Launched new for the 2017 model, Tohatsu’s 5 horsepower propane-powered outboard is sure to turn some heads dockside and appeal to those trying to make the world a better and cleaner place.

Propane or LPG (liquid petroleum gas) describes a family of flammable hydrocarbon gases that include propane, butane and mixtures of these two gasses. LPG is liquefied through pressurization and is a byproduct of the natural gas and oil refining process. LPG is very popular as a worldwide source of fuel and is currently being used to heat homes and trailers, cook food and run autos and fork lifts-and now four-stroke outboards. Propane is a form of LPG, but not all LPG is propane, so be advised.

Why would boaters consider a propane-powered outboard? Actually, there are a number of compelling reasons. First, you totally eliminate any possibility of ethanol-related fuel failures, like water, phase-separation, loss of octane, etc. An LPG-fueled engine typically requires less maintenance than traditional gasoline- powered outboards on critical fuel-related parts. These include hoses, gaskets, carburetor jets and valves, plus other critical links in the fuel chain. Propane is not as volatile as gasoline that’s sloshing around in a tank, whose liquid could potentially leak on your cockpit sole or down into your bilge area via a cracked tank or loose hose fitting. Propane engines typically start easier than their gasoline counterparts, with quieter operation and produce up to 30 percent cleaner exhaust emissions, all without compromising engine speed or power.

I reached out to Tohatsu’s engineering department to get a better understanding on how an LPG-powered outboard works. According to Tohatsu, “The MFS5C LPG is based on the MFS4/5/6C engine platform with some key changes to allow it to use LPG or propane. The MFS5C LPG comes from an existing reliable, proven and durable platform. The major component changes to the propane-powered version are the fuel regulator, the fuel shut off valve, the cylinder head, the mixer (replaces the carburetor) and the LPG fuel connector.

“During operation, the LPG enters the engine through the fuel connector and travels to the fuel regulator first. It takes the high pressure LPG coming from the LPG tank and steps it down in two stages from high pressure first to 6psi, and then from this midpressure down to 0.6psi.

“This process in the regulator brings the fuel pressure to a safe and usable pressure for the outboard. The fuel then travels to the fuel shut off valve. The shut off valve is controlled by a negative pressure supplied from the engine as the engine rotates. As soon as the engine ceases its rotation, the negative pressure stops and this immediately shuts the fuel flow off to the engine. The fuel shut off is normally in a closed position and is only opened with the engine rotating. This feature makes the MFS5C LPG safe, by only having low pressure LPG flow when the engine is operating. The fuel then flows from the fuel shut off valve to the mixer. The mixer does the same function as a carburetor, by mixing the fuel with air to send an atomized fuel/air charge into the combustion chamber. The updated cylinder head optimizes the combustion to offer a clean and reliable burn.” To ascertain how much fuel the propane- powered engine will burn compared to a gasoline version, Tohatsu’s engineers mentioned that the MFS5C LPG will run on a commercially available 11-pound propane tank for approximately five hours at wide open throttle. In contrast, the gasoline model’s fuel flow is 1-liter per hour (0.26 gph) at wide open throttle. The last time I filled up my BBQ tank it was $15. Assuming you are using $4 per gallon premium fuel at your local dockside filling station and the equivalent five-hour burn is about 1-1/2 gallons of 93-octane, the cost comparison is fairly easy. It will cost you $15 to run the propane powered 5-horsepower Tohatsu for five hours and $6 to run its gasoline fueled sister. What’s obvious from this A/B analysis is that most folks are not going to abandon their gasoline-fueled fourstrokes to run out and get propane outboards. However, for those of you that have propane onboard anyway (for either heat or cooking fuel), having a propane-powered outboard eliminates the need to carry potentially volatile gasoline, plus there are no worries about E10/E15 fuel related issues.

The MFS5C LPG is available in three different shaft lengths (S/15-inch; L/20-inch; XL/25-inch), so there is a size to fit your needs, whether it’s a portable outboard for your inflatable, dory or as an auxiliary/kicker. The choice is yours, but if you think that an LPG-powered outboard is in your future, the Tohatsu MFS5C LPG might be your ticket to ride.