Instead of using white gouache or Chinese White, you'll need to plan a bit more beforehand to reserve the white areas and possibly use masking fluid for the mast, the boat and maybe the roof of the building and the waterlines around the banks. (arttutor.com)
Mixing watercolor and ink, without the use of masking fluid or tape, these surreal pieces are focused on utilizing the delicacy and unpredictability of the medium. (juxtapoz.com)
If you don't want to use masking fluid for the mast, ripples etc. you could use the point of a scalpel or razor blade to scratch out at the end, but only when the paper is bone - dry, otherwise it's likely to tear. (arttutor.com)