Aside from what's been mentioned the shading on the under water details looks a bit wonky as well. Other than that it's one hell of a first drawing!
How exactly, is it the bilge keel?
The bilge keel is one of the issues. Given how it's angled it should be lighter on the side we can see, not darker.
The propeller and shaft should be shaded light-base-dark, rather than dark-base-dark and now that Novice mentions it, the transition from shaft to hull could do with some remodelling.
Also, I've realised that the shading on the superstructure is a bit confused. You've got the funnel shaped as if the light is coming from the front, ie it's lighter on the front edge, whereas the superstructure is shaded as if it's coming from the rear. Which way you choose to shade it is up to you, there's AFAIK no official direction, so long as it's consistent.
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