Ink with watercolor exercise

This exercise should actually have been a little, wooden boat. According to Michael Warr's book "Capturing texture", that is. But I've drawn a boat two weeks ago, so I choose a subject which is a little closer to me than boats.
The exercise is about how you can put texture into an inked drawing by adding watercolor. In this exercise it also had to be a monochromic study. I like black and white drawings most, so that's what I've made. I think it has depth and a certain "breadness", although it's in black and white.