In a recent article here on OceanLines, we described a brand new development effort by a company called Marine Green to adapt smaller outboards for propane fuel. Since that article, I have been able to talk with the co-founder of Marine Green, none other than Bill Parlatore, the founder and current Founding Editor-at-Large of Passagemaker Magazine. Bill described the work he and co-founder Howard Brooks have done so far, as well as what has yet to be done to bring the new technology to market.
According to Parlatore, the genesis of the propane-powered outboard was his bad experience with phase separation in an E-10 gas outboard. After having replaced the Fuel Control Module two times he began thinking about a different fuel solution. Parlatore, not surprisingly, is a serious cruiser and his boat, Growler, has been featured on many pages of past Passagemaker issues. He knew that his outboard experiences were common in the cruising community, where the small outboards that typically power dinghies and tenders often go unused for long periods of time and are subject to the hazards of phase separation, not to mention the hassle of dealing with storing gasoline supplies for the motors. Parlatore says, “It’s the perfect example of necessity being the mother of invention.”
Parlatore sat down early last year with his neighbor, engineer Howard Brooks, and discussed creating a new fuel delivery system to power an outboard with propane. The key is the fuel delivery system, which replaces the carburetor or injectors and throttle body assembly on a gas-powered outboard. Since much of the complexity of a conventional carburetor deals with the transformation of the liquid fuel into a combustible gas, the propane fuel module is much simpler — propane comes out of the tank as a gas. That simplicity should translate into lower production costs down the road.
Although propane has a lower BTU content than gasoline per gallon, it has an equivalent octane rating of between 103 and 112, so the fuel economy difference is smaller than one might expect. Early testing suggests propane will deliver about five percent less performance over the entire RPM range compared to gasoline. Emissions, however, are expected to be substantially better and the company hopes to partner with a university engineering school to document the emissions performance and study manufacturing issues.
In tests over the summer, Parlatore discovered that the low-speed consumption was actually better for the propane, presumably because of the overly rich fuel-air mixtures common in gas engines at low RPM settings. Testing is focused right now on smaller engines that would be suitable for the dinghy/tender application, the center of which seems to be the 4-6 hp range. At 6 hp, says Parlatore, you’re looking at about a 55 pound engine, which most people can handle. On the small engines, the propane tank is attached to the engine frame and is easily re-filled with a connector from a standard propane tank. Larger engines have used typical 20 pound steel tanks, although Parlatore reports that a see-thru, 10-pound composite tank is not only much easier to handle, but is corrosion proof and allows you to judge remaining fuel levels accurately at a glance.
Summarizing his assessment of the propane potential, Parlatore notes that propane “doesn’t go bad; it doesn’t undergo phase change; it requires fewer oil changes for the motor, and gives you better economy and lower emissions.” Applications to smaller outboards look fairly straight forward, although at higher horsepower levels the propane will need to be delivered as a liquid which poses more complicated engineering issues. It’s clearly too soon to know how long before we will be able to buy propane-powered outboards, but you may be able to see them running at the upcoming Miami International Boat Show in mid-February. Stay tuned.
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