Shadows! Shadows improve everything! Yours don`t seem realistic. I am sorry I can`t show you due to the time lack.
Define where the light source is. The shadow from the blue thing (thing without any dark spaces and with underlit ones, again) says it`s right above the boat, the shadow from the life lifebouy says it`s on the left (in relation to the boat). Add some shades to the forepart.
And one more thing relating to the composition: if you are planning that picture as a complete art (not in a context of something), add more details. Lots of them. Details are half way to a good art. Shades are the other one. Not the half, in fact, but they are very important.