IN THE OLD DAYS WHEN YOU RAN A DIESEL-POWERED BOAT, THE DRILL WAS SIMPLE. FIRE IT UP, MAKE SURE WATER WAS COMING OUT THE EXHAUST AND PULL AWAY FROM THE DOCK.

Once underway, you'd shove the throttle to the corner, see how much muscle the iron was giving you that day and then pull it back a couple hundred off the top. That's where the throttle stayed until you slowed down to fish or shut down for the night. I made 33 trips from New England to Florida this way and never did as much as bust a rocker arm.

And when it came to powering a boat in the 40-something-foot range, the answer was usually just as simple. It came from Detroit, and was a pair of six-cylinder engines of either the 71 or 92 series.

But those days are over. Especially now that Caterpillar and Germany's MAN, tired of sniffing DDC's smoke, have fired new volleys in the six-cylinder-diesel wars. Cat has the 582-hp 3176B. MAN, the 574-hp 2866 LE401. And when you put these new engines up against Detroit's latest incarnation of the venerable 6V-92 - the 605-hp 6V-92TIA DDEC III - the decision becomes difficult indeed.

Of course some might say, "Wait a minute, the answer's easy! The Cat is a brand-new powerplant designed from the ground up as an electronically controlled engine. We all know that electronics improve everything." 

Others might counter, "Hold on, it's an established track record that's most important. And since the 6V-92 has been around for decades, glitches are a long-lost memory. Plus, it has the latest version of Detroit's sea-proven DDEC electronic control system."

Then, the old-time hard-liners will maintain that electronics are just so much silicone and wire, and what really counts is cubic-inch displacement. And in that regard, the MAN is the hands-down winner. At 731 cubic inches, the MAN has 102 more inches than the Cat and 179 more than the Detroit.

So who's right?

SHOWDOWN ON THE RIVER. To find out, I gathered three virtually identical Ocean Yachts 48 Super Sports. The only difference were one carried Cats, the other Detroits, and the third MANs. Almost $2 million worth of sportfishing prowess, turning a combined 36 cylinders and pumping a total of 3,600 hp.

I ran them on South Jersey's Mullica River last spring and autumn, and here are the results:

SPEED. The Caterpillar and Detroit boats topped out at 38.6 mph. The MAN hit 38 mph.

FUEL CONSUMPTION. It didn't vary much except at WOT at which the Cat boat burned 12.2 gph less than the MANs and 19 gph less than the Detroits. The reasons? One may be true efficiency. Another is that above 2320 the fuel gets cut back on the Cat to reduce prop overrun. Our test engines were turning 40 rpm over their factory spec of 2300. A bit more prop pitch may have been needed. 

SMOKING. The Cat and the Detroit seemed almost gas-engine clean. And the MANs gave off nothing more offensive than a light white mist.

PRICE. The 48 Super Sport lists for $592,000 for either the Cat or Detroit, and $601,000 with the MANs.

In these categories, the engines are all about the same. But in others they're quite different. For instance:

SIZE. MAN's 2866 LE 401, with 731-cid, packs the most swept volume in its six cylinders. Yet it's the most compact of the three: 5" narrower than the Cat and 7" slimmer than the Detroit. It's also 3" shorter than the Cat, which is 1" taller than the Detroit. The MANs are clearly the best fit.

In-line six-cylinder diesels clearly take up less space than a V-6, but the German engine still packs more cid than its American counterparts.

The reason for this is that like the Cat, the MAN is an in-line engine. This saves room. Also, most of the MAN's components and fluid passages are molded into the block. At the other extreme, the Detroit has its cylinders arranged in a V, and many of its components are attached externally in the form of hoses, pumps and tubing. Obviously, a bulkier setup.

ACCELERATION. The MAN was the fastest from idle to WOT, besting the Cat by five seconds and the Detroit by eight. Credit this performance to the earlier boost pressure of the MAN's waste gate that allows the turbocharger to provide abundant air for combustion at lower engine speeds. The MAN also has the largest bore, 5.04" and the longest stroke, 6.10". These dimensions let the MAN develop torque quickly, which is important since the engine is rated at 2200 rpm compared to 2300 for the others.

ENGINEERING. Each powerplant represents a different approach to design and systems. And these are perhaps the most important differences of all.

RATING GAME. The Caterpillar and MAN are four-strokes; the Detroit is a two-cycle. A four-stroke operates on the familiar principle of intake, compression, power, exhaust. During these strokes, ports and valves open specifically for breathing and evacuating the cylinders. In a two-stroke, however, the pistons fire twice as often and the engine is working harder. This explains how the 6V-92 develops 605 hp out of the smallest displacement (552 cid).

From an emissions standpoint, the two-stroke is dirtier, since the engine breathes and scavenges air at the same time. As air comes in, exhaust is pushed out. That's why there's that mist in the engine room and oil vapor in the exhaust. That's also why you're always adding oil to a two-stroke diesel.

Although on paper, all three engines produce roughly the same horsepower, and they offered similar top speeds in our tests, on any given day their performance could change dramatically. One explanation is how the engine-builders come up with their horsepower figures.

Caterpillar and Detroit both rate their engines' output based on an air temperature of 77 degrees. Most engine rooms, including the Ocean 48's run hotter than that. This means incoming air is less dense. As it gets warmer, the horsepower output may fade. 

MAN is more conservative and claims there will be no reduction in power until the air temperature exceeds 113 degrees. This may not mean that much on a brisk spring day when the air and water are cool, or when the boat is new and hasn't reached its midstride fighting weight. But in New Jersey during August when the air is so thick with humidity you need a Furuno just to clear the dock, or down off of Walker's Cay in May when the surface water temperature is 78 degrees, there's no doubt the MAN is going to be less affected.

CONTROLLING INTEREST. Another big difference, of course, is in what controls this horsepower. The Cat and Detroit both use an electronic control module (ECM) to feed information to the engine. The MAN is strictly mechanical. 

Like the auto companies before them, America's diesel-builders see federal emissions regulations just a short way down the road, and not much farther down the waterway.

So to control smoke, electronic systems have been devised for truck engines as well as marine powerplants. As our Cat and Detroit test engines proved, there are other benefits to packing electronic brains into the iron, but the fundamental reason lies in emissions.

The Cat's ECM is a seagoing computer with internal power supplies, sensor inputs, a central processing unit, actuator outputs and two serial data links. You hardly need to be a computer wiz to understand what the ECM can do. Just consider how your brain controls your body.

For example, stick your head outside the door on a freezing morning and your brain tells you to wear a coat. 

The same morning when you fire up the 3176B, its brain senses the temperature in its cooling system and regulates the fuel flow to the electronic unit injectors. A cold engine won't burn all the fuel injected until it warms up. In the meantime, the excess fuel turns to white smoke. It's great for killing mosquitos but rough on the guy in the next slip and your crew in the cockpit. With the ECM regulating the fuel-injection timing, emissions are reduced and cold starts are easy without the need for block heaters, chemical starting aids or low-viscosity lubricants.

The ECM also operates an electronic governor. This lets you adjust the low-speed idle down to 550 rpm, or up to 750 rpm -handy when coming into the dock or trolling. If you also want trolling valves, the option can be added easily and the governor will limit engine speed to prevent damage to the valves if you advance the throttles too much.

Nine sensors monitor data such as fuel temperature, inlet manifold pressure and coolant temperature, and two speed or timing sensors act as a backup should one fail.

Synchronizing is standard, and a data link connects to an engine-monitor system (EMS). Each engine has a bank of three monitors which display temperatures, fuel flow, boost and percent of load.

I like the analog gauges. Even though symbols are used to display engine oil pressure and gear temperature, at least you can see a needle move into the red. At any time, just punch a pad on the parameter bank and you get a digital readout.

But I found these LCD readouts sometimes hard to see, especially when wearing Polarized sunglasses. And not just on the Cat boat. The Detroit DDEC has the same problem if the monitor is mounted on a flat or angled. 

Perhaps the nicest thing about the Cat system is that only two wires from the ECM to the EMS are required to transmit all engine/gear data. Makes for a tidy engine installation and eliminates a host of connections.

MOTOWN MOTION. My first Detroit Diesel 6V-92 had 435 hp. Today's engine is rated at 605 hp. Although this isn't a new powerplant, with its DDEC electronic control system, it is state-of-the-art iron.

DDEC has been used on truck engines since 1985, and appeared on boats in 1987. This is the third generation of the system. Like the Cat, it has electronic fuel injectors. There are no mechanical adjustments or linkages. The governor is controlled by electronics. Low idle, synchronizer, an ECM, and an electronic display module are standard, and a diagnostic reader is used to troubleshoot. There's a backup microprocessor should the main one fail, and that should get you home. And like the Cat, it requires 10 volts to keep it running. The Cat can get by, however, on 8 volts.

The engine has a series of self-checks and continuously monitors internal functions; these results can be called up for review with the proper diagnostic software. 

During cold starts it doesn't smoke because DDEC advances the timing and the engine runs on half of its cylinders. This allows the engine to warm up rapidly, and with less fuel being burned, there are lower emissions. When you put the engine under load - such as going into gear - all cylinders begin to fire.

The ability of the engine to sense a loading condition proved itself in our test. At speed, when I turned the helm hard over, the engines didn't falter. Ordinarily, in this situation, both engines will drop rpm slightly, the inboard one due to pressure from the turn and the outboard engine because it's laboring from the drag of the other. With DDEC, the governor senses the change in load and supplies more fuel to maintain the set rpm.

Unlike the three-bank monitor on each Cat, the Detroit has one DDEC display module for each engine. It always displays engine rpm, coolant temperature, oil pressure, fuel consumption rate, battery voltage, gear oil temperature, and gear oil pressure. I prefer this bank over the Cat's because in addition to symbols, each function is named. The only time you press a pad is to scroll the menu of options. The main menu alone has 46 choices ranging from engine hours to the amount of fuel consumed.

If you're not a tech head, this can be information overload. Then again, it's said people only use about ten percent of their total brain capacity. The point is, electronically controlled engines can tell you more about what's going on inside your engine than regular gauges on a mechanical engine. But does it really matter? It depends what you want and whether or not you'll use it.

THE MAN IS HERE. Unlike the Cat and Detroit, MAN's 2844 doesn't use electronics to combat emissions. From the start it was designed to be a clean-running engine. One way it does this is with its by-pass cooling system. 

When the engine is cold, for example, no raw water enters the intercooler. This results in warmer temperatures for combustion because the engine heats up very quickly. And there's a long-term benefit here as well that the electronic engines can't match.

When the air is cold, condensation can form in the combustion chambers, and the vapor goes on the cylinder walls until it's burned off. But over time, winter storage, for instance, this build-up of condensation can pit the cylinder walls. Since the MAN heats up so rapidly and the cooling system doesn't kick in until the engine is warm, basically the interior and exterior of the 2844 always run at the proper temperature. The MAN will smoke slightly on a cold start-up, but clears in a couple of minutes. 

BOTTOM LINE. As our test proved, an electronically controlled engine is not necessarily the best choice. The wizardry may help prolong your engine's longevity if you use all the data to spot problems before they become crises. But on the other hand, MAN seems to have a great deal of faith in their thoroughly uncomputerized iron, guaranteeing the rated horsepower for up to 2,000 hours per year, with 300 of those hours at WOT. The Detroit is rated for 500 hours per year, with 50 hours at WOT. Cat calculates engine life at 6,000 to 8,000 hours before overhaul based on 100,000 gallon fuel consumption, since wear is directly related to piston travel, more than any other factor.

Keep in mind that electronics can't correct bad fuel, a dinged prop or a dirty bottom. They'll only let you know the condition is worsening. But so will mechanical gauges, like you'll find on the MAN boat.

So which one would I pick if I were specing out a brand-new Ocean Yachts 48? I've had very good experiences with both Detroits and Cats on my boats, and I'd be very tempted by the quietness, speed and fuel-efficiency of these new Caterpillars. I also would feel the pull of the Detroits' strong track-record. But in this case, I'd go with the MANs. I like the clean-looking package, and their compactness makes them easy to work on aboard this Ocean. I'm also a believer in maximizing cubic-inch displacement, and I like MAN's real-world approach to power ratings. The downside? The MANs cost more, and MAN mechanics aren't on as many docks as Cat and Detroit wrenches. Then again, not every mechanic of American iron can deal with electronics. 

But c'mon, nothing is as simple as it used to be. 

This review/article originally appeared in Boating Magazine, April 1996 and is written by Peter Frederiksen. For more great powerboat reviews, visit their website and subscribe at: http://subscriptions.boatingmag.com/