Trailerable Power Trimaran Design

Discussion in 'Boat Design' started by 4134me, Nov 17, 2012.

  1. 4134me
    Joined: Nov 2012
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    4134me Junior Member

    Hello everyone,

    New here. I am currently in the process of gathering info to begin designing my next boat. I have built in alloy before but only to plan, never my own design. I have an idea in my head which is for a very narrow hulled power trimaran of around 10m length, with folding amas to allow for the boat to be trailerable(2.5m max width here in nz) I will be using a single inboard diesel engine of 150-200hp. shaft drive if I can make it trailer friendly otherwise stern drive. Looking at using a 1.9 tdi for a powerplant which should give decent top speed but more importantly a very economical cruise at 6-10k for the boats main purpose of game fishing. I am hoping to end up with a vessel much better suited to slow trolling in offshore conditions than the common 6-10m planing trailerboat. Being trailerable is a huge advantage cost wise when compared to some of the larger launches used for gamefishing, plus being able to get out to the grounds at a decent speed but not needing thousands of litres of diesel to do it.

    Anyway the reason I am here is that while I have got a reasonable idea of the overall design of the topsides and folding mechanism, I have absolutely no idea where to start with the hull shape and required buoyancy etc. does anyone know of any similar designs I could start with?

    Any advice would be greatly appreciated!

    Thanks.
    Adam.
     
  2. eyschulman
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    eyschulman Senior Member

    buy Kurt Hughes sailing design book. There are some motor tris. Look at the way some boats have narrow waterline width and step flair one or two times out to provide more living space also observe wing compartments extending lateral to hull for berths etc.
     
  3. Steve W
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    Steve W Senior Member

    Welcome Adam, Interesting concept,i can see the merit. Kurt Hughes has a few power Tri designs that may be a good place to start, are you talking VW tdi? i think this would be a great powerplant for a boat, i drive TDI passats and love the engines, anybody down there marinising them?

    Steve.
     
  4. Mr Efficiency
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    Mr Efficiency Senior Member

    What kind of cruise speed are you wanting ? 6-10knots is a fast trolling speed, but presumably you want to go quicker when travelling back and forth to the fishing grounds.
     
  5. 4134me
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    4134me Junior Member

    Cheers for the replies everyone, I will look into those books.

    Yes the VW, they are actually being sold in marine form these days but i have also heard about the vehicle engines being marinised with great success. I am hoping for a cruise speed of around 20 knots. it is uncommon to be able to go much faster with our sea conditions anyway.

    I think i have worked out how the accomodations etc will be set out, thinking about maybe even a small flybridge dedicated to driving the boat and a couple of berths etc down below with access set well down into the narrow hull.
     
  6. groper
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    groper Senior Member

    Great idea!

    Ive done the exact same thing but with a catamaran powered by 90hp outboards... i cant trailer it tho, its 5.1m beam... your tri idea sounds just perfect for a similar use, but trailerable...

    Youd want to go along the nigel irens design ideas i think, just instead using folding amas instead of fixed.... borrow the idea from the folding farrier sailing tris (even buy the aluminium mechanisms from him) and your good to go.... first decent idea ive seen on here in a while.... nobody can afford to run the extremely heavy, gas guzzling game designs from yesteryear...
     
  7. Squidly-Diddly
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    Squidly-Diddly Senior Member

    see my gallery for rough concept.

    This one shows a 8' wide unit in center with 4' wide hulls on either side, mostly because the the cat is sort of the main starting point of the concept.

    However, a single 8' wide hull with much smaller amas could work. The mast is the trailer frame.

    This wouldn't be as quick to deploy but would be easily upgradable strength-wise for offshore.


    http://www.boatdesign.net/gallery/showphoto.php/photo/17328/ppuser/22518
     
  8. eyschulman
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    eyschulman Senior Member

    Just remember the primary rule with multi hulls keep it light or it will be a piggy. when you start adding things like FB-large tanks-and other luxury items you loose a lot of the reason to go multi
     
  9. groper
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    groper Senior Member

    I think he is thinking more along these lines;

    [​IMG]

    The most difficult part of the whole thing, is to get the back deck layout right so that its well setup for game fishing. This is more difficlut on this type of vessel, as the beam is much narrower than a traditional game fishing mono.

    4134me, the reason this type of design is very efficient (such as Earthrace or Ady Gil and other "stabilised monos") is they all must have the following.

    1. Lightweight and long waterline length - in naval architecture the term is DLR or displacement length ratio.

    2. The waterline beam of all the hulls including the main hull, is very long and narrow - again in tech terms - a high length to beam ratio.

    Keeping the boat light is easy enough provided its engineered and built accordingly - similar methods to most performance sailing multis ie thin ply and glass or composite sandwich construction.

    THe difficult part as i see it, is making the narrow beam of the main hull, into a workable space for a good fishing arrangement. Not impossible, just needs a good deal of thought and planning so you end up with a boat that performs well, and still gives you a good amount of fishing room. Working with narrow hulls is always difficult to get the most out of the small space.
     
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  10. Steve W
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    Steve W Senior Member

    I would be more inclined to use a folding system where the amas fold in alongside the hulls rather than the Farrier system which, brilliant as it is really doesnt allow for marina berthing unless you are willing to antifoul the ama topsides. There is a nice youtube video of a dragonfly tri folding which is very slick and would work even better with the tiny amas of a power tri.

    Steve.
     
  11. 4134me
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    4134me Junior Member

    Thanks for the vote of confidence groper! It was the Ilan voyager and its impressive performance/economy figures which put me onto the idea in the first place. I think I will have the amas closer to the rear such as in Craig Loomes' wave piercing designs:

    http://www.lomocean.com/projects/cutting edge/12m - azzum

    obviously it will look very different to these futuristic machines but with similar yet foldable amas I think I should be able to design decent rear deck space into it, even if part of it is vertical while folded. the downside will be the rear deck being well off the water but I should be able to have a lower boarding platform with access down through the rear of the central hull. I don't expect to end up with anything as fishable as a large launch but will be happy with something like in a similar size planning mono.

    weight should not be too much of an issue, as it will be only used for short trips, at most a couple of days and mostly at efficient trolling speeds I will not need huge fuel and water tanks, the interior will be kept simple and lightweight.

    any input greatly appreciated!
     
  12. Number4

    Number4 Previous Member

  13. groper
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    groper Senior Member

    Yep, you could flare the topsides out to form a fishing platform above the water... with a displacement catamaran you end up with the same thing... you cant get the floor down at the waterline level like you can on a mono, so the fishing space and layout is completely different....

    Those craig loomes designs are not the same beast like nigel irens.... they look similar, but really are different. Have a look at the horsepower required by the loomes designs, much higher than irens... the irens designs have a more slender hull and need less horsepower for the same speeds. More seperation of the amas = less wave interference drag, esp at trolling speeds.

    Your link to the Loomes "azzum", installed horsepower = 740. surface drives... What more do you need to say??? its just another gas guzzler with a modern look...

    If you want this thing to be efficient and fast on small horsepower engine, the design is quite specific, and very sensitive to mistakes or compromises...
     
  14. 4134me
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    4134me Junior Member

    Hi Groper

    Yes will be very different to 'azzum' but with amas in a similar position to aid in setting up a decent rear deck for fishing. I am hoping that my 150-200hp will be more than sufficient, likely overkill at times. the economy figures coming from the planing trailerboats using the tdi engine are very impressive, especially while trolling. So hopefully I should be able to improve on this further by using a hull shape better suited to those speeds!
     

  15. groper
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    groper Senior Member

    Indeed, but do you know what the hull shape is, thats better suited to those speeds?

    Planing designs can also be efficient, again if you keep the weight out of it they can be good on fuel also in the higher speed regime, but i dont like the bumpy ride...

    Will you design it, or home build it, or are you looking for a designer to do it for you?

    For your hull shape, the wave making resistance decreases rapidly with decreasing waterline beam of your hulls. So if you keep your length to beam ratio higher, it will be more efficient. It will need to be very full in the midbody, with close to a flat bottom and vertical sides (high block coefficient) in order to maximize the displacement whilst keeping the waterline beam minimal.
    The stern will be very close if not the same fullness to the midbody for a higher prismatic coefficient and pitching control.
    The bow will be very fine entry due to the high length beam ratio, like a knife, and it wont pound in the chop.

    similar concept to perforamance sailing tris like this, which show all the same design elements including the flared topsides to get more space up on deck - except of course you will have much smaller amas as you dont need the righting moment;

    [​IMG]
    [​IMG]
     
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