How Much Fuel Capacity Do I Really Need?

Why boat captains should think more like airline pilots

- Alan Jones

One of the worst feelings in boating is the rising tension that occurs when you realize you've miscalculated fuel consumption and your boat might not make it to your destination. The absolute worst feeling is when the engine begins to sputter and then goes silent. When buying a boat, one of the most important considerations is whether or not it will have the range to safely transport you to the places you want to go and back home again. Unlike cars, boats are subject to more variables, so just looking at boat-test results and factoring in the size of a gas tank won't be enough information to make the right call. Being conservative and thinking like an airline pilot instead of a bus driver should be the mindset.

PROBLEM 1: NOT ALL THE FUEL IN THE TANK IS USABLE

You should only fill a tank to 90 to 95 percent of its capacity to allow for expansion when it gets hot and prevent gas from escaping from the vent when fuel sloshes in the tank. Nonspill vents are supposed to prevent this, but it can still happen if a tank is overfilled.

You'll also lose some gallons because your fuel pickup doesn't extend to the bottom of your tank. This prevents it from vacuuming up the nasty bits of crud that can accumulate over time, along with water from condensation that is heavier than gasoline. A safe bet is to shave 5 to 10 percent off your boat's published capacity by assuming it can't be used. Right from the get-go, and perhaps to your dismay, that generous 200-gallon tank might only provide 160 gallons of usable fuel.