Fascinating stuff. The boats have a cartoony element about that that really appeals to me. The article is a bit light on construction details but if you head over the modellers blog (In Japanese but this is the Google translate version) there is more information.
Close up, the models show all the crudeness of modestly priced 3D printing but on the water, you can live with this. There is some clever work with home-printed impellers and miniature outboard motors.
The boats are made up of several components, each printed in the required colour. In this respect the method follows traditional injection moulding, but of course 3D print allows people to try things out without thousands of pounds of tooling costs.
If you want to know more, it's well worth digging through the blog and there is a "warts'n'all" approach with bad prints being shown. I have a feeling that this would be ideal for home based printing kit. If only I had the time/space/money....