If all recreational boats had similar hulls and were used the same way by all boaters, optional power packages would be unnecessary. Of course, each yachtsman has his own agenda, pace and style, so the marketplace of diesel power is all about choices, lots of choices.

This year's new diesels are lighter, more compact and more economical than those of years past, with further advancement in electronic control module technology, which regulates an engine's behavior relative to system operations. Such innovation is great for new-yacht owners, as well as for those looking to repower. That's especially true in small and midrange boats, where the trend is toward gaining a few more knots, a little more range and better fuel efficiency.

Repowering an older boat is not always the right way to go. Upgrades don't automatically increase the resale value of your yacht. A previously owned boat is worth only what someone is willing to pay for her, when you are ready to sell. If you buy a 1986 model for $56,000 and add $60,000 worth of diesels, she'll still be worth no more than a pristine version of her old self, likely about $85,000, according to the "blue books of the marine industry.

For this reason-and because repowering often includes additional work on exhaust, propulsion and other systems-you should repower only if you plan to keep the boat for a minimum of five years to minimize your losses. Or, you should repower if expense is a secondary concern compared with increased horsepower, better economy, improved parts availability and enhanced reliability.

That's exactly what this year's crop of diesels offers. Here's a breakdown of new models from the industry's leading manufacturers.

CATERPILLAR

The new 700 hp Cat C-12 replaces the 3196 and, at 2,595 pounds, continues the trend of reducing weight and maintaining or increasing power. Improvements include upgraded electronic control, a new piston and ring package and improved breathing systems with changes to the turbo, exhaust manifold and aftercooler. Cat's trademarked ADEM III controller monitors and regulates engine vitals.

At its rated 2300 rpm, the engine's fuel consumption is 36 gallons per hour. The ideal vessel for this power package is likely 50 to 60 feet LOA.

Particulars: In-line 6-cylinder; 732 cid; 55.6" by 38.3" by 39.6"; 2,595 pounds. Caterpillar engines are available from 300 to 3,000 hp. Caterpillar Inc., (800) 321-7332; www.cat-marine.com.

CUMMINS MERCRUISER

Mercury and Cummins Marine have created a new entity based on a joint venture. Though distribution will remain status quo for now, look for a combined effort in the near future.

Cummins Marine's latest offering is a boosted-horsepower version of the QSM 11. The unit is rated at 660 hp at 2300 rpm. For extended engine life and lower rebuild costs, the design utilizes replaceable wet cylinder liners. Turbocharged and aftercooled, this six-cylinder uses Cummins' Quantum System, which optimizes performance and relays data quickly and accurately. The QSM 11 has an optional digital data display that centralizes all engine information. A syncro, backup throttle and slow idle are all within the electronics package.

Particulars: In-line 6-cylinder; 661 cid; 53.3" by 38.65" by 39.85"; 2,475 pounds. Cummins engines are available from 120 to 660 hp. Cummins MerCrusier Diesel Marine, (800) DIESELS; www.cummins.com.

MerCruiser's new entry is the D4.2L EHO, a direct-injected 300 hp engine with turbocharger and aftercooler that will match up with Bravo outdrives. Horsepower is rated at 3600 to 3800 rpm.

Particulars for the D4.2L EHO: In-line 6-cylinder; 254 cid; 4.2 liters; 50" by 30" by 21"; 1,296 pounds. MerCruiser engines are available from 120 hp to 300 hp. Mercury Marine, (800) MERCURY; www.mercurymarine.com.

LUGGER

Lugger, associated closely with commercial applications worldwide, is now gaining momentum within recreational boating ranks.

The company's newest model, and already one of its most popular, is the L6140AL2, a high-output unit that develops 700 hp at 2100 rpm. This in-line design affords a high horsepower-to-weight ratio, one Lugger touts as economical to run.

The engine is turbocharged and aftercooled, and the aftercooler uses fresh water rather than a more corrosion-prone seawater system. The guts are a Komatsu industrial-duty block, and the engine has individual heads and nodular iron pistons.

Particulars: In-line 6-cylinder; 930 cid; 73.53" by 40.18" by 46.5"; 3,317 pounds. Luggers are available from 70 to 900 hp. Alaska Diesel Electric, (206) 789-3880; www.northern-lights.com.

MAN

MAN has a new 1,500 hp engine, along with a recently unveiled 450 hp package that is working its way into the pipeline.

The big boy is the 12-cylinder, 21.93-liter D 2842 LE 409 rated at 2300 rpm. Systems monitoring is handled by an electronic diesel control that integrates into its electronic instrumentation. As with most monitoring systems, alarms blast if oil pressure or temperature fluctuates too much, and diagnosis for any engine irregularities can be made from a laptop. The engine has a two-step turbocharger and electronic injection.

The D 0836 LE 401 is an in-line six-cylinder rated at 2600 rpm that weighs 1,474 pounds and is controlled by the same MAN monitoring system.

Particulars for the D 2842 LE 409: V-12, 21.931 liters; 81.51" by 53.12" by 57.88"; 4,488 pounds. MAN engines are available from 450 hp to 1,500 hp. MAN Engines & Components Inc.; (800) MAN-2842, www.man-mec.com.

SCANIA

Scania enjoys an excellent reputation in its truck and bus endeavors, and the new 800 hp DI16M is the company's largest venture in marine applications, with indications that the horsepower rating will increase. This 16-liter, light-duty engine is rated at 2100 rpm and based on a V-8 truck block. The DI16M replaces the DI14M and delivers two liters more displacement in a stubbier, shorter package than its predecessor. It has twin turbos and intercoolers, direct fuel injection, and redesigned pistons and heat exchangers.

Scania also has developed its own electronic unit injectors and engine management control module.

Particulars: V-8; 978 cid; 48.75" by 45.94" by 44.85"; 3,410 pounds. Scania engines are available from 43 to 800 hp. Scania USA Inc., (210) 403-0007; fax (210) 403-0211; contact@scaniausainc.com; www.scania.com.

VOLVO PENTA

During the past year, Volvo Penta rolled out its KAD 300/DP and KAMD 300, nearly identical engines that offer either a Duoprop sterndrive or a straight inboard option.

The 285 hp, six-cylinder, electronically controlled engines have four-valve technology, replaceable wet cylinder liners and valve seats. Fuel is regulated by an EDC unit and dispersed by a two-stage injector system. Both units are high-revving and rated at 3800 rpm.

Many new midrange luxury cruiser designs take advantage of sterndrive power, which, of course, allows the engines to be mounted aft, freeing up living space.

Particulars for the KAMD 300: In-line 6-cylinder; 219 cid; 54.7" by 31" by 28.9"; 1,188 pounds. Volvo Penta engines are available from 100 to 700 hp. Volvo Penta, (757) 436-2800; fax (757) 436-5150; www.volvopenta.com.