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Posted by on Mar 15, 2011 in Runabouts, UK, US |

Marine Diesel Ready for Runabouts

Cummins MerCruiser and Volkswagen Marine team up to produce a series of 4-, 6-, and 8-cylinder diesels.

A few years ago at a Donzi dealer meeting, the company was showcasing one of its 22 Classics powered by a Yanmar inline six-cylinder diesel and pushed along with a little Arneson surface drive. I couldn’t wait to drive it. I thought it would be great with the diesel powertrain.

VW’s TDI 265-6 three-liter V6 diesel will be mated to MerCruiser’s Bravo 1 and Bravo 3 sterndrives.

VW’s TDI 265-6 three-liter V6 diesel will be mated to MerCruiser’s Bravo 1 and Bravo 3 sterndrives.

And it was. Top speed was greater than the 60-mph benchmark for performance boats, fuel consumption was as miserly as you can get in a 22-foot runabout, and smoke was minimal — and that was before low-sulphur diesel was mandated.

But it still wasn’t ready for prime time. Back then, there wasn’t a sterndrive that could handle the torque of the diesel, even the small six-cylinder in the Donzi. Yanmar didn’t make a sterndrive then—though it does now—so the Arneson was about the only thing available to spin a prop. As robust as these drives are, they’re not for everyone.

For starters, the Arneson is a surface-piercing drive, which requires a deft hand to operate. What’s more, it extends far beyond the transom, which can create problems: Surfacing propellers are sharp, and you don’t want your kids to get cut while they’re supposed to be having fun swimming. The props are expensive, and because the Arneson drive is so long, they’re in harm’s way while towing. And docking isn’t as easy as it is with a sterndrive. Like I said, that powertrain in a Donzi 22 Classic was a great idea, but it had its limitations.

Now, I think the industry has advanced to the point where small diesel powertrains are not only possible in a runabout package, but maybe even preferable.

At the 2011 Miami International Boat Show, Cummins MerCruiser debuted a new line of diesel engines produced in a strategic partnership with Volkswagen Marine: an inline four-cylinder, a 4.2-liter V8, and a 3.0-liter V6.

The V6 caught my attention because it’s the same engine used in the Volkswagen Touareg TDI. Having driven a 2010 Touareg TDI for a weeklong test, I fell in love with the 3.0-liter diesel. It’s a real gem. Foremost, it is efficient. The 5,300-pound SUV netted 25 mpg on the highway, and 20 mpg while towing a 4,300-pound trailer. What’s more, it’s torquey, quiet, and clean, already meeting EPA Tier 2 emissions standards. Here’s the best part: It now can be mated to MerCruiser Bravo One and Bravo Three drives, or used in inboard applications with a ZF transmission. That means all those limitations present on that Donzi 22 Classic are a thing of the past.

Available in 225-, 230- and 265-hp output levels, all three TDI V6 engines achieve maximum torque at 2,000 rpm. That means you can twirl a higher-pitch propeller, and that translates to higher speeds at lower rpm. Fewer rpm means lower fuel consumption, something every boater can appreciate. The TDI V6 also is compact. It will fit under the same engine cover as a regular small-block Chevrolet or 90-degree V6 engine.

From my perspective, there’s no downside to installing the TDI V6 in any manufacturer’s runabout. Whether the consumer bites? Likely that will come down to pricing. Unfortunately, Cummins MerCruiser doesn’t release retail prices for its products, in part because it’s largely boat manufacturers that buy them, not general consumers. Now might be the right time for diesel to make a splash in the runabout and tow-boat markets, as long as the powertrains aren’t overpriced.

But consider this: The retail price for a 5.0-liter V8 with a Bravo One drive starts at $19,700, and with catalyst exhaust, closed cooling, and other options it can total as much as $24,400, according to Steve Fleming, communications director for Mercury Marine. It’s difficult to imagine the TDI 3.0 liter costing that much more. If it’s just a few thousand dollars, it would be worth it, particularly if you plan to finance the purchase. Who wouldn’t pay $50 or so more a month to have an efficient diesel under the “doghouse?”

I’m curious what real-world boaters think. Would you pay a little extra up front on the sticker price for diesel power to save on fuel costs every season?
—Brett Becker