[xvector]

You can read about the logistics from countless sources.

For most boats, it's not a straight shot to the US, they often refuel from boats at sea or utilize refueling points in Central America; or perform a handoff in Puerto Rico or the Dominican Republic.

They don't "need the fuel to get back," the boats are scuttled on arrival. The value of the boats and fuel is a rounding error compared to the value of the drugs.