Not a boat but back when I was young and dumb I used to fly an old twin engine airplane with the screwiest fuel system I’ve ever dealt with. All return fuel went to the main (wingtip) tank on that side so burning from aux1 had to wait until some fuel had been used from the main. Aux2 fuel had to be pumped to the main for use. Things got complicated because the two engines returned different percentages of fuel, the aux tanks were different sizes, the aux2 transfer pumps ran at different rates, aux2 tanks had no fuel gauges and most of the rest of the gauges didn’t work. First time I flew it I landed with one tip tank full (probably over flowing) and the other almost empty. Took full control to keep the wings level. Finally figured out the tank sizes and flow rates to manage it but that was almost a full time job. I keep expecting to read about that plane in NTSB Reports.