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September 21, 2007

Re-Power Play

Thinking about new engines? Diesels are better than ever.
DROP-IN UPGRADE: Sticking with the old boat? New diesels can boost performance and pay for themselves.
Photo: Courtesy of Volvo Penta

Curt Kiser has a plan. When he found a 1978 Bertram 28 to restore after a lengthy search, he knew he'd have a long list of upgrades and improvements to make. But a top priority is replacing the boat's 16-year-old inboard gas engines. He's already decided on new power—a pair of turbocharged four-cylinder diesels.

"I've owned a diesel-powered boat before and really liked it," said Kiser, a Tallahassee, Florida, attorney. "Diesels require less maintenance than gas, and they last longer. But the safety factor is paramount. My wife and I plan on taking the boat down to the Keys and Tortugas on extended trips to fish, and I really like the range and safety of diesels versus gas."

Kiser's decision represents a trend among owners of older, mid-sized fishing boats. With gas prices approaching record levels again this summer, combined with technological advances in weight reduction and fuel efficiency, electronically controlled diesel engines are a viable option for anglers replacing older gas inboard or sterndrive engines.

Diesel Pros
Today's diesel engines have significant advantages over gas. For starters, diesel fuel offers less chance of fire in engine spaces than gasoline, which is an important consideration when you're miles offshore. Diesels typically last two to three times as long as comparable gas engines. They also produce more torque, which equals a shorter time to plane and improved handling under heavier loads. Diesel engines are also designed to operate closer to their maximum rev limit, which means more top-end speed when you need it.

As a rule, less is more with diesels. According to Stig Timm, product manager for Volvo Penta marine diesels, a 25-foot sportfishing boat could handle a pair of 225- to 265-horsepower engines. A 40-footer boosts that capacity to twin 500s.

Because of improved power-to-weight ratios, smaller-horsepower diesels can equal or exceed the performance of the gas engines. For example, a Bertram 35 Convertible with twin blown, 340-horsepower MerCruiser gas engines was recently refit with a pair of 310-horsepower Volvo Penta D6 diesels. Now the boat cruises at 24 miles per hour while burning 21 gallons of fuel per hour. It tops out at 32 miles per hour with a 36-gallon-per-hour fuel burn—similar performance with better efficiency.

An even swap of power and weight can boost speed and acceleration more significantly, but there are tradeoffs. Diesels are roughly twice as expensive as gas engines, although up-front costs will be offset by fuel economy and range over a long life span. "You're going to burn one-third to one-half less fuel with diesels than you would with gas cruising the same distance," says Kevin Carlan, sales manager for Mastry Engine Center in St. Petersburg, Florida. The company averages 20 Yanmar diesel re-power jobs per month and those numbers are rising with gas prices.

"Diesel costs anywhere from 30 to 70 cents less per gallon," Carlan said. "So if you're going to keep your boat and put hours on it, the upgrade will definitely make a savings difference."

Inboard Insights
Fuel savings aside, there are other factors to consider before making the diesel switch. The new engine should fit into the existing space without sacrificing room for service. Heavier blocks might require reinforced engine beds or other structural modifications. A steady inflow of fresh air and the proper venting of exhaust will keep the engines running at maximum efficiency. Instruments for the new engines probably won't fit the existing holes in the helm dashboard.

The fuel system may require an upgrade to make it diesel-compatible. Galvanized tanks must be replaced since diesel has an unwanted chemical reaction with them, but stainless steel, aluminum or fiberglass tanks are fine. Diesels need a return fuel line from each engine to the tank, and the boat may need new propeller shafts, gearboxes or even transmissions. A qualified installer can point out all of these things and identify unexpected costs.

As for Kiser, he still has one decision before he makes the switch: Stay with inboards or go with a jack-shafted sterndrive configuration after reinforcing the boat's transom?

"I'm still thinking about it," he told me. "Some of the mechanics I've talked to say the jack shafts will let me run faster and get into shallower water. That means more fish, and that's the ultimate goal."

Price Point
How much we talkin'?

Here are the basic costs to re-power a 35-foot sportfisherman with diesels.

Two 315-hp Yanmar diesels @ $20,500 ea. $41,000
Labor 6,000
Parts and Hardware 7,700
6% Sales Tax 3,282
Total $57,982


Note: Dollar amounts are rounded.

Olympian Props
A new system adds agility to power.

MOD PODS: Zeus uses through-hub exhaust to reduce noise and fumes.
Photo: Courtesy of Cummins Mercruiser

Project Zeus, a pod-drive system using Cummins MerCruiser Quantum diesel engines, is the latest wrinkle in marine propulsion. Introduced at the Miami International Boat Show following 15 years of development, Zeus uses independent drive vectoring to provide a seven-percent-faster top speed and 30-percent-better fuel economy at a higher cruise. Equipped with a companion joystick control, the system will be available in the 2008 model year.
— D.L.