The Little 3D-Printed Tugboat That Could

If you’ve ever spent time watching the goings-on at a seaport, you must have seen tugboats at work: those little boats that push, pull and nudge enormous cargo ships through tight corners in the harbor. They manage to do that thanks to hugely powerful engines sitting inside their relatively small hulls; their power-to-tonnage ratio can be ten times that of most commercial ships.

One hardware hacker who enjoys building similarly-overpowered machinery is [Luis Marx], and it might not come as a surprise that his latest project is an actual tugboat. Living on the shores of Lake Constance in southern Germany, [Luis] likes to spend time on the water, but got fed up with the chore of paddling. Local regulations restrict the use of outboard motors but allow the use of R/C model boats; therefore, building an R/C tugboat to move yourself around the lake should be perfectly legal.

While we’re not sure if the Lake Constance Police will follow the same reasoning, [Luis]’s model tugboat is a wonderful piece of engineering. With a design inspired by 3DBenchy, the standard 3D printer benchmark that probably anyone with a 3D printer has printed at some point, it took about 30 hours to create the parts plus a generous helping of epoxy resin to make it all waterproof. A beefy lithium-ion battery pack drives two brush-less DC motors designed for racing drones, which together can put out nearly one kilowatt of power.

That, unfortunately, turned out to be way more than the little boat could handle: any attempt at using it simply caused it to leap out of the water and land on its back. Setting the motor controller to around 50% made it much more controllable, yet still strong enough to move [Luis] around on his standup paddle board. The boat is controlled through a custom-made handheld R/C controller that communicates with the ESP8266 inside the boat through WiFi. With no rudder, left-right control is effected by simply reducing the power of one motor by half.

A fully-charged battery pack provides enough juice for about 40 minutes of tugging, so it’s probably a good idea to bring along paddles in any case. Unless, of course, you’ve also got a solar-powered autonomous tugboat ready to come to your rescue.

24 thoughts on “The Little 3D-Printed Tugboat That Could

  1. Excellent project.

    I suppose the motors work under water – after all the magnet wire is isolated. How long would the bearings last? I would imagine parts would start to rust after a while.

    1. I imagine the bearing life would depend entirely on the type and quality of their seals, which varies heavily between manufacturers. A little surface rust on the exposed body woudn’t do anything, it’s only once the water found its way into the balls and races that you’d have issues. Looking at that motor, though, it does look like the bearings are only shielded, so that might not take long at all.

  2. He must have been pretty confident about it, with all the stuff he brought with him on the journey that could have gone overboard.
    He didn’t mention it in the video, but I would hope he made the controller waterproof as well.

  3. Maybe he already tried this, but having counter-rotating props should help a lot with stable full power operation.
    WWII aircraft had a lot of issues with prop torque and did some interesting experiments with counter-rotation, including which directions of counter-rotation worked better with specific airframes, and the much more complicated coaxial counter-rotating props that still are used on the primary Soviet bombers.

    1. That’s contra-rotating, counter-rotating simply means that two engines rotate in the opposite direction from one another.

      Contra-rotation necessarily adds a massive amount of complication, whether it be a gearbox or concentric shafts from separate motors.

      1. Contra-rotating can also be a lot more efficient, if you design the props together, so the first prop adds swirl and the second removes it – less energy into making air swirl means more energy into pushing it backwards.

        But most attempts from drone hobbyists stick two normal props in line, and instead see a massive drop in efficiency, because the angle of airflow into the second prop is completely different from what it would see in free air.

        Also contra-rotating props get extremely loud from the wakes interacting

  4. Since its tethered, he could double the tether to keep the larger battery on his board… also I hope he brought paddles with him to row back to land, seeing in the end of the video where his benchy propellers got tangled up with seaweed… 😅

  5. I hope the local fun police are not nearly as big of jerks as the paddle boat workers at the pond i used to use my RC sailboat in. They told me I couldn’t use my silent non motorized boat. When I informed them I looked at the rules and yes I can, he insisted it was a rule. So I said show me. Then he threatens to call the ranger and I said please do. I’ll wait. Maybe he can find this mystery rule. So eventually I had a letter from the parks department saying I could, which I never got the chance to shove down his stupid face because I moved. Wait, oh this is Arby’s? I’ll show myself out.

  6. my state requires registration of all motorized craft, sailboat, or houseboat over 12 feet in length….
    This tugs got me wondering what the state police would think if I had this….or a robojetski to tow my pirogue

  7. Very novel approach. I recently bought a 23″ tugboat to retrieve my other electric RC models by dragging a line with 2″ fishing floats attached. I circle the stranded model & the line on the water snags on a prop or rudder so that I can tow the errant vessel back to me. I’m building several other boats & using brushless drone motors with 3.17 mm shafts connected via universal joints to shaft-Stuffing box-prop combinations also purchased from amazon for $14-19. I use NIMH battery packs as the chargers are simple, inexpensive, uncomplicated to use. My 2.4 Ghz RC controllers are about $48 also from amazon. I forget what I paid for the drone motors. They come with 40 Amp brushless ESCs ( electronic speed controls). I steer 2 ways, by differential thrust or by rudder which i prefer. My newest vessels use jet ski technology, hobby water jet propulsion with steerable nozzles. These are best after early July as the City of Toronto doesn’t use herbicides anymore to keep weeds down in our 3 model boating ponds.

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