Interesting game.
If I'd change something I'd make player and sub hitboxes smaller and increase or even completely remove the time limit.
The two player mechanic seems quite original, but (at least with my keyboard) you can't control both submarine and player at the same time which makes things more difficult.
The music is a plus. I am not a fan of the art-style, but it's a plus that you drew it by yourself.
Good job!