Cheap heavy-duty RC tugboat

Discussion in 'Boat Design' started by Anelito, May 15, 2022.

  1. Anelito
    Joined: Aug 2018
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    Anelito Junior Member

    I would like to create a RC tugboat similar to this one to carry my kayak around but using cheap PVC tubes and a pair of BlueRobotics T200 thrusters. I was wondering if, considering the peculiar task of pulling a rather heavy payload (myself, ~60kg), a non hydrodynamic hull like a pipe could work.
    Going to the actual PVC tube, I've seen experiments using totally empty tubes and others with lead weight, what should be taken into consideration when choosing one of the two options?
  2. Skyak
    Joined: Jul 2012
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    Skyak Senior Member

    The drag of the hulls times the speed is the power cost. If your tug only operates at very slow speed there is less incentive to minimize drag.

    On the other hand, electric power is more costly, and the cost of making reasonably streamlined hulls is not much different from draggy ones. It shouldn't be too hard to calculate out how much that drag will cost you. If you don't calculate it out there is a good chance your tug wastes most of its energy moving itself instead of the kayak.

    I don't quite understand the application. If the tug is only used to tow the kayak and is carried by the kayak when not in use, why have hulls at all? Why not just have the thrusters mount to the kayak? Making streamlined hulls that are better than pipe is easy. Making those hulls full of batteries and the towing rig break down conveniently to fit in a kayak is hard.
  3. fallguy
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    fallguy Senior Member

    Need to better understand the use, range, intent, etc.

    Steering the tug would be harder than steering the kayak..
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  4. Squidly-Diddly
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    Squidly-Diddly Senior Member

    I'd bet a mid-level hacker could make an RC boat that would home on a location/direction with cheap GPS from spare old smart phone.

    I'm thinking a big PVC pipe big enough to house one or two small Group 51 batts. 10" Schedule 40 PVC Pipe 4004-100AB
    Pipe will make ends easy to build as cone or "factory" caps and/or reducers.
    Mostly submerged floating pipe hull that is "deck awash" might not make a comfy manned vessel but might be idea as RC unmanned tug.
  5. Skyak
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    Skyak Senior Member

    FWIW, a guy already made a little electric catamaran to test some ideas for autonomous craft. I mention it because (if I recall correctly) he used the same thrusters and was successful -and thus would be in a great position to help you. Specifically, he could measure the power consumption/speed at different loads. He also has simple 3D printed hulls you could work with.
    autonomous surface vessel | Boat Design Net
  6. Flotation
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    Flotation Senior Member

  7. messabout
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    messabout Senior Member

    Here is a tug that pulls a person in a kayak.
    PVC pipe not involved.
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  8. mitchgrunes
    Joined: Jul 2020
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    mitchgrunes Senior Member

    Great demo of some the things that can go wrong with an autonomous boat, even in an almost flatwater canal, in fair weather. :)

    No life jacket.
    No emergency paddle.
    What if clouds covered the sun?
    He's pretty trusting, putting all that electronics in salt water.
    Not sure it has multiple flotation volumes, so one little fishing hook...
    Other people got out of the way. Did someone think "hazard to navigation?"
    If he fell out, the tugboat might have pulled the kayak out of his reach.
    BTW, some people wouldn't call that a kayak.

    But I guess I'm being picky.

    I'm astonished that such a little solar cell array can drive even a very inefficiently shaped boat at moderate speed. Imagine if he had a nice sleek sea kayak, with the motor and drive mounted on the hull.

    Cool, regardless.
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  9. portacruise
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    portacruise Senior Member

    Seems to me that if you take the motor workings from the flooded blue robotics and run the Armature in a conventional air medium with ball bearings instead of an Armature submersed water medium, it will be more efficient.

    I guess I'm missing something, but I just don't see the tow system as any advantage over having the whole setup contained within just the kayak part. And the mechanical setup of the tow system has some serious disadvantages.

    The degree of automation that has been achieved is truly impressive though! I want one to mount on my float tube and other small boats, haha!
  10. mitchgrunes
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    mitchgrunes Senior Member

    Oops. I didn't think through what I said.

    The video shows mostly very benign conditions, where some people swim. Maybe life jackets, spare paddles, and a thin skin maybe single chamber inflatable boat that is more pool toy than vessel aren't as important, if he can swim to safety. Though it would still be more responsible to have a paddle to better avoid getting in other peoples' ways, and to give one better options if the tugboat fails.

    A long thin sea kayak may only be more efficient in a higher power & speed domain, and requires some skill to maneuver. Given the limitations of his very crude steering mechanism, a small tugboat connected by a line, and an extremely lightweight toy boat, may be reasonably efficient.

    In fact, the way he is using it, passive stability may matter more than picking a shape that minimizes drag.

    And it is amazing what modern advances in the cost and efficiency of solar cells and batteries makes possible.

    But let us try a crude example: cover most of the top deck of a touring or sea kayak with solar cells. E.g., 10-20 square feet of reasonably high efficiency, photovoltaic array, reasonably sunny day, mid-latitude, giving very roughly 8-10 watts/square foot, might give you 80-200 watts, very roughly what a small trolling motor might use at mid power. (I'm ignoring the efficiency of the electronics needed to step up and regulate the voltage; it might also be less power than that because your deck is fairly horizontal, not tilted towards the sun like a rooftop array.) Under suitably benign conditions, that should be enough to move it pretty well. Just make sure you come home while the sun is still reasonably high, or be prepared to paddle.

    Each of the two thrusters the o.p. mentioned has a maximum power draw of 390-645 watts, at 16-20 volts, according to

    T200 Thruster with Penetrator (BlueROV2 Spare)

    So the thrusters would be well below full power, on average, in that scenario.

    If human control is possible, I think an autonomous RC tugboat is too complicated and trouble prone - I would just attach the thruster(s) to the back. (Though I admit seaweed and algae could be a problem in some places.)

    Maybe it makes more sense to use your paddle and/or leans to steer, assuming you attach the thruster(s) to the back of your boat?

    Though I could be missing the whole point of what the o.p. wants to do - it hasn't been specified yet. Maybe the o.p. loves the whole idea of an autonomous boat. After all, for the most part, kayaks now are toys, not practical shipping vessels, and efficiency is sometimes irrelevant.

    Perhaps a bigger issue is keeping salt water, ideally any water, away from the electrical connections. So maybe learn how people make marine condition electrical connections.
    Last edited: May 22, 2022
  11. BlueBell
    Joined: May 2017
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    BlueBell . . . _ _ _ . . . _ _ _

    They encapsulate them in epoxy.
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  12. alan craig
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    alan craig Senior Member

    I made some hulls from 2m long x 200mm dia. PVC tubes to carry flexible solar panels and was to be towed behind my small boat which was rather unstable with the solar panels attached as a roof. The total length of the tubes was about 2.6m after adding foam "bullets" at each end. It took far too much work to carve, glue, wirecut and finish the bullets so I would not recommend this method, but I've also made stabilisers from 68mm rainwater downpipe and this is much easier because of the minimal work to finish the ends - if they have enough buoyancy for your purpose. I think rectangular section catamaran hulls from plywood would be much easier to make.
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