4

I enjoy making Power Functions-controlled boats to race (in water) in various LEGO convention competitions (which require 100% genuine LEGO pieces).

Usually, these boats end up being paddle boats, because of how inefficient all the LEGO propellers are. Supposedly Propeller 2 Blade Twisted (4745) is actually the most-efficiently shaped LEGO water propeller.

Propeller 2 Blade Twisted part image

There are a number of problems with this propeller.

  • The blade are thick.
  • There is no good way to attack an axle to it.
  • The shape of the blades is sub-optimal.
  • It's on the small side.

Is there a way to build a more-efficient one, out of several pieces?

5

The LEGO RC boat by Slewentogzz claims to have a top speed of 3 km/h, it uses a custom propellor built out of Technic parts.

The actual rudder parts appear to be Technic Panels #87080 and #87086. These panels are very common and are available in over 60 sets.

There are two more parts in a similar design (#64683 and #64391, they are one stud longer each so you can make a slightly larger propellor.

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Images: Slewentogzz Lego Creations

Video: "Lego RC Boat with custom built propeller (3,0 km/h!)"

  • I've tried the propeller. Unfortunately, I found it still under-performs paddle wheel designs. Not a bad suggestion for an alternative propeller design though! – Alexander O'Mara Dec 13 '17 at 22:40
  • In theory, I don't think a paddle wheel can be as efficient as a propellor. – Ambo100 Dec 13 '17 at 22:47
  • Yeah, that's my understanding too... But in practice LEGO doesn't make a proper water propeller. – Alexander O'Mara Dec 13 '17 at 23:51
  • 2
    @Ambo100, a properly shaped propeller is far more efficient than a paddle wheel because it takes advantage of hydrodynamic lift rather than merely direct displacement of the water. The hard part is getting the shape right -- if you don't have the right curves to produce lift, you're wasting most of your energy just churning the water. – Mark Dec 14 '17 at 6:34
1

Rather than making your own propeller with piece- which might break under the stress of water- i recommend using a different propeller like:

More propellers: https://www.brickowl.com/catalog/lego-parts/vehicle/propeller

  • 1
    As far as I can tell, and according to my one link, these propellers are actually worse than the yellow one pictured due to how small the blades are and how shallow the blade are pitched. – Alexander O'Mara Dec 13 '17 at 22:42

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