Lining Up the Repower Project
Getting the owner of an older sailboat to spend the money on a brand new diesel auxiliary is a challenge for many marine service businesses. Often the costs involved in the purchase and installation of a new powerplant carries a bill that can make most recreational boaters blush and run away. Some vessels, however, are built for the long haul and replacing the diesel engine on an otherwise sound mechanical vessel can extend the life of the boat at a fraction of the cost of the replacement of the entire boat. Newer marine diesels are also more fuel efficient, smoother, quieter, lighter, and pack far more horsepower into smaller packages.
A boat designed for offshore passagemaking shouldn’t rely on a rusty old clunker engine to transit the ocean blue and that was just the case when John Nassichuk of Raven Marine in North Vancouver, BC was tasked with installing a new power plant into “Northern Dancer” a 43’ Hans Christian ketch. The boat’s 25+ year old Nissan diesel had served the boat admirably, but the owners wanted to do more long-distance cruising and needed dependable power. As an authorized Yanmar installer and service center, John recommended the 4-cylinder Yanmar 4JH-4-TE for the job citing a smooth-running, rubber-mounted engine would efficiently drive the heavy hull form of the Hans Christian. Due to the full keel design of the vessel, the boat had an extremely long propeller shaft that extended from the diesel amidships all the way aft to a propeller aperture at the trailing edge of the keel. Supporting the shaft was a cutlass bearing aft and a rigid pillow block several feet aft of the gearbox.
Since the original Nissan diesel was solid-mounted to the hull and the new Yanmar unit was mounted on flexible mounts, there were concerns about being able to support the industrial style prop shaft where it coupled to the new gearbox. Additionally, Yanmar stressed the use of Yanmar’s flexible motor mounts when repowering to validate the warranty of the motor. To provide adequate prop shaft support, the rigid mount pillow block bearing would need to remain in place, but how then to properly align the shaft to the rubber mounted transmission? The solution came in the form of a free floating Powertrain CV joint coupler distributed by Thermoboat in Sydney, BC. The coupler was bolted inline aft of the gearbox and provided support to the shaft without the need of building a separate bulkhead mounted CV joint.
“This was a far more economical solution,” says Nassichuck. “Building a bulkhead and then mounting a rigid CV Joint to support the shaft was going to be really expensive. This worked out great.”
When asked if there were any drawbacks to the Thermoboat Powertrain Coupler compared to a conventional shaft coupler, John made sure to stress the importance of making precise measurements when cutting or fabricating the prop shaft. “A standard 5” rubber coupler gives you a few inches of leeway when doing a shaft install. The Powertrain coupler is so small and compact, you have to measure out the shaft just right.”
Available in three sizes, the self-aligning Powertrain Coupler is designed to withstand the torque loads of engines in excess of 700 HP and can allow for up to 8 degrees of shaft deflection without requiring a supporting bulkhead mount. Once the prop shaft was properly cut and the new diesel lowered into place, it took just a few hours to finish hooking up the shaft and tightening the remaining bolts throughout the diesel. While this installation was done as part of a repower project, Nassichuk estimates that installing the coupler on diesels already in the boat would likely take far fewer hours than if a bulkhead coupler was utilized. Also John noted that the coupler comes pre-lubricated from the factory and requires little or no maintenance during the life of the powertrain.
With a new diesel in place and the prop shaft hooked up, the Northern Dancer’s owners took off on their first cruise in years without worrying if the engine would give up on them when they needed it most. And while a new power plant wasn’t the least expensive modification they’d ever done to the boat, it was one of the best values when it came to peace of mind and reliability.
By Chuck Gilchrest
