Northwest Biodiesel Network

Marine Use of Biodiesel

Why use biodiesel in my boat?

Biodiesel use has environmental benefits, provides energy independence, supports local and rural communities, and provides superior engine performance; however, boaters primarily use biodiesel to eliminate the odor and toxic emissions from petroleum diesel. Petroleum diesel pollution is a serious health threat with more than 40 air toxins, while biodiesel significantly lowers emissions of sulfur dioxide, carbon monoxide and carcinogenic particulate matter.

Boaters often complain of the smoke from their diesel engines as well as the soot accumulation on the transoms and decks of their boats. Biodiesel noticeably and significantly reduces these issues. For maximum benefit, boaters choose B99 (99% biodiesel), however, at even a blend of B20, there is a noticeable reduction in smoke, soot, and noxious diesel odor from the engine's exhaust. Biodiesel boaters also report having no eye irritation from biodiesel exhaust.

Biodiesel has been used successfully by the U.S. Navy and National Park Service as well as private and commercial boaters the world over.

How is biodiesel better for the marine environment?

Studies by the National Institute for Occupational Safety and Health have shown that biodiesel will not harm fish. The California Department of Fish & Game has also documented the impact of biodiesel on native species of marsh plants and marine organisms and biodiesel was found to be much less toxic than petroleum fuels. Biodiesel degrades at the same rate as sugar, about four times faster than petroleum diesel. When blended with biodiesel, the degradation rate of petroleum diesel tripled when compared to diesel alone, according to a test by the University of Idaho.

Biodiesel also reduces water pollution because it burns more efficiently and results in less soot accumulation and particulate (smoke) emissions than petroleum diesel. Faster starting and smoother operation also reduce the discharge of unburned fuel into the water. Older boat engines in particular will emit less soot under load and less carbon black during startup.

How is biodiesel better for my marine engine?

Biodiesel provides superior lubricity and higher cetane than petroleum diesel. Sufficient fuel lubricity is necessary to reduce equipment wear and premature breakdown. Biodiesel’s higher lubricity enhances engine performance, prolongs engine life and decreases the engine’s operating costs. The higher cetane (similar to having a higher octane in gasoline) results in a more complete combustion of the fuel. The higher cetane also results in easier starting, smoother-running engine performance, and quieter, more reliable operation. Biodiesel improves engine efficiency, can improve the power output of the engine, and results in less white smoke.

If I start using biodiesel, can I go back to petroleum diesel?

With biodiesel, you can easily switch back and forth between biodiesel and petroleum diesel, and between various biodiesel blends.

Do I need to take any precautions when using biodiesel on my boat?

Fuel tanks in a marine environment are more likely to have water contamination from condensation. Water in petroleum diesel can lead to microbrial growth which can infect the fuel. Diesel-degrading microorganism growth appears to worsen in boats that are used infrequently since the inactivity allows the microbes to accumulate in stable colonies. These microbes that consume the fuel can create a layer of sediment at the bottom of the fuel tank. The action from the waves can cause the sediment on the bottom of the tank to mix with the rest of the fuel which can lead to clogged fuel filters. Biodiesel, with its biodegradable properties, can accelerate this microbrial growth in the fuel tank.

Due to its natural solvent qualities, blends of biodiesel higher than B20 can dissolve the accumulated petroleum deposits in fuel tanks when the fuel is first introduced. In order to prevent fuel filter clogging from both microbrial growth and accumulated sediment, clean the fuel system prior to using biodiesel. Then, be sure to monitor fuel filters and change them as needed and always keep a fuel filter on hand.

Biodiesel’s solvent qualities can also slowly degrade rubber fuel hoses, filter gaskets and seals when using blends of B50 or higher. Ultra low sulpher diesel also degrades rubber parts. Replace these parts with modern synthetic hoses and seals as needed. If a fuel line becomes soft, worn (or brittle from ultra low sulpher diesel) replace it with USCG-approved grade A-l fuel hose.

As an additional precaution to reduce moisture condensation, marine fuel tanks should be kept full, particularly in winter.

What about handling biodiesel?

Similar to any fuel, precautions should be taken when handling biodiesel. Although biodiesel is nontoxic, its solvent properties can result in the loosening of old paint on engines or on painted surfaces in the bilge. Besides staining raw wood surfaces, biodiesel has been shown to degrade polysulphide rubber compounds used on decks and is harmful to teak decks utilizing polysulfide seams (use extra caution when filling tanks via deck ports). Biodiesel can also harm rubber engine mounts if not cleaned up immediately. Use paper towels or absorbent pads to remove spilled biodiesel and then clean the surfaces thoroughly with warm soapy water.

What about using biodiesel for my onboard heater or stove?

Biodiesel has a higher flash point than petroleum diesel and is not flammable at room temperature. Boat heaters and stoves that rely on the ignition of fuel rather than the atomization of fuel will not work effectively with biodiesel. Boats that use the same fuel tank for both the main engine as well as a heater or stove, can use a blend of B20. Another option is to use petroleum diesel in the winter, when the heater is in use, and then transition to B99 in the summer. Boats that have a separate tank for the heater or stove should use petroleum diesel for their heating tanks but can use up to B99 for their main engine fuel.

Can I leave biodiesel in my tank over the winter months?

Many boaters do not use their vessels in the cold weather months which can be problematic for any type of fuel. To help prevent fuel storage concerns, keep fuel tanks full and use stability additives and commercial biocides as needed.

Do I need to worry about cold weather issues?

Biodiesel, like petroleum diesel, will gel at colder temperatures, normally starting around 32 degrees. However, this is usually not a concern for boaters because the water temperature is well above biodiesel’s gel point (for example, the average temperature in Puget Sound in the winter is 45 degrees). Most boat fuel tanks are located near the water side of the boat and are kept at a consistent temperature above the fuel’s gel point.

What about fuel quality?

All commercially sold biodiesel in the Northwest is required by law to meet quality standards created specifically for biodiesel known as ASTM (American Society for Testing and Materials) D 6751. These technical standards ensure consistent, high quality fuel that will perform properly in diesel engines.

Where can I find biodiesel for my boat?

Clicker here for a complete list of marinas that sell biodiesel. If your marina doesn’t sell biodiesel, make sure to ask them to carry it!

Our mission:

To promote the use and benefits of biodiesel through awareness campaigns, educational programs, and specific initiatives.

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