[magic452]

Many captains did return home with a full load of fish and low fuel.

Shouldn't happen in the game. I assume you are out of Manila, so you should have plenty of fuel if you use it right.

Patrol on the surface at no more than 10 knots. Submerge only when necessary and only at low speed 3kn. or less for as little time as possible.
Full and flank speed and charging batteries eat fuel, use them only if necessary.

Magic