in the centerhull and a plank to sit on.

    Also - I would like to build the boat so ther should not be to easy to pitchpole.
    Baltic Bandit likes this.
  2. Doug Lord
    Joined: May 2009
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    Location: Cocoa, Florida

    Doug Lord Flight Ready


    Welcome to the forum, Peter! Look thru this forum there are lots of small tri's and discussion of same. Look at the EC Challenge thread and I believe there is a thread called "Trimarans of the Everglades Challenge".
    Seems to me you've got to give a lot more thought to the things you want out of the boat:
    1) do you want the boat to be as fast as an A Class? If so you'll be likely to need small amas and ultralight construction.
    2) do you want the main hull to fly? This goes with #1 and will be a requirement to be faster than an A Class.
    3) If you choose to go with a wide trimaran you can either have humongus sail area or have moderately high sail area but have the crew sit in the center. My definition of wide is square or over square. Look at the "Bradfields Osprey" thread: LOA 18', Beam 22' weight 400 lb.and it is a foiler. (last page-check out the whole thread)
    4) Foils: you can use small foils to fly the main hull of a wide trimaran in light air. You can use a foil attached to the bottom of a flat bottom ama to effectively increase the lifting capacity of a small ama. See the last page of the MPX thread for some ideas. posts 993-997
    5) Main Hull: you can go with a skinny main hull or with a wider planing main hull(like the WETA and my Test Model and others). In small boats, the wider hull allows a bit of extra room but, unless you use hydrofoils*, the skinny hull would probably be better for high performance. The two full size tris(14' & 20') I've built both used planing hulls. Make sure you carefully estimate weight or have a design that has been proven. Too much weight can seriously dampen performance.
    *Hydrofoils-unless a very simple system-are not a good idea for a beginner. The require a lot of knowledge of design and construction to properly implement.
    First of all you need to study the available trimarans and their designs and make notes about the ones you like. Try to narrow down the performance you really want and don't forget: the higher performance the more expensive
    it will be and the more skill that will be required to design and build it.
    Various links-click : trimaran in picture below
    click for better view-also check out this year and last years EC threads:

    Attached Files:

  3. neptunkryssare
    Joined: Sep 2009
    Posts: 55
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    Location: Stockholm, Sweden

    neptunkryssare Peter

    Thankyou for your reply Doug.
    I can say this, to quote you from the small trimans thread which I have beeen reading a few times the latest days.

    "I think fast "daysailing" in a foil assisted oversquare tri while sitting on the side of a comfortable cockpit and not having to run side to side with every tack or gybe while you pass the beachcats would be a blast. ".
    There you pretty much summarize what I want.

    I am just not sure that I am able to buy or product foils, so my intention is to make a tri that is as fast as possible to use without foils. And if possible, add foils later.

    And for the points you put out to me.
    1) do you want the boat to be as fast as an A Class? If so you'll be likely to need small amas and ultralight construction

    I would it to be as fast as possible within the limitations of using plywood. Preferable method. Stitch and glue.

    2) do you want the main hull to fly?

    Yes, but there again comes my doubt how I can afford to buy foils, and if I am capable of making foils.

    Also I am not sure, how small the hulls can be and - without foils, still be able to let the mainhull fly.?


    The crew should be mostly me. Singlehanded sailing. But my wish is that I could have a one or two onboard for a more limited sailing experience. Or just one as crew, and with larger sail.

    Foils at the bottom of the ama sounds like a solution to me, but I am afraid that I will got stuck in that process. Is it possible add that foil later.?

    Oh, yes. I would like the boat to be as small as possible. If possible - below five metre in length..

    Now I will go and read the threads that you suggested. I guess I come back adding more.
  4. Doug Lord
    Joined: May 2009
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    Location: Cocoa, Florida

    Doug Lord Flight Ready

    I think you should find a small tri you like that has plans for sale. What did you think of the TRIKA 560 I posted a picture of? Here is more on it: I would suggest that you do the studying I suggested and compile a list of your requirements with an emphasis on
    how important your requirents are relative to cost. Then write to the designer and see what he says. The 560 seems like the crossarms are on the small side but I'm not positive-I'd have to know more. And I would tend to want to go with flat bottom amas though the 560's look pretty good. The single "DSS" foil could be added later at the chine going across the hull. The flat bottom would allow the foil to be attached w/o penetrating the hull-making it easy to design a way to add and remove the foil simply. If you can try to build a relationship with a designer-like the 560 designer- you would be ahead of the game.
    But before you know whether the 560 is close to what you want you have to have a clear, concise understanding of what you want in a small tri and then look at the specs and see what, if any, changes would have to be made to achieve you ideal tri.
    One thing you should be aware of is that there are few ,if any, tris under 20' designed to fly the main hull and/or designed with foils. I feel that is a gaping hole in small multihull design because an oversquare small tri designed specifically to use foils has an excellent chance of being the fastest type of small multihull-and not only that it can also have a degree of comfort just not associated with high performance small boats. Needless to say there are people that say this is not possible
    but they're simply wrong. Just keep this mindset in mind as you talk to designers!
    560 basic specs:
    » Main Hull length: 5.60 m (18’4”)
    » Min Hull Beam: 0.70 m (27.5”)
    » Displacement to DWL: 250 kg (550 lbs)
    » Ama Length: 4.06 m (13’4”)
    » Ama buoyancy (each): 150 liter (330 lbs)
    » Ama beam: 0.25 m (9.8”)
    » Sailing Weight: 87 kg (192 lbs) incl. Mirage Drive + Well (Without Mirage Drive and well it would be approx. 9 lbs lighter.)
    I'm amazed it doesn't give overall beam or sail area(!)-but maybe if you look closer you'll find it. The main hull is a bit longer than you say you want but I'd try to go for it because the amas are small-and the longer the main hull the narrower it can be and the less resistance it will have.
    This doesn't have to be the boat you want-it's just a start from a designer who seems willing to work with a customer.
    Just for the hell of it you might want to talk over your ideas with Richard Woods, a designer who is a member here and has a great deal of experience. If you decide on a more high performance oriented design Eric Sponberg is a naval architect and marine engineer with an open mind who is willing to bill hourly. He is a pleasure to deal with and can help with important engineering questions like the size of the cross arms etc. depending on whether or not you find a suitable designer that already offers plans. He has helped me a lot on several projects and is a key member of the Team which will help me with building the Crossbow fl movable ballast monohull I hope to build next. I'm doing this next because I believe it has the potential to help disabled and physicaly restricted people to do a type of high performance self righting monohull sailing that they can't safely do now. After that, I want to do a 16-18' singlehanded high performance tri based on what I learn from the Test Model and what I've learned from my previous tris and the numerous other boats I've built-a sort of "super tri" I hope.....So I'll be as much help as I can and watch what you come up with carefully.
  5. Baltic Bandit

    Baltic Bandit Previous Member

    If this is your first project - just build it. It will not be as good as you hope and it will be much more expensive than buying a boat of equivalent finish - so the only reasons to build are
    • You cannot find the kind of boat you want and you have a good design
    • You cannot get a used boat shipped to you at a reasonable price (ie you live in the Falklands or the RSA coast)
    • You LIKE building boats
    None of this seems to apply to you.

    As for smaller Amas reducing your build time. That simply is not true. Hull building is a tiny fraction of the build time of anything. Finish work is the major component and that doesn't really change with size.

    The limits of your build shop are understood, but if you build a hull on the diagonal of your room you might well be able to build something larger. There also are kits that you can buy that in the end will be less expensive than you trying to cobble together something.

    For example Doug has spent 4+ years building a model of the boat he wants to build. So if you choose to build for reasons other than you love to build, you are likely to not finish the project.

    In fact the boat you are describing already exists. Its called a Weta. and there are used ones for sale. the Swedish distributor is

    So for roughly 97,000 Kroner (11,000 Euro) you could have a boat that does what you want, has a trailer, all the sails and works.

    Work out your budget for a build.
    • Your mast will cost 2,000 Euro by the time it is fully rigged and fitted
    • Your sails (Main, Jib, gennaker) will cost 3,000 Euro
    • The materials for your hulls will cost between 1,000 euro (plywood stitch and glue technique) to 3,000 (for carbon fiber)
    • a trailer and a beach trolley adds another 2,000 euro
    • Trampoline and cross bars and such 1,000 Euro
    • foils - 3,000 euro
    Notice that adds up to 12,000 Euro. More than it will cost to buy a Weta.

    Oh and whatever design you come up with it will not be
    • Self Rightable the way a Weta is
    • Sail as well as a Weta (since you won't have all the hours of tuning that have gone into a Weta)
    • warranteed

    And note, I have no association with Weta - I just love to sail and hate seeing folks start a boat project when they would rather be sailing
  6. oldsailor7
    Joined: May 2008
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    Location: Sydney Australia

    oldsailor7 Senior Member

    The perfect Tri for your requirements is the 5M Piver Frolic. Plans available from the Maritime Museum for a very little price.
    It is simple to build, and has planing amas. I'ts BOA is 50% (2.5M), only to make it trail-able without folding. It can be built with 70% BOA, or greater if you extend the crossarms. You can still make it trail-able if you do, by hinging the crossarms to fold over the deck like a Piver Nugget or Cross 18.
    I built one for my teen age son. It was very fast. He sailed it in all weathers.
    We lived in a high rise apartment and I built it in my underground car space. It was that easy. I highly recommend it. :D

  7. Baltic Bandit

    Baltic Bandit Previous Member

    Does the Frolic self-right?
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