The fuel you burn while boating is a significant part of your annual boating cost. Every boater is aware of this and tries to follow some of the guidelines that promote fuel savings.
In keeping with the Boat Blurb tips policy, I will try in this article to list most of the factors that contribute to higher fuel costs and how you can avoid them. Take a read through these factors to see some of the actions you can take to save fuel and thereby reduce your overall cost of boating.
While there are enormous differences between boats and motors, there are many common fuel saving factors that apply to most powerboats. Let's focus on these tips and then provide some interesting dollar saving stats about outboard motors.
Everyone seems to know that as engine horsepower increases, so does the amount of fuel it takes to operate the motor. But with any given engine size, not everyone seems to understand how much fuel burn increases as you run your engine speed into the higher end of its RPM levels. By far, the best way to increase your boat’s fuel economy is to run your engine at conservative RPM levels and not at wide open throttle. For example, if you run a 150 hp outboard at wide open throttle on a standard runabout, you will burn just over 14 gallons per hour. But if you run that same outboard at just under 4,000 RPM, you will burn less than half of the fuel that you use while running wide open. In other words, if you are concerned with fuel economy, get into the habit of running your outboard motor in the 3,800 RPM range. The speed difference will not be a major factor on your trip time, but the savings will be large. Think about running 65 to 80 percent of maximum power the next time you go boating and be pleasantly surprised at the money you save.
Find a happy medium for your throttle. Most boaters don’t choose to travel around at idle speeds, but if they do, they are using too much fuel. At idle speeds and very slow speeds, you will use less fuel but you will not get very far. At idle speed, a boat is a displacement hull and only after it is running fast enough to be on plane is it running efficiently. So in order to not waste fuel, once you are out of slow speed zones, throttle your boat up onto plane for better economy.
Weather can also be a significant cause of excess fuel consumption and one that is easy to forget about. Rough water and waves require constant throttle and trim adjustments and these consistent changes burn excess fuel. Fair weather boaters don’t have to worry about this.
All boats, as with airplanes, have weight limitations. Recommended weights are carefully calculated and frequently posted by the manufacturer at the helm seat. The hull on almost any boat will deliver lower fuel economy and even a dangerous ride if pushed to take on unnecessary weight. Plan on what you take in your boat, just as if you were trying to avoid extra baggage charges on an airline flight.
When calculating added weight in your boat, don’t forget about the fuel. A lot of boaters prefer to have full gas tanks every time they leave the dock, but this is not really necessary for short trips. Of course, you must always have sufficient fuel onboard, so just consider the “Rule of Thirds." This refers to having 1/3 of the quantity you have in your tank being sufficient to get you to your destination, 1/3 to get you back home, and a final 1/3 in reserve for any emergencies or delays. Any additional fuel weight will result in a higher fuel burn.
Another way to spend excessive money on fuel is to have a boat with unnecessary drag. My Keep Your Bottom Clean rule is what matters here. Even a thin film on your boat bottom will add drag that translates to poor mileage. Using a long handle brush, scrub away any marine growth or debris to bring your boat bottom back to smooth and clean.
Here is a fuel saver tip that is actually hard to believe. A tiny nick or burred leading edge on your propeller is a problem. I have performed prop tests where we added bumps to the prop’s flat blade surface and even drilled holes in them. The results were minimal. But when the leading edge of the prop had even a slight roughness, both fuel economy and performance tanked. Inspect your prop closely. If there is a slight roughness on the leading edge, you may be able to carefully file it smooth. Otherwise spend the money on a new stainless prop. It’s worth it.
Ever wonder if buying a completely different propeller could improve fuel economy? Different blade area, number of blades, pitch, diameter, rake, cupping, barrel length or blade shape, can all produce different results. If you put a significant number of hours on your boat each year, consult with a propeller specialist to ensure that you are using the best possible propeller.
Once you have taken all of the above fuel saving actions, consider how you might improve your own driving technique. Make good and constant use of your boat trim. Use the seat of your pants and a visual check of how close to the stern the spray from your boat is exiting from your boat hull, and make minor adjustments accordingly to your trim. The seat of your pants can detect any small ride improvements you make and the position of your boat spray will tell you how much of your boat is experiencing water drag. Trimming your boat properly is very much an ongoing activity and can greatly improve fuel burn.
Tabs (if you have them) are also important to achieve an economical as well as comfortable ride. While tabs can change the longitudinal ride of your boat, they are best known for keeping you boat riding level, from side to side. If your boat is running along as if the circus fat lady was planted on one side, bring it back to an upright ride using your tabs. Boat hulls are not designed to operate with one side of the deep V running flat on the water.
Give some thought to where you ask your passengers to sit. The objective being to distribute weight evenly. This also helps your boat to run approximately three degrees bow up from its at-rest waterline, and also not leaning to one side or the other. I call such seat selection ‘manual trimming’.
While air flow may not be as important as water flow, air flow is still a factor. Ask any sailor. A seasoned power boater knows how tricky it is to dock a boat with high free board on a breezy day. For this reason, a good powerboat design undergoes wind tests as well as water tests and these have resulted in some surprising findings. A canvas or Bimini top is great for sun protection, but you will pay for it with lower fuel economy. Even subtle additions such as giant speakers mounted on a cockpit arch create added air drag. Be considerate of air drag the next time you go out in your boat.
Here’s one you didn’t think of: always use the oil that is recommended by the motor manufacturer. Substituting a different oil type can cause increased parts friction and lead to higher fuel consumption.
Finally, shorter trips mean less engine operation, so a little route planning before you head out will result in less money spent on fuel. Do you take the shortest route around that island, or do you go the long way around out of habit? The longer the trip, the more important the planning.
There are many interesting statistics readily available regarding powerboat fuel consumption. Here are some to consider: a gas outboard motor, running at wide open throttle will consume a number each hour that is about 10% of its rated horsepower. Therefore, a 150 horsepower outboard at a full 6,000 RPM will consume about 15 gallons (56.75 L) of gas per hour. Using Mercury Marine’s own test numbers, their 150 hp Verado 4-stroke burns 14.2 gallons per hour on a medium sized runabout and achieves 30 to 33 miles per hour. The formula holds true for different horsepower. Our small 5 hp outboard burned a half gallon per hour, also 10% of its horsepower. At the high end of horsepower, we see some “savings." According to Mercury tests, their 600 hp V12 only burns 51.0 gallons/hour. Of course the word “only” may not apply to someone trying to save money on fuel. Especially if there are several V12s on the transom.
Simply put, the first two numbers of your outboard’s horsepower rating can tell you approximately what amount of fuel your outboard will burn per hour at WOT. As a side note, I would add that available tests seem to confirm that while 2-stroke engines can be faster, 4-stroke engines are usually more fuel-efficient.
I will conclude by presenting an example of dollar savings you can achieve by running at slightly lower RPM levels. From Mercury tests we know that a 250 hp Verado 4-stroke outboard burned 26.1 gph. Running the same motor at around 75% of its rated power (or 4,500 RPM), their numbers showed a fuel consumption of 12.5 gph. This is an amazing savings of over 50%. If we paid $5 a gallon for gas and ran a two hour boat trip, the dollar saving would be $136.00.
The conclusion is clear. If you operate your outboard RPM level between 70% and 80% of maximum, you will save big on fuel costs, plus the added benefit of having a little more time to enjoy the view.
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