I made a quick fix to the boat... I put a wall on the upper part, where you would see a wall.
You should probably go back and shade that, or make a wall yourself for it, because otherwise it lacks a lot of the depth it needs.
I'd also suggest trying a different color instead of the default brown from msPaint (or default brown in whatever paint program you're using) A brown that would suit a wooden boat would work.
Maybe also have at least 3 shades... like a dark shade, normal shade, and light shade... adding little details to the boat will also help make it look better overall.