Take a long look at a big Mercury
By John Fleming
Diesel engines may be a very good investment for the owner with a larger houseboat, especially if he/she intends to keep the vessel for a long period of time. Houseboat manufacturers have largely stuck to gasoline-powered engines using inboard, outboard and stern drive units in the past.
Gasoline-powered engines provide high horsepower ratings with low weight. They offer good speed, and the initial cost is comparatively low. For these reasons they are very popular with houseboat manufacturers and owners alike.
The diesel engine is generally heavier than a gasoline-powered engine, for a given amount of horsepower, and the initial cost is greater. These are negative aspects, yet there are other considerations and some of those favor the diesel engine.
Consider the safety factor. One tablespoon of atomized gasoline has the explosive potential of three pounds of dynamite! How many tablespoons full of gasoline are to be found in a 100-gallon tank? Moreover, the gasoline fuel ignites much more easily than diesel and it costs a good deal more.
Considering the fact that the diesel-powered engine generally burns less of that cheaper fuel for each horsepower that it develops, ordinarily lasts longer than a gasoline-powered engine and is much safer, we may need to take another look at diesel power for the houseboat.
It may be easy to order a new houseboat with diesel power, but suppose that I already have a houseboat, the engines are old or whacked out, and I am considering a repower. How hard is it to change over to a diesel-powered engine? If you are presently using an outboard engine for propulsion, the cost may be prohibitive.
If you are using a stern drive engine/s or an inboard engine, the changeover could be quite simple. In fact, with the right diesel engine it can be a snap.
Mercury Marine is one of a number of manufacturers that builds light, high-speed diesels for both inboard and stern drive applications. For stern drive installations, the conversion to diesel may be an easy bolt-in. Many of these engines will bolt directly up to your present Mercruiser, Bravo stern drive without modification.
The inboard engine may represent an easy change over as well. The bell housing on the inboard versions of the Mercury Diesel engines has a standard bolt pattern that makes them adaptable to many different brands and types of inboard transmissions. Thus the conversion from your present gasoline engine to a Mercury diesel may be easier than you think.
In many instances, the transmission that came from the factory on the big block, gasoline-powered engine presently in your boat will also fit the Mercury diesel. There are a few other considerations. The diesel engine requires two fuel lines rather than one. The second fuel line returns unburned fuel from the injectors to the fuel tank.
Understandably, this line is referred to as a “return line.” Some engine installers will return this line to a fitting on the fuel filter to save running the extra line all the way back to the tank and making the needed modifications to the tank which are necessary to accept it.
DO NOT ACCEPT THIS PRACTICE ON YOUR CONVERSION! The fuel is heated as it passes through the injectors. It can cool off as it passes to and through the fuel tank again but if it is returned to the filter for a period of time, the fuel becomes quite warm. At this point you begin to pass heated fuel back to the engine