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No Time to be Fuelish

When it comes to the fuel for your boat’s engines, it’s not as simple as the gas in your car
All those ponies can burn a lot of fuel, so make sure you keep one-third of your fuel supply in reserve in case of an emergency or a change of plans.

All those ponies can burn a lot of fuel, so make sure you keep one-third of your fuel supply in reserve in case of an emergency or a change of plans.

Today’s higher gas and diesel prices might tempt a captain to depart with less fuel, but the one-third rule should always be adhered to for safety. This rule simply states you should use one-third of the boat’s fuel to go out, another third for the ride home, and a final third for reserve in case weather or sea conditions extend your trip beyond your original plan. Pushing a towrope back to the dock—or God forbid, floating around on the open ocean—is not the way you want to end your day.

While most vessels are equipped with a fuel gauge to remind you how much go-go juice is in your tank, inaccurate readings are not uncommon. So, it’s wise to familiarize yourself with your read-out to make sure it’s reporting accurately at all times. If the fuel tank sender is located near the rear of the tank and the boat is on plane with the bow riding high, the gauge may lead you to believe your tank is full. But if you slow down and the fuel levels out in the tank, you could suddenly find yourself with significantly less than what first appeared on the gauge. Fuel gauges also have been known to fail, especially if they are old or when there is an issue with the float that’s supposed to rise and descend as the fuel level changes. Corrosion on any of the electrical connections can also pose connectivity issues.

Even when a fuel gauge is accurate it can fool you, especially if you are aboard a new or unfamiliar boat. I once delivered a new 42-footer with triple outboards for a friend who told me his boat had ample gas and was also outfitted with a reserve. Studying the fuel gauge, I noted F and R marks and a few hash lines on the face. I pulled into the dock with the needle smack on the R and filled up the 500-gallon tank with 490 gallons. Unbeknownst to my friend, the R on his gauge meant refill and not reserve. Although he now knew approximately how much fuel he could pull from the tank, I explained it was important to avoid running the tank that low. This was a new boat with a new tank, but water or other impurities would eventually gather at the bottom of the tank, which he’d not want to reach his motors.

A good way to reveal if the fuel sender is doing its job accurately is to keep a written log of how much fuel you take on at every fill-up. When you compare those numbers to the engine hours and boating activities you will begin to collect a history of how much fuel you are using on a typical trip. Nowadays, most engine gauges include a boat’s fuel burn, miles per gallon and how much range is left in the tank, but if the boat experiences some kind of electrical mishap, this information can disappear.

The popularity of large boats with triple and quad outboards means more time at the fuel dock topping off the tanks. This is not a job that can be rushed so make sure you have enough dock lines at the bow, stern and spring line cleats and be generous with fenders to protect the hull as traffic moves past the dock. Gasoline fumes are explosive, and no short cuts should ever be taken when fueling. Spill just one one cup of gasoline in the bilge and its fumes and an errant spark from an electrical accessory can ruin your weekend, if not your life. Gasoline fumes are heavier than air and seek out the lowest portions of the bilge. Although I have never seen someone accidentally inserting a fuel nozzle into a flush rod holder and pumping gasoline into the bilge, I believe only the skipper, or an assigned member of the crew, should be handling the pumping. This person should remain at the fill site until the tank is full. Leaving an active hose unattended is an accident waiting to happen. Larger outboard-powered boats may also carry a diesel generator with a dedicated fill and the twain should never meet. Always be sure when the dock-master hands you the pump nozzle that it is the correct one. I have seen this error made on a busy fuel dock, and it’s not a pretty sight.

Even though, big outboard-powered boats may lack the interior spaces of an inboard gasoline-powered cruiser, it is still advisable to shut down air conditioning systems and close cabin doors and hatches to prevent fumes from collecting before pumping gasoline. When the fueling is complete and the fill caps are back in place, open the doors and activate any blowers or fans you may have to remove fumes. Inboard powered boats will have a fume detector, but they are not always common on the larger outboard boats, so use the best sniffer of all, your nose. If you smell gas fumes wait until the air clears before starting the engine.

Although it is not necessary to keep your outboard tanks full, it is never a good idea to run them close to empty, which can allow condensation to form on the inner tank walls. Although the fuel filter and water separator should provide clean gas to the engines, there is no need to tempt fate with your fuel supply and engine health.

Last, but not least, manage your fuel burn. If you have multiple outboards, maybe alternate between engines when trolling to halve the running hours. Or to maximize range, find that sweet spot that delivers a comfortable ride and save those wide-open-throttle thrills for calm water, when you can enjoy all the horses pushing your boat. 

This article was originally published in the September 2022 issue.

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