Choose colours lemon yellow, raw sienna, prussian blue, neutral tint (or paynes grey which has a little more blue)

the neutral tint will give a very strong dark colour

founex port1   atmo tree2   atmo tree final   founex port final
Roughly sketch the composition. You can use masking fluid for the masts or you can paint them in with white gouache at the end. Paint clean water on the top of the composition above the boats. Paint on raw sienna in the middle section above the horizon line while the paper is still wet. It will look very dark but will dry 30% lighter. Drop in more sienna + blue while the paper is wet, BUT once it starts to dry results can be unpredicatable.   Dry completely - paper should be flat. Use the same colours to build up darker tones on the background trees. Keep the sky quite light. Paint prussian and lemon in the midground add a little prussian in the water in the middle painting carefully around the boats.Dry   Paint foreground with clean water and drop in blue and blue + sienna leave the buoys white.   Add more darks to foreground make sure your strokes are horizontal. Add more masts using white gouache.