LEGO Technic RC Boats: Making a LEGO Boat That Floats and Drives
You can build a LEGO Technic RC boat, but you have to work around one big problem: LEGO motors and battery boxes aren’t waterproof. Some Technic sets float on their own, such as the 42105 catamaran, and builders motorise them with Powered Up motors and hubs or third-party controllers like BuWizz, keeping all electronics high and dry inside the hull. Propellers driven by axles that pass below the waterline push the boat, and extra floats or a sealed hull provide buoyancy.
By Kyle HilsonUpdated: October 20263 min read
What you need
| Part | Notes |
|---|---|
| Floating hull | Set with floats, sealed hull pieces, or a custom foam/printed hull |
| Motor(s) | Powered Up L/XL or third-party motors |
| Controller | Powered Up hub with app, or BuWizz-type controller |
| Propeller | LEGO propeller or 3D-printed prop on an axle |
| Rudder or differential steering | Servo motor or two motors |
Build steps
- Start with a hull that floats with weight; test it in a bathtub empty first.
- Mount motors and the hub as high as possible above the waterline.
- Run a drive axle down to a propeller below the waterline.
- Add a rudder driven by a servo motor, or use two props for differential steering.
- Add the battery box last and check the boat floats level and stable.
- Test in a bathtub before a pond.
Keeping water out
- Keep electronics well above the waterline.
- Use a plastic bag or box around the hub (leaving cables free).
- Add a splash deck over the electronics.
- Avoid waves and spray; run on calm water.
- Dry everything immediately after use.
Buoyancy
LEGO bricks are slightly denser than water, and open builds let water in, so most of the floating comes from sealed hull pieces, floats or a custom hull. Add floats on outriggers for stability, like a catamaran. If the boat sits too low, remove weight or add flotation. Hull principles are explained in how to build an RC boat hull.
Control options
LEGO Powered Up hubs connect to a phone app or a LEGO remote over Bluetooth. Third-party controllers like BuWizz offer more power and their own apps. Range over water is limited, so keep the boat close. LEGO RC basics for cars are in how to make a LEGO RC car.
Safety
Only run LEGO boats in shallow, calm water where you can easily reach them, such as a bathtub, paddling pool or the edge of a pond, and supervise children near water. A string tied to the boat makes retrieval easy.
Project ideas
Try a catamaran with two props and differential steering, a paddle steamer with LEGO paddle wheels, or a fast hydroplane with a high-power motor. Experimenting with hull shapes and props teaches real boat design.
Take photos of your build as you go so you can rebuild it quickly if it needs to come apart to dry.
Making it faster
Speed comes from a light hull that planes, a powerful motor and an efficient prop. Builders use higher-power third-party motors and controllers, gear the propeller up, and 3D-print props that suit the motor. A long, narrow hull or a catamaran layout with less water contact is faster than a wide, flat one. Test changes one at a time and watch for water getting into the electronics as speed rises.
FAQ
Can LEGO boats float?
Some sets float; others need floats or a sealed hull.
Are LEGO motors waterproof?
No, keep them dry and above the waterline.
How do I control a LEGO boat?
With a Powered Up hub and app/remote or a third-party controller.
Where should I run it?
In shallow, calm water within reach.
More on this topic: the complete RC Boats guide covers the basics behind this article.
About 20 years in RC. Mostly boats in the NAVIGA Mini Eco Expert class, with many self-made parts; also a King Motor Baja 5B, a home-built electric plane, home-built nitro planes he has flown, and an RC helicopter. More about SwellRC
