Where there's low smoke there's fire. 

DIESEL EXHAUST fumes are a lot like houseguests and fish: it doesn't take long before they really stink. It's the fear of fumes men choose gasoline engines over the oil screws. Big-boat owners, however, don't have that choice. But they don't necessarily have to face the sooty fog, either.

In fact, after testing a pair of four-cycle MAN D2842 LE V-12 diesels, I'd say the German engine builder has snuffed the smoke without giving up any power.

This is the latest version of MAN's long-proven V-12, and it's currently rated at 1,020 hp, up from the 959 hp of the D2842 LYs we tested on a Viking 65 Motor Yacht more than two years ago.

This time, our test platform was a new Hatteras 54 Convertible provided by Capt. Bob Hoste of Cape Island Yacht Sales in Pt. Pleasant, New Jersey. The MANs pushed the Hatteras to a top speed of 35.2 mph, and proved to be a blend of smart technology and practical engineering.

White smoke is common on diesels at start-up because the engine is cold and combustion is incomplete. That's great if you want to wipe out generations of mosquitos in a Jersey swamp, but most of us don't like to leave our dockmates tasting diesel when we pull out in the morning.

The D28 series of twin turbocharged and aftercooled diesels has a cylinder cut-out mechanism that's part of the Bosch fuel-injection system. At low speeds (start-up and idle), one bank of cylinders doesn't fire because fuel is not supplied to that side. This lowers emissions from the get-go and cuts sound levels. As engine load and rpm increase (around 1000 turns), the second bank kicks in. It's totally automatic and quite undetectable.

With only half the cylinders firing, docking is smooth and there's no jumping around as is common with many high-horsepower engines. But when I goosed the throttles, the 70,000-pound Hatteras was on plane in 10 seconds. You could've gotten more smoke out of a Marlboro Light.

But limiting fuel isn't the only way MAN cuts low-speed smoke. To keep the burn clean, the turbochargers are set up to pump high volumes of air at low rpm. This approach also helps explain the brisk acceleration. To prevent over-boost as speed increases, there are, of course, waste gates on each turbo.

A block heater also is part of the smoke-stifling package. Warming the iron helps the cylinders and pistons fit just right, which means less blowby and lower oil consumption.

Overall, this is a mechanical approach to cutting smoke. By contrast, Detroit Diesel attacks the problem electronically on its popular 1,075-hp DDC 12V-92TA DDEC. Detroit limits smoke by employing a computer that controls injection timing.

MAN goes its own way in other areas, too. While we're used to seeing big diesels draped with hoses and tubing, MAN uses internal cast-aluminum and steel lines to plumb coolant and lubricant. This saves weight and space. With transmission, the MAN weighs 4,267 pounds, 658 less than the 12V-92TA. And with its 3'4" height (the 12V-92TA is 4'3" tall), the D2842 LE 402 left ample over-the-top working space aboard our Hatteras convertible.

Cylinder heads are individual and weigh about 10 pounds apiece. A good mechanic can remove and inspect a piston in 30 minutes. On our test boat, I had no problem getting around the engines. The low profile let me easily reach the twin spin-on secondary fuel filters and simultaneously work the adjacent hand-operated priming pump. Hatteras also supplies electric priming pumps. These are important items because MAN insists you install dry fuel filters and fill them with the pump. Why? Because if you fill a new filter from an open container, you could unknowingly add contaminants, such as water and dirt, woefully close to the injection pump.

The biggest inconvenience I see with the MANs is removing the inverted dual-canister type oil filters. Have a bucket, plastic bag and rags ready.

You know that black cloud that's supposed to follow you offshore and back with diesels? Well, it looks like clever engineering is blowing it away.

This review/article originally appeared in Boating Magazine, November 1994 and is written by Peter Frederiksen. For more great powerboat reviews, visit their website and subscribe at: http://subscriptions.boatingmag.com/