Iceships

[Pye-rate]

Tis is a little farther than most people want to take this idea.
http://www.springer.com/us/book/9783319226767

[JoeStrout]

This is really interesting. I haven't read the book, but at first blush, my concern would be mass. Water is heavy, and if you build your entire ship out of it, it's going to be a lot of mass to push around. Heavy is fine for space colonies, but not so much for ships.

My second concern, of course, would be my spaceship melting (or sublimating) around me. In the outer solar system it'd be fine, but in the inner solar system, I would think your ship would essentially become a comet, with a long tail of stuff that used to be your ship extending outward from the Sun.

[Pye-rate]

Comet tail cool! An easy way to track automated cargoes coming in from the outer system.