Boat Fuel and Ethanol: E10, E15 and Safe Refueling

Boat Fuel and Ethanol: E10, E15 and Safe Refueling

Fueling a boat looks like filling a car, but there are two big differences. First, fuel vapor on a boat can collect in the hull and explode. Second, some fuel sold at gas stations is illegal to use in a boat engine. This guide covers which fuels are allowed, what happens if you misfuel, how to fuel safely at the dock, what to do about a spill, and how to handle ethanol fuel in winter storage. Sources are the US Environmental Protection Agency (EPA) and Discover Boating, the consumer program of the National Marine Manufacturers Association (NMMA).

Which fuel is legal

Why misfueling is a growing risk

Discover Boating explains that the federal Renewable Fuel Standard requires increasing amounts of biofuel in the fuel supply. That puts more E15 on the market, often at the expense of ethanol-free fuel. Discover Boating estimates that about 95% of boats are filled at ordinary gas stations, where E15 may sit right next to E10. It also cites a Harris Poll finding that:

What misfueling does

Discover Boating lists stalling, corrosion, fuel leaks, damaged valves and complete engine failure. It also cites a Department of Energy study that found E15 caused hotter operating temperatures, unintended clutch engagement, erratic running and engine-part failure. Discover Boating adds that insurance usually won't cover misfueling damage, because negligence is involved. Check your own policy.

If you misfuel

Don't run the engine. Discover Boating describes the fix: pump the bad fuel out with a suction pump (a motorized one for larger boats) into a sealed container, disconnect the fuel lines, clean the tank with fuel-tank cleaner, rinse it, pump out the rinse water, then reconnect the lines and refill with the correct fuel. If you're unsure, call a marine technician, and dispose of the contaminated fuel properly.

How to refuel safely

Discover Boating says gasoline vapor is heavier than air, so on a boat it can settle low in the hull and create a fire risk. Diesel fumes are less risky. Gas boats with enclosed engine compartments need the most care.

Before you pump

  1. Tie the boat securely to the fuel dock.
  2. Shut off the engine, put out any open flames, and turn off electronics, including the ignition, to avoid sparks.
  3. No smoking.
  4. Close ports, hatches and doors so vapor can't drift inside.
  5. Get passengers off the boat while you fuel.

While fueling

After fueling

  1. Open ports, hatches and doors to air the boat out.
  2. Check the bilge for leaks.
  3. If your boat has a bilge blower, run it for at least four minutes before starting the engine. Discover Boating says to run it after every fill-up, and any time you start an inboard after a break. Outboards without enclosed engine compartments don't need this step.
  4. Do a sniff test. If you smell gas, don't start the engine. Find the leak first.
  5. Start the engine, then bring passengers back aboard.

Spills must be reported

Discover Boating notes that any fuel spill that leaves a sheen on the water must by law be reported to the US Coast Guard through the National Response Center: 800-424-8802.

Ethanol fuel and storage

Ethanol absorbs water. In a guest article on Discover Boating, the BoatUS and AMA presidents explain that ethanol-blended fuel stored for a long time can phase-separate, leaving a corrosive layer of water and ethanol at the bottom of the tank. They report that half of BoatUS survey respondents had repaired or replaced engine or fuel-system parts because of suspected ethanol damage, at an average cost of about $1,000.

Their advice for winter:

Discover Boating also warns against using fuel more than about 30 days old, storing gasoline in unsafe containers, and putting equipment away for a long time without dealing with the leftover fuel. See our winterizing guide.

Budgeting for fuel

Fuel is often one of the largest running costs. Enter your engine's typical burn rate and local fuel price in the True Cost tool to see the yearly total.

Sources