I'm not quite sure what the question in the OP was. But if my guess is that when fueling overflows occur when the tank is only half full, my experience is that many folks assume that fueling up a boat is just like their car: insert fuel hose, put on automatic at full flow and wait til it clocks itself off.
Nothing is further from the truth. Fueling boats MUST be done carefully, because there is a difference between a boat and car (beyond the spelling

). Boats have vent lines, cars don't (at least as far as fueling is concerned). On many boats the vent line is a tad BELOW the top of the fuel inlet, meaning the fuel will overflow the vent first.
Whenever I refuel, I first determine how much fuel is required. I keep a very close track of my fuel use, and have determined over the course of the past 14 years that our engine uses around 1/2 gallon per hour of running time. 20 hours, 10 gallons, easy.
I hold the nozzle and never "lock" it. When I reach 7 or 8 gallons, I slow way, way down on the volume. Diesel fuel foams. When I hit 9 gallons, I stop for a minute or so, and add the last gallon very, very slowly.
I haven't had a vent leak in 13 years.
Just slow down and you shouldn't have any issues. That's, of course, if I understood your question correctly.
