Boat Carbon Footprint

Information Center

Annual Boat Fuel Consumption

Calculating your Boat Carbon Footprint requires knowing how much fuel your boat consumes in a year. This page helps you determine your annual fuel consumption.

This page is part of the Boat Carbon Footprint Information Center and is a Polson Enterprises web site.

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Estimating Annual Fuel Consumption of My Boat

As mentioned on our main page, there are at least three ways to estimate your annual fuel consumption.

  • Write the number of gallons purchased on your fuel purchase receipts and and add them up at the end of the year.
  • Keep good records for one typical boating outing and multiply the gallons consumed by the typical number of boating outing you make a year.
  • Identify your boat motor and use average fuel consumption estimates for it (or twice it if you run twins)
Don't forget to include kicker motors, generators or other fossil fuel engines on your boat.

This page will help you with the third approach.

Duty Cycle

To test engines in closer to "real life" situations, engineers use duty cycles that approximate real use. For example, they may run slow a while, cruise a while, fast a while, cruise a while, slow a while and then repeat. The International Council of Marine Industry Associations (ICOMIA) has established a duty cycle testing marine engines. The duty cycle used by the EPA is sometimes called the E4 duty cycle.

Data from these tests can be used to estimate fuel consumption in the "real life" environment. However, most of the emission data collected focus Hydrocarbons(HC) (chemical compounds containing both hydrogen and carbon), and Nitros Oxides (NOX) emissions, not on Carbon Dioxide. But, if you know the amount of fuel consumed you can calculate the amount of Carbon Dioxide.

Fuel Consumption Data Supplied by Engine Manufacturers

Some marine drive manufacturers supply average fuel consumption information in terms of gallons per hour at a specific RPM. These are usually provided at fairly high throttle positions and may not be reprsentative of all your boating operations. But may still be of help in estimating your Boat Carbon Footprint.

Some Previous Estimates of Annual Fuel Consumption by Recreational Boats

A 1998 study on allocating motor fuel taxes in Ohio estimated the 1995 fuel use per watercraft at 299.7 gallons.

Estimating Your Fuel Consumption From Engine Horsepower

Calculating Fuel Consumption by Brett Becker published in the December 1998 issue of Boating Life provides some formulas for estimating fuel consumption based on engine horsepower.

Fuel efficiency is measured in pounds of fuel used be horsepower hour (officially called "brake-specific fuel consumption"). The article reports an in tune four stroke gas engines burn about .4 to .4 pounds of fuel for hour for each unit of horsepower, similarly, an intune two stroke outboard burns about .6 to .8 pounds of fuel per horsepower. Note, these numbers apply at peak horsepower, which is typically near full throttle. Fuel consumption is less at cruising speeds. Also, newer engines with loop-charged intake systems, fuel injection and direct injection have better fuel efficiency than older cross-flow fuel systems that were manufactured as late as 1990.

These estimates apply to carbureted and fuel-injected engines, but not to direct-injected engines like Mercury's OptiMax and OMC's FICHT models.

For two stroke engines you can just divide the horsepower by 10 to get fuel consumption in gallons per hour (.6 pounds of fuel / HP hr) * HP * (1 gallon / 6 pounds of fuel) = .1 * HP gallons/hr

Estimating Fuel Consumption by Annual Number of Outings

You can estimate the amount of fuel you typically burn on one outing and multiply that by the average number of outings per year.

2002 National Recreational Boating Survey published by Strategic Research Group 30 November 2003 estimated the mean number of boating days (half of the boats boat more days and half boat fewer days) for specific types of boats. Their estimates included two numbers, one from mean boating days by the primary operator, the second is for mean boating days by a seconday operator (like your son, neighbor or fishing buddy you loaned your boat to). Your average number of boating days may be more or less depending on your location (length of boating season) and your personal situation. But this data may be useful as a guide when you estimater your number of boating days.

Mean Number of Boating Days

Boat Type
Primary Operator
Secondary Operator
Total
Inflatable 11.78 1.84 13.62
Pontoon Boat 19.22 3.43 22.65
Houseboat 17.15 1.11 18.26
Open Motorboat 29.48 3.21 32.69
Cabin Motorboat 31.58 2.68 34.26
Personal Watercraft 14.26 3.93 18.19

Calculating Your Boat Carbon Footprint From Fuel Consumption

Carbon Dioxide production is directly proportional to fuel consumption. One gallon of gasoline = 19.4 pounds of CO2 and one gallon of diesel = 22.2 pounds of CO2.

Reference Average Carbon Dioxide Emissions Resulting from Gasoline and Diesel Fuel. EPA Emission Facts. EPA420F-05-001. February 2005.

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