Dreaming of ships, deep seas, waves, killing people.

The head represents the thought. On the boat, you explained that you wanted to achieve a goal. In this process, you have a psychological conflict. The struggle you see in your dream is a metaphor for this conflict. One of your ideas and thoughts wants to "kill" another idea and suppress it to the subconscious (sea). Finally, he hung him up, which means you made a compromise in it. That's what you have to do. The subconscious is unfathomable. You can't let the extreme thoughts of the moment be completely controlled.