Welcome to Subsim matey.
I assume you are playing SH3 1.4b (with no mods/supermods). If so, there are no refuelling boats in the game. There are however, friendly ports which might enable you to complete the patrol grid. Failing that, if you have the engine upgrades, you might be able to complete the patrol @ about 7-8kts. Ask your Nav Officer for 'Max distance at Current Speed' and then plot your route/+return to see if you can change speed and make it.
Or......pay no attention to your patrol grid and go somewhere else.
