Unique 5' remote control trimaran, thoughts and advice

Discussion in 'Multihulls' started by wizzwas, Sep 18, 2017.

  1. wizzwas
    Joined: Sep 2017
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    wizzwas Junior Member

    I'll start by saying I am a newbie here and to all this boat building, so don't know too much technical stuff. Hello!

    I am doing some research for the latest side project I'm doing at work. As I said, I'm not an expert on any of this stuff really, but I do have an interest in it all and I'm fairly handy.

    Basically we want a remote camera boat. A remote control boat with a remote television camera mounted on the top.
    I intend to spec' it for a big camera that weighs around 20kg(basketball-ish size), although it will probably be something lighter most of the time, plus the extra gubbins that go with it and other boat internals (motors, batteries, transmitters etc.). So all in all it would be a 30kg maximum payload.
    The 20kg of the camera will be about 50-60cm above the water, and higher for lighter payloads.

    My current thinking is it should be around 150cm (5') long and 100cm or so wide. It can't be too big as it needs to be as discreet as possible, and not too much draft (30cm?) as it will likely be launched from the side of shallow lakes. I thought about buying 3 model boat hulls, one big and two smaller hulls, and making the members to attach it all. But as most model hulls don't come with maximum weight capacity there's a bit of a question mark. Tempted to make the hulls myself from fibreglass going on basic hull designs but again, don't really know what weights different sizes/designs can take. And I'm just presuming a trimaran would be a better choice than a catamaran for this project?
    A complete carbon fibre sleek design would be the dream though.

    I'd be really appreciative of any thoughts, advice, pictures, hull sizes/designs... anything you guys care to add.
    And don't say it can't be done, we already have a smaller 1m long single hull RC camera boat!
     
  2. hump101
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    hump101 Senior Member

    The hullform will be based on what you want to achieve with it. If it is only ever going to move slowly then any shape with sufficient static stability will do, a barge shape for example. If you need any speed then a catamaran would be optimal. A trimaran doesn't offer any additional stability and will just have higher resistance in such a short hull, and cost more to make.

    You might want to tune the stability stiffness to match your gimbal capabilities, but most modern kit will outperform the hull shape regardless of form. This is really only an issue if endurance on batteries is a problem.

    Displacing 40kg at this length is easy, 10cm draft, 20cm beam fairly full hulls would achieve this, no need for 30cm draft.

    We make RC models of this size for prototyping, they work very well so you wouldn't have any issues with this. Building in carbon makes sense, the cost will be trivial compared to the kit you're mounting on it, and you'll be grateful every time you have to lift it! Just cut some foam to shape and vacbag some skins onto it, and you're done.
     
  3. wizzwas
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    wizzwas Junior Member

    Excellent advice, cheers. Knew this was the right place to come to. I got another great reply but it hasn't shown up here for some reason.

    "Displacing 40kg at this length is easy"... fills me with confidence too!

    Now does anyone have any pointers to the hull shape? I don't think we will be going too fast, up to about 3 knots maybe.
    Something fairly basic would be ideal as I'm probably going to be building the whole thing myself. I plan on having a dual motor/no rudder setup, one in each hull. I guess it should do the job, even if it may be a little difficult to manoeuvre.
     
  4. hump101
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    hump101 Senior Member

    At 3kts the shape doesn't matter that much. Depending what you are filming you could choose something that minimises wake if this would disturb your subject. For a typical cat that has a width at least half it's length then two motors will be fine for manoeuvring, just a bit limiting if you want to get nice smooth turns at speed for panning shots, but a bit of practice and it will be fine. There are electric outboards available at this scale that would give you steering and propulsion in a single package that you can change out for repair in the field with spare units. these really simplify the installation.
     
  5. rwatson
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    rwatson Senior Member

    There has been some great advice here, on an interesting topic.

    Just a couple of points here that might be helpful, based on model building experience.

    Keeping the hull light to save batteries would be a helpful thing, but also a trick I eventually found to make the hull easily. Contact you local fiberglass shop, and buy a sheet of 4mm high density foam to build the hull from, before you glass it on the outside.

    Carbon fibre and other exotic material are a complete waste of time and money. All you need is some light glass material. If you put a layer on the inside and outside of the foam, you will end up with a hull you can almost stand on, and be the lightest possible.

    You can use quality automotive touch up paints and fillers to make the outside finish.

    Just for possible interest, I have attached a couple of photos of the build process, and a link to a Youtube Video showing remote control of a camera inside the boat that might give you some ideas.

    Have fun with the project, and good luck.

     

    Attached Files:

  6. wizzwas
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    wizzwas Junior Member

    Nice. The outboard motors is interesting, I'll have a look at them. On that note I was looking at motors and props the other day, I'm not too sure what to go for. I guess the same applies if I went for outboard. I imagined something like a decent 1/10th scale(car) motor with a big sized prop, say 100mm. There isn't too much out there on heavy boats this scale. Does anyone have any thoughts on that?

    I'm also upping my weight to about 45-50kg, my payload and internals come to around 34kg and I imagine the weight of the boat will exceed 6kg.

    Interesting about the foam, I'll have a look at doing that too. Very inventive with the camera and trigger on your boat too. Let's just say with the camera that's going on this boat, sinking is not an option... at all.

    Is there anywhere that has examples of these hulls, I suppose one that minimises wake would be handy. Just pictures or something I can vaguely copy from. I think I'll make a foam/wood plug and then a mould and the hull from fibreglass to start with and go on to do carbon fibre if I'm happy with it.
    The next thing I'm curious about is how to make an enclosed hull and what to make the crossbeams from?
     
  7. rwatson
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    rwatson Senior Member

    Yeah, the power setup is a deal to think about.
    Electric outboards are a bit scarce, and given a preference I would go for inboard just for ease of installation. Most model shops will have brass tubes, props etc. and electric motors.

    IF you use foam and glass, you MIGHT be lucky to get the boat to come in under 20kg. Its amazing how the weight grows. That boat of mine was about 4 feet, and it was built to scale weight, and still came in at 12 kilos for the hull alone.

    If top speed performance isn't an issue, you don't need to worry too much about the hull shape, just make sure it has enough buoyancy to support 50k, and hull rocker to allow for maneuverability.

    The beams will be easy. Just get a 2 or 3 aluminium tubes from the local hardware (say 1.5" - 2") . If you can't bend them with your bare hands, they will be strong enough. Being a tube, you can make them insert into the two hulls, to make storage and transportation easier.

    As for sealed decks, build the two hulls open, put some beams (wood or aluminium) across the top (1" deep, .5" wide) , and epoxy some of that foam sheet across from side to side, epoxying it to the beams and hull edges, and weigh them in place until the epoxy goes off.. Then you cover the top of the foam with glass and epoxy That should be plenty strong enough. You could always glass one side ( the underside) of the deck sheets before epoxying it down, for extra strength, but it will be added weight.
    If you have any areas that are suitable, you can cut weight saving holes in the deck and cover them with light plastic film, waterproof and lightweight.

    If you are smart, you will make the beams where you need to screw down you camera gear.

    DONT be tempted to use plywood - the weight shoots Waaay Up V quickly. Balsawood is OK, but you run the risk of it getting wet and falling apart.
     
  8. hump101
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    hump101 Senior Member

    Not wanting to contradict Mr. Watson, but this is not a model boat, it doesn't have to look scale, and it's going to carry several thousands of dollars of camera kit, so flooding is not an option. I would use solid closed cell foam hulls (100 litres volume would weigh 3 kg) shaped with flat outsides to minimise wake, with 2 layers of 300g/sqm carbon skins vac bagged on (another 3kg) and carbon or alloy tubes to connect them (another 2 kg). That will produce a structure that will never sink, will sustain serious groundings or impact, and will be easy to move around when not in use. It can also be built rapidly and easily repaired. The cost of carbon for this would be under $100, so a trivial component of the total, but will save you 1kg over glass and be 5 times stronger. Everything (batteries, electronics, etc) mounted in sealed containers above the deck level so flooding, and hence loss of drive/control, is never a problem.

    Outboards are available from Graupner and others, along with props to suit. The outboard units give steering and reverse control, and can be made submersible easily, so reliable without leaking stern tubes, etc. They just bolt on, with three connector for power/reverse and one cable for steering, so installation/removal cannot be easier. Have a third one in the kit ready to go an you should never have to miss a days shooting. Bear in mind that most model kit is designed for high speeds, but will still function perfectly well for this application albeit with reduced efficiency. If you want fine control, then just fit smaller props, more thrust then fit bigger. The standard motors are far more powerful than this application requires, and you can change rpm with motor choice and battery cell count.
     
  9. rwatson
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    rwatson Senior Member

    Hmmm. Just a few points to consider for someone who has never built a large sized model boat:-

    1) "I am a newbie here and to all this boat building, so don't know too much technical stuff."


    "2 layers of 300g/sqm carbon skins vac bagged on"

    See a problem here ? The OP wont have a vacuum pump or want to spend a lot on the bagging materials, vacuum pump, pipes for vac bagging etc.
    Also, ever tried to wet out carbon by hand on sharp or compound curves, especially 300 gm cloth ? Its not easy, and by having to cut darts, you lose a huge percentage of the structural strength that the carbon is supposed to provide.

    2) "closed cell foam hulls (100 litres volume would weigh 3 kg) "
    Actually, it will be closer to 4 kilos. And since "Carbon will save you 1kg over glass " makes the difficulty of wetting out heavy carbon pretty pointless.

    "be built rapidly and easily repaired"
    No. Carving out a hull shape from foam is messy and difficult to make look good. Also, you have to fair the rough cut foam with heavier epoxy and "balloons", whereas high density foam sheet is already smooth on both sides and doesn't require nearly as much sanding.

    There is certainly value in placing expanding foam in the hull at strategic points for solid flotation, and even to assist structurally.

    3) "serious groundings or impact,"
    Um, how much impact do you think a ~60 kilo model boat with electrically driven 3 cm plastic props will produce ? If you are worried about getting run down by a full size outboard and dinghy, you are boating in the wrong place.

    4) "The outboard units give steering and reverse control,"
    Well sort of. Don't forget the steering is actually provided by servos (sold separately) and by Electronic Speed Controllers (also sold separately), which live inside the hull.

    The steering on outboards only works if the motor is turning. There may be an advantage to having separate rudders if you would like to take advantage of light wind or current drifting down on say, unsuspecting ducks. Certainly, I have needed to control drift into a suitable landing place when my battery went flat, and I had no power from the motor.

    Outboard units start from about $US120, and are just a standard brushless motor in a specially shaped plastic case. Separate quality brushless motors can be about a quarter of that. Also, if you find that you need to change power and size of electric engines, you won't be able to, as you need to stick to the plastic outboard case dimensions.

    A lot of design decisions are going to depend on the hull layout. Having outboards hanging off the stern with the associated cables and wires might be problematic, especially if its a trimaran with two skinny outer hulls.
     
  10. alan craig
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    alan craig Senior Member

    This project is getting bigger and the camera is getting bigger and more expensive. It might be much better to buy a small used sailing catamaran, remove the rig and fit a trolling motor. Dead easy to control the steering and power using radio control gear and almost nothing to build.
     
  11. hump101
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    hump101 Senior Member

    I can only respectfully disagree with Mr. Watson again. If the OP doesn't have vac bagging material then a quick trip to a local composite fabricator will net him all the materials he needs for free, they are pennies to anyone buying by the roll, as we do. He's in the UK, so lots of choices. He can buy a cheap eductor if he has air available, or borrow a pump, or use waterbags, anything will work well at this scale.

    I've wet out a lot of carbon, both around sharp corners and on compound curves. If the cloth is woven it easily accommodates the mild compounding on this shape, and no need for sharp corners, though they aren't an issue with a vac bag.

    Why would you use 40kg/cubic metre foam instead of 30kg? 30kg plus two layers of 300 cloth is just about enough to support walking on, so more than enough for this application.

    Carving foam is very easy using tools like a power plane and sanding pads. No need for any filling or fairing, ever, unless you make a cockup. Shaping these hulls would be no more than a few hours work, with another 2 hours for the skins spread over two days.

    My comment about serious grounding or impact is about the capacity of the structure I proposed, not necessarily what is required, but if you have to drag the boat over rocks to recover the gear, or it gets attacked by the creature you are filming, it is nice to know even if a bit gets chewed off it won't flood or sink.

    Model outboards have disproportionately large fins, so work well as rudders even when not running the propeller. Servo's can be sealed and mounted on top of the hulls, or inside the boxes with glands, or on the motors. No need to have any floodable spaces inside the hulls.

    I've no axe to grind with any path the OP chooses to take, but we've made a lot of models for testing and prototyping, and I would never have a floodable hull if it can be avoided. Model boats are great if you want to go model boating, but if you need it to be a tool for a different task, to protect expensive equipment, and to minimise manhours and downtime, it is a different set of criteria.
     
  12. wizzwas
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    wizzwas Junior Member

    To clarify, after the pointers, catamaran is clearly the better, easier and cheaper option, so I'll be going with that design.

    I was actually looking at 400gsm prepreg carbon fibre earlier to use for the hull, maybe something lighter on the outside. Although I'm thinking it could be easier to make a plug myself then give it to a pro to do, depending on how much it'd cost. Then again, I might do a hull in fibreglass first to see how well it works, then do a carbon version.

    Solid hull is probably the sensible option, but I imagined having it hollow and having a couple of O-ringed hatches/panels so I could house the boat batteries, the camera batteries (4x 1kg) and get to the motor setup. It would make battery swapping easier on a lakeside and it would keep the centre of gravity lower too.

    Outboards is a good idea, if things needed to be swapped out in the field. Might just be easier to do the dual motor, no rudder setup though.

    A fair suggestion Alan, but it needs to be small, as in around 1.5m long max. To be honest the price of the camera that it's being spec'd for, you could buy a nice second hand 90ft catamaran! So spending a bit of money on getting it right is probably going to be worth it.
     
  13. UpOnStands
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    UpOnStands Senior Member

  14. wizzwas
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    wizzwas Junior Member

    Interesting, I'll look into that truss. It at least gives me a few ideas. I have been thinking lately how best to make the crossbeams, I've added a picture of one of my initial sketches. Obviously I could just bolt some carbon fibre rods across to attach the hulls, but I'd like it to have some sort of designed element in there. I mean the crossbeams will have a camera plate attached in the middle and thats where most of the weight will be, up to around 25kg, so it needs to be something fairly substantial.
    upload_2017-10-31_20-49-41.png [​IMG]
     

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  15. UpOnStands
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    UpOnStands Senior Member

    You already have a 1m boat so some experience. What type of hull movement is best handled by this new bigger camera? Short jerky moves or long slow rolling motion?
    If the hulls are flat and full width at the DWL the draft is shallow but the boat is likely to bob strongly with small waves.
    If the hulls are narrow at the DWL the draft increases but is less susceptible to waves.
    With the CF truss you could easily create a modular camera mount.
     
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