Seafarers' fatigue

Any stories to tell about the above?

I was talking to an old salt the other day about fatigue and he explained that he used to sit in a small boat offshore for 48 hours on watch on 4.5 hours sleep. As an eight-hours at least sleep person, I can't imagine caring whether ships bumped into each other or not after a while. In my usual state, I'd care very much. Poor sleep means poor decisions. How do you keep fresh on watch? Answers please to Lizzie Gates.

And very many thanks.