Lego method for hull design

Ok, this might seem a bit ridiculous, but please bear with me. I’ve been thinking about methods that could accelerate the construction of prototype hulls. It seems to me that whilst there are a variety of tools for the 3D design of hulls (DelftShip, Autocad Inventor etc), without a CNC machine, converting 3D designs into a physical form is a time consuming process. It also appears to be relatively difficult to make minor modifications once the construction process has started. After some (perhaps not enough) thought, I’m currently considering trialling a Lego/plasticine method that I think might be a viable alternative to the balsa, and foam block methods typically used.

This is the process that I am considering:

Step 1: Build the basic shape of the hull in Lego;
Step 2: Cover the hull with plasticine to provide a smooth surface;
Step 3: Cover the plasticine with something like cling wrap;
Step 4: Use the shape as a male mould;
Step 5: Remove hull from mould (or if doesn’t come off easily, deconstruct the mould from the inside).

It seems to me that the potential advantages of this method include:

  • fast construction;
  • easy modification of the design in the physical form;
  • easy production of symmetrical hulls;
  • materials (blocks) can be re-used;
  • Lego modelling software available;
  • construction plans easily distributed;
  • complex shapes possible as mould can be removed from the inside;

Before I make a fairly significant investment in Lego blocks I’d appreciate some feedback (and constructive criticism). Has anyone seen a similar method used before?

I can see myself doing this up to the point where you have to give a smooth and regular surface to the plasticine in order to end with one continuous curve. Not sure how we can sand or “press” the plasticine that evenly.

Well, unless “plasticine” here don’t refers to the play toy kind for kids that I had in mind, but something else. Maybe some plumber paste or clay would do the trick.

Just a thought.


Hello Sylvian,

I’ve tested the plasticine (minus the Lego) part of this method on a deck and it worked surprisingly well. I used plasticine purloined from my kids. Unlike the plasticine I remember, it was less brittle and easier to work. In place of sanding, “smearing” seemed to work quite well to get a continuous curve.


Hi Mij,
before making any comment, I went checking the Lego Brick modulus and found out that is about 8x8x9.6mm.
This means that any curve you like to make, you need to play within this modulus. This correspond to 1/4 of a brick.

With relative large forms like a real “12foot dinghy”, the minimal brick dimension may be not a problem.

Instead with our model dimensions the compilation of bricks will produce a very irregular form.
The plasticine thickness will vary from one brick to the adjacent one.
To better understand, I just simulated the brick combinations for two different bulkhead shadows size and limited to a 2D vision, 3D vision will be further complicated :

I do not knows if I have well understood your idea, but for me it will more complicated and work demanding effort and money than the classical construction and /or foam construction.
Yellow surface = plasticine
Hope to be wrong ! for you

Hello Claudio,

Very nice analysis, you certainly understand my idea. I take your point regarding the limitations of a set block size and the potential for irregular forms. However, I don’t think that the situation is quite as bad as your example suggests. I had imagined using the smallest block as the base element. These are 7.8x7.8x3.2 mm. I’ve recreated a similar example using both the larger and smaller elements:

The modulus remains the same, but less plasticine is required and the thickness is more even. Does having different thicknesses of plasticine present a significant problem?

As for the cost, the initial setup would be costly, but all the parts should be reusable. In the long-term it may quite cost effective?

Whether or not Lego is a suitable tool, I think that this approach has some potential - a reusable toolkit for the construction of hull prototypes based on small linkable elements. The advantage of lego is that it is available off the shelf.


sheesh I have 20lbsof legos… just sitting around…better get to work…

in stead of pasticine what about drywall mud? i think a lot wold would need to go into keeping the shape. still need to have some sort of “form” to ensure proper shape from one station to the next…

i think the time spent tyring to build and shape could be better spent on foam…


Definitely time to put that Lego to good use (and utilise all those skills developed in childhood).

The advantage I see over foam is that you can put material on as well as take it off. Of course, this is irrelevant if you are designing in CAD and having the foam machined.

Some sort of clay might work, but I’m thinking of making a whole base of Lego, rather thane just stations, so I don’t anticipate that I will need all that much plasticine. Of course, I’m thinking about smaller hulls than you usually work with, so not as much lego required. Perhaps bigger hulls need Duplo?


Interesting discussion… watching with interest. I have not built a hull from scratch so I know nothing…

However, it occurs to me that the Lego will have some degree of flex - would it need some sort of stiffener or be fastened to a base somehow? Is rigidity an issue - and if so, also an issue with foam?

Hello Claudio,

I have tried to visualise how this technique would work by drawing how it might look when applied to a known boat. I hope you forgive me for choosing you Footy Esterel.


Hello mr,

I think that a base will be necessary. I imagine building on a flat Lego sheet, with the sheet representing the deck. My experience with foam is limited to small hulls, where flex certainly isn’t an issue.


although you may found a reasonable compromise to assemble the mini bricks as such to follow the hull shape in 3D, a lot of irregularities will deviate from the real form. No reference line will be available except the deck line.
You may need to have all intermediated shadows and put the bricks in between and probably without matching the linear distances since the brick have their standard dimensions unless the shadows are separated with a multiple of the brick size.

At this point the foam material is much cheaper and can be shaped as you like to meet the shadow relative distances.

Of course also the houses are often built with bricks, but only one 2D form is then required and doors and windows obey to the brick size,but this is another story !

This is my point of view, at glance



I think that I am going to have to concede that this method is not going to be as straightforward as I had hoped. The sketch of your Footy supports your arguments and shows that quite a bit of plasticine (or clay) would be required to match the shape of the hull. There appear to be two options, use a lot of plasticine, or let the geometry of the Lego dictate elements of the hull design. Neither is ideal, but the former may be ok?

I don’t entirely agree that there will not be a reference line. One advantage of using Lego is that it would be easy to produce external guides and inverse shadows - for example see below:

Before rejecting this idea I will test it on a small scale. The benefits of being able to use both additive and subtractive methods, whilst avoiding sanding seem worth pursuing.


the possibility to use subsequent independent horizontal planes may offer a possible approach.
I went checking the prices of the bricks and I was really surprised how much they cost see:
A standard brick for 0.25$, a construction box with 405 pieces for 40$
Assume, as an example, a deck plane of 100cm x 20cm, you may end up with about 520 pieces !! I let you imagine the rest !

Going back to the sequential horizontal planes technique, I’m sure that the use of plywood or foam planes is the cheapest and most precise method. Shadow and stripes is very good and pleasant.
I used the very ancient Bread and Butter technique also for the Esterel footy Master as well and, since long, for the leads bulb construction to avoid dangerous melting operations.
Ordinary plywood is not very expensive, than you have the choice for the thickness as function of the amount of rasp work you intend to carry on in accordance with the step dimensions. Of course is better to invest in a band saw.
B & B is a very fast construction too : here an example of :

With the price for a single layer of Lego bricks you get the full wood you need. Foam is also a cheap method while more delicate to manipulate.

With my personal argumentations and suggestions I do not intend, of course, to modify your desired constructional approach.

the only thing you have to loose jim is time… in the mater of a few weeks you can build an entire model boat… one of my joys in the model world. build it. if you don’t like it. build it again…

slowly getting the nerve up to build a canoe or kayak…

Claudio and Marc,

Thanks for the advice, all the points you make are good. However, I’m intrigued to see how this method might work so I might go ahead and try it any way.

As I find myself in need of a slightly larger (and better performing) trimaran, I thought that I might start with a 65M main hull. I’ve had a go at a preliminary design using Bricksmith (LEGO CAD modelling freeeware) and the results are shown in the attached figure. I’m making lots of guesses, in particular the DSPL, so more detail will be required. Any suggestions regarding the technique or hull design would be appreciated.


Hi Jim,
have you calculated the bricks you need.and costs ?
My rough estimation more than 13000 pieces.
Good luck !


Sorry, I didn’t provide sufficient information. For the design I used the smallest brick as this gave the maximum flexibility in varying the shape. It also provided a simple way of estimating displacement (simply by using the software to count the number of bricks in each layer). When I come to making it I will use a combination of larger LEGO bricks and plates. By using plates the structure will be hollow, which in combination with the use of larger bricks will reduce the total number of bricks significantly.


As a preliminary test of this method I’ve applied it to the bow section of the hull (ca. 150 mm section). The pictures below show the progress so far. To give an indication of the time involved:

Assembly of the LEGO structure - 20 mins;
Application of plasticine - 10 mins;
Smoothing of plasticine - 20 mins.

So far the method seems to work nicely. Smoothing the plasticine is quite different to sanding. I found that using a silicone spatula worked quite well.

Next: application of glass fiber/epoxy.

looks neat…

Great idea, but being a Lego fan I would suggest using mega blocks that’s because when your all done u can throw it in the trash. Mega blocks suck