As the Transportable Trawler project takes shape, one of the first decisions was the choice of power. Actually, we've been thinking outboards from the start. By combining a light composite build with a easily-driven hull shape, we're predicting some pretty impressive performance numbers from a pair of 60 hp four strokes. These motors are thrifty, low-maintenance, and cost-effective. Mounting them on the transom frees up a lot of real estate in the bilge, and should provide whisper-quiet operation at the helm. At the end of the day, you just tilt them out of the water, and save for the occasional fuel filter change, you can get up to 100 hours between services.
All that being said, it's possible to make a reasonable case for inboard diesel power, and several folks have already voiced preferences in that direction. Mirage has a lot of experience with diesel propulsion, not only in our full-displacement N and GH trawlers, but also in our performance sport fishing line. In fact, our 32 Center Console remains one of the most fuel-efficient canyon runners on the market, delivering an impressive 3.5 mpg at 35 mph on a single Volvo D3. So yes, diesel certainly has it's place in our lineup.
But we don't think that place includes the new Transportable Trawler. For several reasons. It's easy to rule out a traditional shaft-drive inboard as it would require a higher cabin sole, and a correspondingly taller deck house. The hull would also sit higher on a trailer, be more difficult to launch, and draw more water. A diesel also adds extra layers of complexity. In addition to the daily fluid checks that should be part of any diesel maintenance plan, there are intake hoses, exhaust systems, belts, shafts and engine mounts to monitor. And should you wrap a line around the prop, or ding a blade, well, somebody's going swimming.
The I/O option addresses some of these objections, and it wouldn't be difficult to tuck a Volvo D3 under this boat's cockpit. One problem with this install is weight, and weight reduction is one key to this boat's success. Even high-performance turbo diesels can't match outboards on a power-to-weight basis, and the Volvo would be more than twice as heavy as the four stroke outboards. You could also count on spending more than twice as much for the diesel and, at the end of the day, I/O drives still require more care and maintenance than outboards.
That just leaves a couple of concerns that traditionalists continue to raise with regards to outboards—though we feel they are pretty much non-issues. One is the ethanol content of most gasolines. Modern outboards are engineered to accommodate ethanol blends, and there are plenty of available additives to stabilize stored fuels. Also, fears of gasoline's greater inflammability as compared to diesel are over-rated, especially when dealing with outboards.
13 to So yes, we're going with a pair of four strokes on the transom. And though it's very early in the game, we'll take a chance and toss out a few benchmark performance numbers. Understand that these are based purely on educated conjecture, and assume that we will bring the final boat in at around the 6,500 pound dry-weight mark. We're considering Suzuki's DF60s, which should push this boat to a cruise speed of around 14 to 15 mph in calm water, when running between 4,000 and 4,500 rpm. Based on Suzuki's own test data, that would result in a fuel burn of 2.3 to 3.1 gallons per engine per hour. Even if we miss that mark by a bit, we're still looking at nearly 3 mpg at fast cruise, and a range in excess of 400 miles on the standard 150 gallons of fuel. Throttle back to traditional trawler speeds of eight knots, and you double that range with a bit to spare. Plenty to get you to the islands.