Home > Watercraft > Trimaran


My second marine vessel, another multi-hulled boat. Features rotary propulsion system and makes use of the Lego RC unit. Also included: the Grim Reaper.


Completion date: 29/06/2011
Power: electric (RC unit)
Dimensions: length 96 studs / width 32 studs / height 32 studs (including propellers, not including antenna)
Weight: 1.756 kg
Displacement: 1.9 kg
Suspension: none
Propulsion: 2 x RC motor
Motors: 2 x RC, 1 x PF Medium

My second boat was intended to be larger, faster and radio-controlled, unlike the previous one which depended on easily lost IR link. I have finally managed to buy a Lego RC unit and RC handset – something I was looking for for years – and the new boat was a perfect opportunity to use it.

I was looking for larger displacement, so I have taken the four 50821 hulls from my previous boat, combined them back-to-back creating two very long and thin hulls, and added the 54100 hull in the center, where it increased the total displacement significantly. Eventually the boat was surprisingly heavy but it used less than half of its total displacement. You can notice on the video that the draught of the hulls is noticeably smaller than it was with my first boat.

The goal of the propulsion system was to provide high speed regardless of the direction – my first boat used two independent motors, which run work at full power only when going straight ahead.  This time I decided to use two RC motors, as they seemed better suited for the job, and the use of the RC unit guaranteed unleashing their full power. The two motors were combined into a single block, without being mechanically coupled. The block also included driveshafts and propellers, and was mounted at the back of the central hull and rotated left or right by a PF Medium motor and a single small linear actuator in order to make a turn. The propellers were the same as in my first boat: four 9-studs long propellers combined into two four-bladed units. Another difference was that the propellers were not protruding in the back this time, but they were fully enclosed within the block, with liftarms in front and behind them. I was hoping this would help against algae and that it would be generally robust. Luckily, there were no algae in the part of the lake where the boat was tested. As for the robustness, the Trimaran ran aground at least once, to the point where propellers hit the bottom, and it was able to reverse and get back to deep water without any help from the outside.

The propellers were driven from the RC motors’ slower outputs with 1:1 gear ratio.

I was toying with the idea of using the RC unit’s steering output to control some spring cannons, which would make the boat able to fire at targets. However, I decided that it’s crucial to secure the RC units against humidity and I wrapped it in a freezer bag along with part of the wires, which made using its steering input difficult. There was also no real place for cannons left once the crew was installed on the deck.

As for the aesthetics, I thought: why build another dull, plain boat when I can build the Terror of the Ducks and the Vessel of Pure Evil? So, I have prepared a large and diverse crew, including undead ninja, zombie sailor and the Grim Reaper himself, and added some decorative elements such as skulls, bones, wings and the unique Lego globe from the 4191 set.  It made people passing by give me weirdest looks (and that’s without them looking closely at the boat), but it clearly impressed the ducks.

The boat turned out slower than I expected, which could have resulted partially from its huge weight. Other than that, the propulsion system worked flawlessly, and the steering was very accurate. The RC unit proved to be a very good purchase as well, as I was able to make the boat go several meters away from the shore and roughly up to 10 meters away from me. I did not test the actual maximum range, but it was far greater than the range of the IR-based Power Functions system.

Finally, I have experimented a bit with both photos and the video. Photos of the crew were taken inside a light tent, on an acrylic sheet, hence the reflections below. The video was taken using telephoto lens with a polarizing filter on it. The filter did not work as expected, perhaps due to poor lighting conditions, and it made the image blurry when close to the maximum zoom. I decided not to use it any more.


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Categories: Watercraft Tags:
  1. Sariel
    May 19th, 2013 at 20:47 | #1


    May 19th, 2013 at 20:11 | #2

    A pracują na tym samym napięciu?

  3. Sariel
    May 19th, 2013 at 09:42 | #3

    Of course not. RC and PF are two completely different systems.

  4. gleipnir
    May 19th, 2013 at 07:58 | #4

    Is your controller is compatible with the current system PF

  5. Sariel
    May 18th, 2013 at 13:10 | #6

    What are catalogue numbers of rc transmiter and revicer?

  7. November 14th, 2011 at 18:27 | #7

    Hmmm… Thanks. when I said ‘can I have it’ I meant squiddsters rc unit but I’d be happy either way 😀

  8. Sariel
    November 14th, 2011 at 10:34 | #8

    It was worth it for me. As for you, you’re the master of your money 🙂

  9. November 14th, 2011 at 09:22 | #9

    can I have it? 😀

    Sariel: do you think the rc unit is worth it? It is shocklingly expensive. Also would you recommend getting some of those boat hulls? Awesome creation any way.

  10. Sariel
    August 30th, 2011 at 16:02 | #10

    No, I haven’t.

  11. August 30th, 2011 at 15:58 | #11

    just wondering

  12. Sariel
    August 30th, 2011 at 15:52 | #12

    And how is that related to Lego?

  13. August 30th, 2011 at 15:52 | #13

    sorry I ment boat and it being ably to shoot

  14. August 30th, 2011 at 15:51 | #14

    have you ever thought of attaching a Nerf gun to a tank

  15. Sariel
    August 9th, 2011 at 17:29 | #15

    Yes, I have. And I’m not interested.

  16. Ben
    August 9th, 2011 at 16:41 | #16

    Hi Sariel!
    Have you ever thought of having wheels on some of your boats? You know, like an amphibious vehicle (runs on land and in sea) ?


  17. Sariel
    July 14th, 2011 at 08:08 | #17

    My brain.

  18. xxx
    July 14th, 2011 at 08:04 | #18

    which programme do you use for planig your models?

  19. Sariel
    July 6th, 2011 at 19:53 | #19

    I don’t have these propellers and they cost a fortune. Also, a really fast Lego boat can be built with paddle wheels only, not propellers.

  20. Philipe
    July 6th, 2011 at 19:43 | #20

    Hello, Sariel.
    I’d like to suggest you to use propellers from the FLL Power Puzzle challenge wind turbines’. I’d like to ask you to build a faster boat, using gears and, if necessary, more motors. It would be really cool. =)

  21. sqiddster
    July 2nd, 2011 at 07:13 | #21

    Gee, Sariel, I would have given you my RC handset and base for free… seriously, I cannot think of a use for that at all… I never considered the increased range important in this mode of transport. Nice boat, anyway 😉

  22. Sariel
    July 1st, 2011 at 23:32 | #22

    Thanks, I’ll correct that 🙂

  23. Mike
    July 1st, 2011 at 20:17 | #23

    sorry… 😀 I just replied to my own comment not yours.. see, you’re inspiring people. 😀

  24. Tanner
    July 1st, 2011 at 20:02 | #24

    Disguise the boat as a duck!

  25. Gimba96
    July 1st, 2011 at 17:51 | #25

    Nice work!
    only one thing: I read in the desription that the boat has 2 medium motors on board, but in the model there’s only one:)

  26. Sariel
    July 1st, 2011 at 15:33 | #26

    I’m not really sure I’m still needed in this discussion.

  27. Mike
    July 1st, 2011 at 15:29 | #27

    try a sailing boat! you could have sails and adjust them with pf motors. and also power the steering blade with a pf motor.
    wicked idea, isn’t it?? 😀 pfff……

  28. Mike
    July 1st, 2011 at 15:24 | #28

    yeah well still the take up water and spray it on the deck… wherever you put them.

  29. Mike
    July 1st, 2011 at 15:23 | #29

    hmm. and what if you have two whhels at the sides, but move them very far back to the end of the boat?

  30. Mike
    July 1st, 2011 at 15:23 | #30

    next thing you know people’ll be asking you to build Titanic. 😀 😀 or HMS Hood.

  31. Sariel
    July 1st, 2011 at 15:17 | #31

    No, I don’t. Two paddle wheels are more likely, but the problem with these is that they soak the entire deck.

  32. Mike
    July 1st, 2011 at 15:13 | #32

    I haven’t even looked at the price… expensive? I have one.. man, that seaplane set was such a hit for me.. it was sitting up on the shelf at a newsstand (!) I was so happy when Í got it!
    Imagine.. the first two Lego universal joints in my life!!! 😀 😀
    Are you planning to make an old-school Mississippi boat with a single large treadwheel in the back? the hull might be a problem..

  33. Sariel
    July 1st, 2011 at 13:56 | #33

    Yes, I’ve seen these propellers but they’re kind of rare and expensive. From what I’ve seen, paddle wheels are the best solution for Lego boats, much better than any kind of propellers.

  34. Mike
    July 1st, 2011 at 13:41 | #34

    What if you try aero-propellers to propel the boat? Of course these 9-long ones would be too small for that.. You know what would be good for this? I have set, the old yellow seaplane, that had a huge realistic propeller! with 3 blades. the only drawback is: it cannot be drive fast, because it tends to start shaking and gets stuck.
    this is it, this would give enough power if you used two with two RC motors, but unfortunately they tend to get stuck.. maybe if the prop was by itself and you could pull it on an axle for yourself, and it was’t a complete assembly… this was not a good idea from LEgo, it’s hard to use it well.

  35. Sariel
    July 1st, 2011 at 11:41 | #35

    May i suggest watching the video?

  36. Roeland
    July 1st, 2011 at 11:36 | #36

    Great creation!! But I wondered, how does it steer?

  37. Sariel
    July 1st, 2011 at 08:01 | #37

    Thank you for these many, many comments. There are no more efficient Lego propellers, especially not these ridiculously small 3-studs wide ones. The really efficient solution would be to use paddle wheels, except that they will instantly soak the entire deck.

    For example: because I don’t have them and they cost a fortune. And because they’re almost larger than this boat.

  38. ACAC
    July 1st, 2011 at 06:02 | #38

    Nice to see some floating lego here. I’m another floating lego fan from the other side of the world.

    Half a year ago I made a similar attempt to use IR to power 2 XL PF motors in a prototype on the hull of a 7994 set. Here is my link (sorry some words in Chinese but most are English)


    This prototype has no aesthetic beauty but I just wanna share my more primitive way to power a floating lego. Thanks 😀

    P.S. RC is great!
    I used a primitive customer-made propeller made of slopes, but surprisingly it provides the needed power to go fwd/backwd and steer. Powerhouse are fixed at the back of the hull so steering is achieved thru different spins between the 2 motors (thus cannot steer on full speed).

    I figured out that due to small power provided from IR units, a 3X gearing up from the XL motor is an optimum gearing. Anything above that, water resistant will be too much for the motor.

    You might also try some primitive “cannons” like I did. Since this was just a prototype and I’m lazy, I simply copied the shooterbot design from 8547 and put it ON the ship. Basically it shoots out Zamor sphere in a Bomberman way (Bionicle parts are used). Of course using also PF motors to power the shooting mechanism will save more space.

  39. Kevin
    July 1st, 2011 at 05:39 | #39

    Make an amphibious vehicle! that would be the coolest thing ever!

  40. garson
    July 1st, 2011 at 03:31 | #40

    why dont you use the new propeller blades from the renewable energy add on set, since the blades are separate you could use as many as you like and create 5 or even 6 bladed props, set 9688

  41. Neal
    July 1st, 2011 at 02:28 | #41

    or perhaps you could create something with this: http://www.bricklink.com/catalogItem.asp?P=57585

  42. Neal
    July 1st, 2011 at 02:21 | #42


    These may perform better:
    Although they could do with being a larger diameter, but retaining the longer blade with a steep pitch angle.

  43. Neal
    July 1st, 2011 at 02:15 | #43

    The propellers are what are letting you down. You need a prop with a larger pitch angle, essentially a prop suited to marine applications, rather than an aeroplane prop. Does a marine style prop exist in lego?

    My wakeboard boat is direct drive inboard, attached to a V8. Gearing is fixed, other than forward and reverse. I can control the pull out of the water, speed onto plane, and top end speed by changing the prop.

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