Power Trimarans?

Discussion in 'Powerboats' started by CatBuilder, Jul 23, 2009.

  1. CatBuilder

    CatBuilder Previous Member

    You don't see so many power trimarans. Does anyone know of some example power trimarans that are either:

    a) Built to plane with more efficiency


    b) Built as extremely efficient trawlers

    If there are none that fit these descriptions, what is it about trimarans that prevent one from making them behaving something like a power cat?

    Also, in the same general theme, can anyone describe the differences between a power trimaran and a very narrow beam long waterline monohull? Could the long waterline narrow beam mono be used as an efficient trawler?

    Sorry... I'm new to power boats and new to the area of designing boats. I come from a background of sailing monos and cats.
  2. apex1

    apex1 Guest


    when you´re through with it, you´ll likely convert to the motor community (like me). 38 years ago

  3. CatBuilder

    CatBuilder Previous Member

    Thanks, Richard. I was already a fan of that one. I feel a conversion coming on and have found more than enough reading in the long skinny boat threads on here. I'll just keep on doing the reading until I can ask some better questions.
  4. Doug Lord
    Joined: May 2009
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    Doug Lord Flight Ready

    Power Tris

    Here are a few--Ilan Voyager and a couple others:

    Attached Files:

  5. Guest625101138

    Guest625101138 Previous Member

    Attached images show the best known power tri. Currently holds the fastest round-the-world power boat record. Only a few days slower than the big sailing tris although it took a slightly shorter route and avoided the really heavy weather.

    Rick W

    Attached Files:

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    FAST FRED Senior Member

    Once again the real question is the actual USE the boat will be called on to perform.

    For someone wishing to do a FAST efficient long cruise the skinny monohull, with or without "training wheels (tri) would be first choice.

    BUT as a living , entertaining platform, mere area is a plus , so a big box cat, regardless of the efficiency or deep ocean hassles is usually selected.

    Mental ************ is great fun , but a boat to be USED , needs to know realistically, HOW it will be used.

  7. CatBuilder

    CatBuilder Previous Member

    Thanks, Fast Fred. I saw all of your posts in the narrow boat thread.

    I'm looking to use the boat coastal (near shore) only. I'm also using it as a liveaboard/coastal cruiser for two people.

    If I might make a comparison to RVs, I would be looking for a Road Trek RV instead of a Class A motorhome.

    (Road Trek is a van all tricked out to be an RV. Not much space, but fits anywhere, great on gas, etc...)

  8. marshmat
    Joined: Apr 2005
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    marshmat Senior Member

    Hi CatBuilder,

    Looking at the ideas you started off with at the top of the thread:

    "a) Built to plane with more efficiency"

    Well, there have certainly been some interesting trimaran-like power boats that do "plane", in a manner of speaking. There are those "gull wing" or "cathedral" hulls you see on some '60s and '70s bowriders, and which survives, in spirit, in today's Boston Whalers. But there's a strong argument that the shape is just a deep-V with a really huge reverse chine, not a trimaran. Also on the radar would be larger surface-effect craft (M-ship, etc.) although these aren't "planing" hulls in the sense we normally think of.

    Really, though, the power trimaran's advantages- notably its low drag and its ability to slice through waves without much of a fuss- are largely a function of the fact that its main hull is much longer and narrower than a monohull boat of the same weight. That long, narrow shape isn't really conducive to the low bottom loading and flat running surface that leads to efficient planing. And once on plane, dynamic forces take over that would likely relegate trimaran outriggers to a role somewhere between "questionable" and "redundant". (Of course, this is talking about something that actually looks like a trimaran, 3-point hydros are a different matter).

    And the next idea,
    "b) Built as extremely efficient trawlers"

    Well, as Fred has pointed out, we really need to take a close look at how the boat will be used. When we're looking at powerboats, we don't need the enormous initial stability that is so desirable in a sailboat. Thus, the sailor's main rationale for having outriggers is missing from the powerboat realm.

    So, we need to consider what other characteristics would lead us to a tri-hull configuration for a power yacht. Perhaps we want a long, narrow hull for efficiency and to slice through waves without pounding. We want a decent turn of speed, substantially more than most monohulls can do with a given engine and fuel burn rate. And let's say we also want a fair chunk of deck space, with easy access to the water, places to dump kayaks and water toys, etc. A tri configuration might start to look appealing here. The price that is paid is a more complex structure- an extra two hulls, plus crossbeams- and a package that, unless it folds somehow, will cost you dearly if you need to rent slip space.

    Now, if we don't intend to be goosing the throttle to well past the so-called "hull speed", and the huge trampoline/side deck area of a tri isn't a "must have" feature, and a roomy interior is more of a concern- perhaps sticking with a single hull makes more sense.

    But what it really comes down to is this: What characteristics do you need for the way you plan to use the boat?

    (As an aside, I've been going through the power tri vs. planing mono debate myself over the last few months, albeit for a somewhat different use profile- " http://www.boatdesign.net/forums/projects-proposals/trailer-cruiser-revisited-trimaran-27032.html ." The tri's lower power requirements, resulting longer range, and huge usable side-deck area were the deciding factors there. But, ultimately, you have to weigh the trade-offs for your own project.)
  9. CatBuilder

    CatBuilder Previous Member

    Thanks, Marshmat.

    The more I've been reading, the more I've realized "planing" was the incorrect word. Also, the more I read the more I realize that yes... why does this have to be a trimaran?

    Coming from the sailing world, my gut (not math) tells me that I need a lot of lateral stability. I'm very weak in understanding powering stability for trawler-like displacement hulls.

    So could a 40 foot power boat with a 7 foot beam be built in such a way as to be stable at sea? I'm not sure if that hull form (with a sharp, plumb bow) would even qualify as something you could use as the center of a tri as it might be too beamy?

    Would that type of hull make sense as a mono rather than a tri?

    Lastly, although I have no end to my questions in sight, I'd like to answer the ones you asked about usage. You were very close!:

    1) I'm looking at long, slender boats for efficiency. Speed (to someone coming from sailing) is 8 knots. 10 knots would be incredible! Most of all, I'd like to be able to use low horsepower to achieve fuel efficiency by reaching 8 knots using the minimum of fuel consumption.

    2) I'm presently sailing a catamaran. I sure love the catamaran, but it's an enormous build cost and complexity as a build project. I've refit enough boats to understand what it takes to build an interior and put together systems. However, I absolutely love the initial stability of a catamaran over a mono due to its beam. This is comfortable while underway but even more comfortable at anchor, which is where a boat I come up with will be 90+% of the time. I am another idiot who is thinking about a mono with "training wheels" rather than a real trimaran, I think. :D I see "trimaran" as a way to take a mono and get the stability of a cat. Am I far off?

    3) I'd like to design the boat to be able to cross oceans at 8 knots, but the main requirement is size for portability, access to EU canal systems, etc... If I could develop a boat that could both be an ocean crosser *and* a narrow boat of 40 foot length and 7 foot beam, that is what I'm after, ultimately.

    4) Lastly, as an add on, I'd sure like to have a kite sail to fly to save on power when going downwind in conditions that warrant it.

    Those are the intended uses. Coastal cruising a must, ocean crossing a "nice to have." If I can achieve both, great! If it's just a mono, great! I'm a complete design novice, but a very experienced sailor/liveaboard.

    I know exactly what I *need* out here, but I don't know if it's commercially available, if the hull or a design is available, or if I should design it myself, which I am strongly considering.

    I was to build a cat, but my wife had a change of heart, so I will follow her change of heart and come up with a boat that fits those above criteria. Any help or advice would be welcome. Also, my screen name doesn't fit my situation! ha ha

  10. apex1

    apex1 Guest

  11. Guest625101138

    Guest625101138 Previous Member

    I have been playing around with similar ideas to you. My object is coastal and river cruising. I want something trailerable so I am not going to 40ft. I did go through a phase of looking at a 3-part hull to get length.

    Anyhow someone gave me the idea of what I call a faux-tri. The boat is a long slender monohull underwater, a trimaran on the waterplane and a monohull above the water. See attached image.

    My aim is to do 8kts with less than 1kW. This requires an ambitious weight target but not impossible. The boat is intended to have both solar and wind energy collection, battery energy storage and electric motor propulsion.

    This hull form will achieve the best form stability you can get for a 7ft beam. It is easy to make self-right by placement of the heavy components like batteries.

    Whether it works for you depends on what you want to cram into it. A 40ft boat could be made quite comfortable but the 7ft beam is a serious constraint for getting nice spaces. Much better than the hull of a cat but 10ft would be nice.

    The idea is not new. This link shows something bigger but of similar concept:

    Rick W

    Attached Files:

  12. Crag Cay
    Joined: May 2006
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    Crag Cay Senior Member

    Apart from being too deep and too tall. Hopefully you'll run aground before getting stuck under a bridge. Slightly less embarrassing that way round.
  13. apex1

    apex1 Guest

    These boats are neither nor, you should keep your mouth shut when you do´nt know what you´re talking about! And obviously you do´nt k now European canal sizes!
  14. Crag Cay
    Joined: May 2006
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    Crag Cay Senior Member

    Please then, enlighten us as the the draught and air draught you can carry through the Canal du Nivernais or Villaine, as these are amongst the smaller French canals.

  15. apex1

    apex1 Guest

    Maybe you are just joking (or are you going to split hairs?)
    My statement referred to the fact that the boat is capable of cruising the (Freycinet size) French canals as well as the (much wider) other European ones! It was´nt meant every damp meadow.
    The Nivernais btw is 2,90m air, 1,2m water
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