Change of plans, from catamaran to box keel

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My initial plan of a catamaran hull has advantages, like being super stable and having lots of storage space down low. Parts of the hulls can also be sealed into flotation chambers to keep the vessel afloat in case of an emergency.

There are definitely also some disadvantages, the biggest being the lack of interior space. The tunnel in the middle means standing-height in the middle isn’t really an option.

So I’ve been thinking about changing the design to a box keel hull. I would sacrifice some stability for a more practical interior. The keel would have to be wide enough to provide some walking space, but small enough to not push the boat up and make it want to tip over. For now I’ve made it about 70 cm wide and 20 cm deep. This gives is about 400 kg upward pressure, which should match the weight of the empty vessel.

Time for another prototype…

1:10 scale box keel
Weighed down with the equivalent of 400 kg, the designed dry weight of the boat
An additional 180 kg to scale, simulating 2 people and some equipment. It all looks good so far…
The same 400 kg dry weight + 180 kg cargo all at one side

As the last picture shows, the box keel is not as stable as a catamaran. By far. I will not be able to carry  the 10 or 12 people the catamaran could. But all in all it does seem to hold up, even in pretty extreme situations. Good results. I think box keel is here to stay.

Until next time…

Flotation test prototype

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I like the catamaran-like hull shape because it gives huge amounts of stability for a relatively small displacement. To actually test the stability I’ve made a 1:10 scale prototype from styrofoam and hot-glue.

I did some test by adding the weight of a couple of people (to scale). The model kept beautifully stable. 2 people sitting on one side of the boat will not be a problem. She even managed to carry the weight of about 10-12 people without too much trouble.

It all starts with a plan…

This is the excerpt for your very first post.

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I’ve been walking around with this idea for a tiny house boat for a while. Every now and then the idea pops up and turns into a small doodle on a Sunday morning.


A few specs:

  • It should sleep at least 2 comfortably.
  • It should be stable and sturdy.
  • It should preferably have electric (silent) propulsion.
  • It should be small enough to pass under most bridges here in the Netherlands, which limits the height to 2.5 meters, preferably less.