Racer- Wire a test light to coil positive and drive it. See if you lose power there when it dies. What year/make/sbc? Friend of a friend also has a ski boat same problem, turned out to be ect sensor failing and telling module it was overheated> module shuts motor down. Assuming you have EFI.
About how far are we planning to drive the boats, don't want to buy fuel at marina as I'm bringing my own on truck. Should I bring gas cans on boat?