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Engine Insight

Is a repower job right for you? Here's how one boat owner tackled the question.

"For me, it was always wanting to be on the water," says Bob Dunn, captain and owner of Moonshadow, a 29-foot Ocean he charters out of Penna's Marina in Beach Haven, New Jersey. "And as long as I was making that decision, I decided I was going to do it right and within my means."

Dunn is a charter fisherman who along with his son Bob, Jr., operates his boat from spring to late fall. While most of his business comes from half-day family charters, he looks forward to canyon runs for white marlin and tuna during the summer months.

He says he first saw Moonshadow in 1998 and decided she was the perfect vessel for his needs. "She had a pair of 350-hp [gasoline] Crusaders with very low hours on them," he recalls. "The boat cost me $65,000, and I fished her all that season and was getting killed on fuel costs. When I put her up on the hard after my second year, I knew I needed a pair of diesels if I was going to make things work."

Dunn came to his decision with engine-swapping experience already in his wake. He'd replaced the 85-hp diesel in his previous boat, a 29-foot Prairie trawler–which he had for 20 years before buying Moonshadow–with a 200-hp Perkins diesel. He did his homework all winter, attending most of the boat shows and finally decided on a pair of 300-hp Yanmar 6LPSTEs. "Price, weight-to-horsepower ratio, engine size, range and fuel consumption, application, trade-in for my engines, resale value, and finally reputation were key factors for me," he says.

Dunn says the price tag for the Yanmars came to $38,751 (with Crusader trade in), including Hurth 630A1 2:1 ratio down-angle gears (unlike the Crusaders, these diesels would be installed flat), engine mounts, 80-amp alternators, couplers, wiring harnesses, L-type mixing elbows, and freight.

With that decision out of the way, Dunn sought out a yard to do the installation. "It's crucial to get the right team for the job," he warns. "Time is money, and when you're a working stiff like me, $75 per hour for a decent mechanic takes on more meaning. The last thing you want is someone without a plan." For him, the decision was easy. Steve Westberg, Penna's yard foreman and head mechanic, had done the Perkins exchange on the Prairie, and Dunn had been pleased with the way that job came out.


To keep costs down, Dunn did most of the grunt work, unhooking the old engines, readying the wiring harnesses, hoses, and Racors, draining the tanks, and doing some minor fiberglass and duct work. Once the Crusaders were removed, Westberg fashioned new beds, boxes, and engine vents.

"The boat was originally set up for diesels, as they were offered as an option," says Dunn, "so the tanks had return lines and the raw-water intakes were large enough. I also lucked out on the running gear. According to Yanmar, I needed inch and a half shafts, and that’s what I had." He says that getting the new engines to fit the existing beds is one of the major problems with a repower job. "It’s not just a matter of cut here and take some off there until you’ve got a fit," he points out. "If your guy second-guesses, not only are you wasting time, but you could be opening yourself up to a lot of trouble later on." Not only did Westberg modify the Ocean’s stringer system to accept the Yanmars, but he even customized a gutter system around the new engine boxes so that any water accumulating there would run out.

Dunn says actual installation time amounted to about two weeks, although Moonshadow was tied up for most of the winter because Westberg was busy with other work, the weather didn’t always cooperate, and Dunn was in no hurry to get it done. All told, Dunn says fiberglass work amounted to 53 hours, removal of the old engine boxes and fabrication of the new ones took 14 hours, and 18 hours were required to install the new engines, including connecting the new gauges. "The yard bill came to $8,028.43 just as we hit the starter button," he says.

Were the results worth it? Dunn reports he was averaging about 26 gph with the gasoline engines at a cruise speed of about 20 mph at 3200 rpm. At that rate he had a 145-NM range based on his 210-gallon fuel capacity. With the Yanmars he says he’s burning less than 20 gph at a cruise speed of almost 30 mph at 3350 rpm, a speed I confirmed with our Stalker radar gun and a GPS when Dunn took me for a ride. That works out to a nautical-mile range of 247. When he bumped the rpm to 3600, Yanmar’s recommended cruise speed, I clocked a speed of 32.4 mph. "In addition, I’ve got about a 300-mile range on the boat, where before [with the gasoline engines] I doubt I had half that," he laughs as he admits to once running out of gasoline in the C&D Canal on a trip from Annapolis to New Jersey.

A key concern in the success of this installation was the choice of props. Dunn wasn’t sure the original props–three-bladed, lightly cupped 20x24s–would do the job, but felt that at the very least he could use them as spares. (A dinged prop can result in expensive down time for a charter boat.) Besides, he wanted to make sure he had the right props for the new installation. "Given all the work I put into this project," he says, "the last thing I needed was the wrong props."

Dunn ended up purchasing a set of 19x22 ISO Class I (high-accuracy), four-bladed Austral props, also slightly cupped, for $1,600, from Steve King at Black Dog Props of Stevensville, Maryland. "I heard a lot of good things about Prop Scan, and Black Dog had been involved in several repower jobs with Yanmars and had all the power curves for the engines," he explains. "When they ran the numbers through the computer program, it came up four-blade."

I asked Dunn if we could compare the three-bladed props with the four-blade ones, and he agreed (see charts above). Our average of four runs for the original wheels was 29.2 mph at 3350 rpm, his usual cruising speed. When we pushed the engines to 3600 rpm, Yanmar’s recommended cruise speed, the average increased to 32.4 mph. With the Australs installed, I measured almost the same speed at 3350–29.7 mph–but our top-end average was 33.9 mph, a solid mile and a half faster. More important, however, was the overall increased smoothness out of the hole as well as during cruising speeds.

Dunn figures he’s invested a total of $113,379.43 in the Ocean, which he guesses now has a value of around $125,000. (He says he found a similarly equipped Ocean 29 with an asking price of $129,000 on the Internet.) Little wonder that while admitting that repowering is not for everyone, Dunn sums up his project this way: "As far as performance, economy, range, and safety are concerned, I’m 100 percent satisfied."

If you rack up a lot of hours annually, repowering may make sense. If you’re considering taking on such a job, follow Dunn’s advice and do a lot of research. Understand your boat’s limitations and what is practical for your needs, rely on a mechanic with a solid track record in repowering, and settle on a firm work schedule before you sign a contract. The more you know beforehand, the less you’ll worry about come launch day.

Moonshadow Charters Phone: (609) 709-4026 or 492-8659.

Penna’s Marina Phone: (609) 492-0191. Fax: (609) 492-1954.

Prop Scan USA Phone: (877) 767-7226. Fax: (757) 485-7839.

Yanmar Phone: (847) 808-2213. Fax: (847) 541-2161.


Boat: $65,000.00

New engines: $38,751.00

Labor: $8,028.43

Props: $1,600.00

TOTAL: $113,379.43

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