When this new regulation was first proposed, boaters, boatbuilders, and boat dealers balked. It was estimated that upgrading from a non-converter carbureted stern drive engine to an electronically fuel injected one with converters would cost a builder around $6,000. There were also safety concerns: Nothing this hot belongs on a boat—particularly a gasoline-powered one. (U.S. Coast Guard regulations state that the exterior of any engine component cannot exceed 200F.)
So engineers had to come up with a new kind of catalytic converter with components that could withstand the harsh marine environment and run at a proper temperature yet not pose a safety hazard. In 2006 Indmar Products Company did just that with its Extreme Tuned Exhaust with Catalyst (ETX/CAT), the first production catalytic converter for gasoline-powered inboard marine engines. The key to its EPA award-winning design is a ceramic substrate that reportedly will not rust or corrode. Other engine builders like MerCruiser are using less expensive all-metal substrates, asserting that they can withstand contact with water. Which is better? Only time will tell.
Indmar also developed a new converter enclosure, a seamless, one-piece design that is said to eliminate the chance of water reaching the oxygen sensor and catalyst. To keep the converter's exterior at a safe temperature, Indmar created a raw-water-cooled jacket that reportedly allows the system to meet the USCG's 200F regulation.
Inside the converter, stainless steel mesh holds the catalysts in place, according to Indmar, even during rough conditions. The interior has also been designed to be easily serviceable; remove an O-shape snap ring and you can replace the interior components.
So the safety and durability issues have been addressed. What about other concerns? One is that a converter will reduce engine output. Well, good news boaters, preliminary tests not only show no measurable loss in power, they actually point to an increase in fuel economy because the electronic fuel injection and oxygen sensor more efficiently control fuel delivery.
Which leaves the issue of cost. Nobody ever said new technology came cheap but things may not be as bad as originally predicted. MerCruiser expects its catalytic converter-equipped engines between 130 and 400 hp to cost on average 15 percent more, not including freight, tax, installation, or accessories. Note this is the MSRP for engines sold through a dealer and not necessarily representative of the price as a part of a new-boat purchase. In other words, this would be what you would pay were you to walk into a MerCruiser dealer and ask to buy a complete stern-drive package. Builders routinely mark up the cost of all components that go into a boat, engines included.
So basically it's a done deal: Come 2010, gasoline-powered marine engines will have catalytic converters, which the EPA estimates will take 600 million tons of hydrocarbons, 130 million tons of nitrogen oxide, and 1.5 million tons of carbon monoxide out of the atmosphere annually. Is it all worth it? Our lungs may think so, but we'll have to check back with our wallets.
This article originally appeared in the January 2009 issue of Power & Motoryacht magazine.