Propulsion System for Trimaran Design

Discussion in 'Boat Design' started by ayouden, Jul 8, 2018.

  1. ayouden
    Joined: Jul 2018
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    ayouden Junior Member

    Hello all,

    I'm new to any kind of boat design and as such, I've come here to ask for some help on my boat design. (I hope this has been posted in the right section!) As such, my initial ideas might be hopeless, so please forgive me!

    I've been tasked with creating an RC boat which can carry a large payload (3kg-approx), be stable and have a tight turning circle.

    Now, I'll admit that this is for an RC boat around 60cm in length, but I'm assuming that the principles of the design will be the same as that of a 60ft craft!

    With this in mind, I'm after some help or advise on which configuration to go with, or indeed if I'm going down the wrong route all together!

    I'm planning on using some turbine jet drives (Pictured) which have a movable nozzle to direct the water. Just like a Jet-Ski.

    My problem is that I don't know which layout would be best?

    Option 1: x2 medium-sized jets on the outer hulls Option 2: x2 medium-sized jets on the centre hull Option 3 x1 Large jet on the centre hull

    Would anyone happen to have any hints or tips to achieve the highest possible turning circle with these options?

    Link to images: Imgur https://imgur.com/a/deTCrKO

    Thanks!

    Alex

    EDIT: Changed payload from 6kg to 3kg
     
    Last edited: Jul 8, 2018
  2. Doug Lord
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    Doug Lord Flight Ready

    I'd keep the jet(s) in the center hull-the outside hulls may come clear of the water in some conditions. Seems to me that the payload(13.2lb) is too much for such a small boat.(23"!)
    What's the purpose of the model?
     
  3. ayouden
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    ayouden Junior Member

    Ah! It should have been 3kg, rather than 6kg.

    I have edited my post to show this!

    With the boat potentially being quite low in the water due to the weight, I thought that even in the worst conditions they would stay in the water.

    Depends if the outer hull option would give a tighter turn?
     
  4. Doug Lord
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    Doug Lord Flight Ready

    6.6lb is still way too much for a 23" boat! Some guys from Princeton bought one of my sailing tri's back in 2000 to add an autonomous control system that weighed 10 lb. It worked for their purposes but was right at the limit weight wise.
    Scaling that 10lb down to the size of your boat shows that the max weight would be .38lb to be the same proportion of overall weight as my much larger boat. So, I'd suggest that you lengthen your boat or reduce the total payload.
    What is the purpose of your model?

    Flyer 3(68") which was converted to carry an extra 10lb:
    flyer3redfull_small1.jpg
     
  5. ayouden
    Joined: Jul 2018
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    ayouden Junior Member

    I stumbled across a video which shows the style of boat which I'm looking to replicate:



    This looks to be able to carry 6kg, but also looks to be 4ft long rather than my 2ft design!

    I'm creating a custom bait boat, here's a stock image of one: https://www.baitboats.net/media//DSC_0302.JPG

    So the payload is the weight of the bait.

    I am trying to combine the two and make a bait boat look nice, rather than a black rectangle...

    I got my 2ft length from this bait boat which is 50cm x 35cm dimensionally. Clearly, I cannot simply pick dimensions from one design and put them in another :(

    I hope this helps?
     
  6. OzFred
    Joined: Nov 2015
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    OzFred Senior Member

    Fit a bow thruster.

    You'll get 3 litre displacement from a half section of a 60cm tube with a 11.2cm diameter. That's going to be a very fat hull, even if split into 3.
     
  7. Doug Lord
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    Doug Lord Flight Ready

    =================================
    To get the shape close to that in the video* and still carry almost 7 lb you'll probably need at least 55"(1.4m) length. That would be a fairly high performance hull-do you need performance in a bait boat? If I remember correctly those waterjets are pretty expensive-sure you need them? You could use twin"normal" props with reverse and pivot the boat easily -even a barge shape.

    *too bad there's no sound...
     
  8. ayouden
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    ayouden Junior Member

    My original idea was to use props, as done in the boat in the video.

    However, with the fishing lakes being quite weedy, the chance of the props getting caught would be quite high. Or that's my view anyway...

    The water jets are around £30.00-£40.00 for a 40mm (large) jet.

    For the ease of use and application, this seems to be the better choice.

    From what I can gather, I might need to work out how big my Hull needs to be for such a high payload!

    I thought Trimaran due to the stability far than monohull...
     
  9. messabout
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    messabout Senior Member

    The shape that you have shown in Delftship is probably not going to be more stable than a simple flat bottomed boat of conventional design. If stability is your aim then the amas need to be farther from the center line. The subject boat will have excessive wetted surface and will require more thrust than a conventional boat.

    The boat that you have drawn is "sexy" and that is what it has to recommend it over ordinary skiffs, not much else. Perhaps I am being too critical and also there might be some conceptual details that I do not understand. Please explain in more detail.
     
  10. ayouden
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    ayouden Junior Member

    The main reasoning behind the trimaran design was to keep the boat from rolling side to side.

    When you mention the conventional boat hull, are you referring to a modified V hull design, or something else?

    Efficiency and speed aren't critical with this application.
     
  11. Rurudyne
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    Rurudyne Senior Member

    Given that speed isn't necessary, if you really need maneuverability, have you considered what I called a midwheel, a multihull take on a sidewheel paddlewheel boat? It is essentially a stabalized monohull/trimaran where the sidewheels are between central hull and the amas. With differential steering sidewheel boats can very maneuverable, especially if the wheels are independently driven so one can be in reverse while the other is forward.

    A stabalized monohull puts much more of its displacement into the central hull than a trimaran does so the movements tend to be both larger and slower ... but that is mainly a comfort issue so a conventional tri-toon type craft may be more on the mark.

    There's a sort of "sketch" I made with DelftShip in my gallery that may help illustrate the idea.
     

  12. Magnus W
    Joined: Nov 2017
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    Magnus W Junior Member

    Jets are normally very sensitive to debris and I would assume that that would be the case for rc-sized versions too. I haven't heard an argument for a jet drive being based on the assumption that it would work better in waters with lots of debris in it. Shallow draft, manoeuvrability, safety for persons in the water are more common.

    Another downside to jets are that they aren't easy to clean once you do get something stuck in there. A prop, perhaps with an easily removable shroud, is way more accessible.

    Since speed and efficiency aren't your main concern, have you considered shrouded thrust fans (like on a hovercraft)? A twin setup should provide good control, perhaps ad a bow (and stern) thruster if necessary, and you will have no issues with whatever's in the water.
     
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