Fuel Economy and Your Boat
In the summer of 2006 American consumers entered a second year of rapidly increasing fuel prices and boaters especially felt the pinch. With prices typically topping well over $3.00 per gallon for gasoline what can boaters do to stretch their fuel dollar? The two options are to maximize the fuel economy of your boat—or tie your boat up and hope for some relief. Our bet is that high fuel prices are here to stay, so your best option if you want to stay on the water is to look at your boat’s engine and fuel system, and your own boating habits to lighten the load on your wallet.
What can you do? Here are some ideas gleaned from personal experience, talks with boat mechanics and a search through available literature. These will focus on gasoline-powered boats, but some of the concepts apply just as well to diesels. Sail boaters typically don’t have to worry about this subject, but as sailboats increasingly come with more auxiliary horsepower, some of this can apply to them as well.
Let’s start with an easy solution that gets directly at the price of fuel. Generally automotive fuel station gasoline prices are lower than those offered by marinas. If you trailer your boat find the best price at an automotive station and top your tanks up there. It may not be as easy as filling up at dockside due to the height of your boat’s deck off the ground, but if it’s manageable you’ll save money. Pay close attention to the fuel shutoff so you don’t pump money on to the pavement.
If you rely on marina fuel points for your regular fill-ups you will be stuck with higher prices. If that’s your situation then it’s time to look at ways to use as little fuel as possible and still enjoy all that your boat has to offer. Start with your boat’s engine and fuel systems to minimize your gallons per hour.
The Engine
Whether an outboard or inboard gasoline engine, a simple way to keep your engine running efficiently is to monitor your spark plugs and change them regularly. This is especially true of older engines with carburetion and traditional ignition systems. Newer engines use electronic systems and fuel injection that create a more efficient burn in the cylinders, reducing the tendency for plug problems and the need for tune-ups. Pull your spark plugs every so often and inspect for fouling, tip wear or burning. Make sure they are the ones recommended for the engine and properly gapped. If the plugs do show signs of problems it’s time to tune the engine, which should include a leak-down and compression test as the engine ages and parts such as rings begin to wear out. If your engine is in top condition and running correctly then it will use fuel as efficiently as it can.
Making sure your fuel system is clean and the fuel fresh is also important. Clogged fuel filters will decrease your engine’s performance and increase fuel consumption. A good rule of thumb is to change your fuel filter every 100 hours or annually depending on how much time you put on your boat. If you do not use your boat very often, consider adding a stabilizing additive to keep the fuel from degrading. Finally, make sure you are using fuel approved for your engine. Each manufacturer has a slightly different standard for what fuels they approve for their engines, and issues bulletins about alcohol additives that are a particular concern because they can potentially cause degradation of fuel system components leading to poor performance or possibly failure.
If your engine is running properly then knowing if it is running most efficiently can be determined by your speed through the water measured against fuel flow. This is not easy to measure with an outboard motor, but the manufacturers usually publish a graph of fuel use against speed on a typical hull style. By studying the graph and making your own notes you will get a sense of when the boat is moving with the best speed on the least amount of power. And it isn’t rocket surgery to understand that if you can stand to run down the bay without the “throttle in the corner” you will notice a significant reduction in fuel use.
The same is true of inboard powered boats, except that many newer boats will have a fuel flow meter that can simplify throttle settings versus speed. If you don’t have a fuel flow meter they are relatively easy to install and can pay for themselves in savings.
Fuel efficiency also depends on a proper match between the engine and the hull, and this also includes the propeller. The engine has to have enough power to move the hull without being overworked, which increases fuel use. Similarly, too powerful an engine for the hull merely wastes fuel—there is a right horsepower match for every hull. The propeller transmits all that horsepower to the water, so a correctly sized propeller will drive the hull with the most efficiency. If your engine is working too hard due to an undersized or oversized prop then you are wasting fuel. At full throttle the engine’s RPM should match the manufacturers recommended specifications. If you’ve bought a used boat double-check that the propeller, especially on an outboard, is the correct one.
The advent of the four-stroke outboard motor has enabled great increases in fuel economy. If your budget allows it, consider swapping an older two-stroke motor for a four-stroke. Although heavier, the fuel savings will be evident immediately, as will the clean running nature of these motors. Again, match the motor and propeller to your hull.
The Hull
A clean hull is important to maximizing its efficiency in moving through the water. If you trailer your boat it’s easy to keep the bottom clean and smooth. However, if you keep your boat in the water during boating season, marine growth in the form of barnacles, mussels and various forms of algae will accumulate on your boat bottom and around areas like the propeller shaft, rudder, zincs, through-hulls and swim ladder. This is true of fresh or saltwater. The only way to see what’s going on down there and clean it is to go for a swim or haul the boat—or beach it if you’re the old-fashioned type. Give it a good scrubbing and apply a quality anti-fouling paint recommended for your hull material and conditions. While you are at it, assess whether your hull is structurally smooth to minimize drag. A smooth hull is a happy hull, and easier on your wallet.
Efficient operation
The engine is tuned, propeller sized correctly and the boat hull clean and smooth. Now what can you do?
Well, it all comes down to your boating style under power and your real needs once underway. Certainly there are great fuel savings to be had by running at slower speeds, but be sure that the speed you pick is also most efficient for the hull. Planing hulls need to get up on their “step”, but once there can be throttled back and still run in the “sweet spot”. Easing the throttle up instead of slamming it forward is an obvious way to avoid excessive fuel use, especially on carbureted engines. Even displacement hulls have a sweet spot—find it and enjoy the savings in fuel and engine wear and tear.
You can also reduce your fuel use by doing a little trip planning. Unless you are an un-reformed “gunk-holer”, taking the straightest line to your destination makes sense. Less time enroute means less fuel used. Take advantage of current and tide to give you faster speed over the ground for the same engine speed. Avoiding travel on foul, windy days with rough seas will also make a difference. Use your fuel flow gages and navigation electronics to their best advantage in planning and executing your trip. Here are some other tips to cut down on your fuel use:
• Keep dodgers and other canvas appendages down unless really needed. Those units can add a load of wind resistance and drag.
• Dinghy’s and inflatables cause considerable drag when towed behind. If you can bring these boats on deck or into davits make the effort to do so.
• Don’t load your boat with things you don’t really need. Lighten up the weight and you’ll decrease the demand on your engine.
• Load your boat evenly—this is especially true of small boats that are more susceptible to weight distribution.
So, if you get that queasy feeling in your stomach when you have to fill your fuel tanks, we hope you don’t decide to just tie your boat up in the backyard. Remember that there are things you can do to ease the fuel-cost pain and continue boating. Pay attention to your boat’s engine and hull—and your boat driving habits—and you’ll see some relief.