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Is it possible to build a boat out of LEGO bricks? I appreciate you couldn't make it watertight but would a LEGO boat float by itself due to the buoyancy of the bricks themselves?

Pictures of any home-made floating constructions would be really interesting.

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The rowboat from many Pirate sets is known to float, along with a couple of minifigs, treasure and other elements on board. –  BoltClock Oct 25 '11 at 21:00
    
Could you use cling film (plastic wrap in the US?) as a seal between the bottom layer of bricks? –  Umber Ferrule Oct 25 '11 at 21:08
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@UmberFerrule Gluing Lego?!?! –  fredley Oct 25 '11 at 21:11
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Oh dear! Have I blasphemed?! ;) –  Umber Ferrule Oct 25 '11 at 21:16
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Lego boats like the ones shown below float, not because the bricks are buoyant, but because the model displaces water. –  Robert Harvey Nov 2 '11 at 20:35

14 Answers 14

up vote 44 down vote accepted

The plastic is a bit heavier than water and should sink, however in practice I have experienced that 2x4 bricks (and the like) have a tendency to trap air inside them and actually float rather well. It probably isn't failsafe, however for shorter periods of time (like a half to a full hour) would probably work fine. (I haven't actually tested the time it could stay afloat, I'm trying it out now. When my small mini-boat has sunk, I will add the time here.)

Update:

24 hours have passed, it is still floating.

enter image description here

It sunk about 1mm compared to the beginning, but nothing of importance. However while I did push it around from time to time, it was still in still water and stationary most of the time. How it will perform during play is unknown.

enter image description here

Notice how the internal structure of the bricks causes the air to be trapped inside them.

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11  
+1 for actual experimental data –  Friend Of George Nov 8 '11 at 22:05
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This should be the approved answer! –  J. Pablo Fernández Dec 9 '11 at 10:48
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+1 For underwater photo awsomeness! –  Ricibob Dec 9 '11 at 11:41

A few years back there was this solid single-piece hulled police boat which would float. enter image description here

There was also a small red boat (pre-2000) that came with part of a pirate set (I believe, anyway) enter image description here

As for building a boat from scratch...no. It tended to capsise then sink (somewhat impressively). Place 2x 4x2 bricks on another and place in water, they only float on their side. I expect this is down to a center of gravity but I'm not a sciencey type so I can't confirm for sure.

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There is also a brown variant of this red boat. –  Paŭlo Ebermann Oct 25 '11 at 21:14
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In fact, it comes in more than just two colors. Probably four or so (blue and black?). –  BoltClock Oct 25 '11 at 21:28
    
@PaŭloEbermann: The brown variant is actually more popular. –  JavaAndCSharp Oct 26 '11 at 0:13
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There are several other floating boat hulls (or small boat, inflatable boat, canoe...). Maybe it's worth mentioning that some of them are are in many pieces (peeron.com/cgi-bin/invcgis/…). –  Joel Cohen Nov 4 '11 at 18:39
    
Yup, I have one red and one brown of the boat shown above and they came with a 1990's pirate set. Don't remember which one though. –  PaulG Oct 5 at 6:07

i had a police-boat when i was a child that had a one-piece-body, so it was watertight and able to swim:

lego police boat

there are some other LEGO-boats with similar bodys (even some bigger ones) that should also be able to swim.

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My brother had that set as well. The body was actually three pieces, not one -- front third, middle third, back third. But each third was watertight and buoyant. –  Joe White Nov 13 '11 at 1:14
    
It's actually a three-piece hull: bow, stern, and.. uh.. middle. My brother and I had two of these and one fire boat. Made a great trimaran. –  gev Aug 30 at 19:45

My kids had Captain Redbeard's Pirate Ship - it certainly floated in the bathtub!

Captain Redbeard's Pirate Ship

I believe many of the other Lego pirate ships could float, particularly if they had molded single piece hulls - see this list.

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In addition of the various boat hulls, you can use pneumatic tanks for extra buoyancy.

If you want to motorize your boat, keep in mind that means extra weight, which has to be countered in some way.

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There is another not mentioned way to achieve flotation. My kid discovered it today with his "water bat": surface tension. The long flat wings did the trick : ) It is not exactly due to the buoyancy of the bricks themselves as wanted in the question, but might help as a complement.

Water bat

For more on the Physics underlying: Surface tension

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For a very small "boat" - something like a 4x8 plate with 1x8 and 1x2 brick sides it might stay afloat for a short amount of time before the leakage takes it down. For larger stuff, LEGO is just too heavy when you get in to building the necessary structure for a real boat.

There were some sealed-hull boat sets I remember from childhood that were designed to float, so using the special parts from them would make it possible.

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Already a correct answer accepted, but... the original question seems to be "do Lego bricks float by themselves?"

Most Lego bricks are made of ABS plastic which has a specific gravity greater than 1 (but only slightly). So, they are heavier than water and will not float naturally. You can get small bricks to float initially since small bubbles cling to their surface, but they will all sink eventually.

Since ABS isn't affected by salt water - it might be possible to increase the salinity of the water to a point where the bricks naturally float (would need to be higher concentration than sea water...)

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Whilst a solid block of ABS would sink, LEGO bricks are hollow. The issue of floating is displacement - this is how steel and iron ships float - they displace as much water than they weigh, and so are buoyant. –  Zhaph - Ben Duguid Dec 9 '11 at 9:05
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Yup. But I'm not sure the brick connections are water tight. I can imagine lots of designs using plates that will still let water into the "hull" I am more pointing out that you don't need to be all that water tight for the boat to actually float. Sebastian Wahl's answer nailed it tho! :-) –  albiglan Jan 19 '12 at 15:46
    
True - the fact that they aren't water tight was demonstrated very well by James May when he built his LEGO house, complete with wine glasses that leaked red wine everywhere ;) –  Zhaph - Ben Duguid Jan 19 '12 at 16:09

Yes, if built carefully. When I was a kid I made a number of lego boats to play with in the tub, and later in the pool. The main thing I remember was to make the hull upside down and out of at least two interlocking layers. Lining the inside with plate also helped.

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My children play with the lego fishing boat (see picture) in our bath tube. This design does have a serious flaw (imo). Even if there are very small water waves in our bath tube, water enters the boat which then becomes to heavy and sinks. So if you are planning to built your own lego boat i would make sure the sides are high enough to prevent water from entering the boat. Or if you are really clever make a water drainage system like normal boats have.

Lego fishing boat 4642

Lego fishing boat 4642

You also asked for some examples. Found this simple but effective example online.

Simple but effective design

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I'd have to say that in general, only the parts that are designed to float will do so reliably. You may be able to make some sort of raft by inverting several large bricks (studs down).

I haven't tried Lego bricks in water (other than a police boat set), however, when using Duplo's in the bath tub we were only able to make submerged structures. The water easily seeps into the bottoms of the bricks and causes them to sink.

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Yeah they float but make the hull wide not narrow as it will stay up right if you make the hull wide. Narrow means top heavy. I first started making LEGO boats now I make home built boats. And no need to be water tight for LEGO just get more surface area. Who knows you might even be able to make a cruise ship that floats.

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I was at the lake and I had a LEGO guy. I showed my mom, and it flung out of my hands. It went in the lake and floated.

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Yes, just as long as the bottom is able to displace the boats weight onto the water.. Just like how a Polar Bear can walk on thin ice; displacement.

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I think you don't mean 'thin ice' (Polar bears can't walk on thin ice, they fall through because they are heavy), but 'iceberg', where the buoyancy required to keep the iceberg afloat is provided by displacing an equivalent mass of water. Still: Wha?? That's the weirdest analogy ever. –  fredley Nov 2 '11 at 22:27
    
This answer's also not useful. "Do Lego bricks float?" "Yes, as long as they weigh less than an equivalent volume of water." That's nearly question-begging. –  user23 Nov 7 '11 at 11:09

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