Story And Photography By Steve D’Antonio
It’s a subject that gets far too little attention: alignment of a vessel’s running gear, the propeller shaft, bearings, and engine. Yet, all too often I encounter poorly aligned shafts on both new and used vessels alike. Having inspected and/or supervised the correction of many such shafts, I have a few ideas on how and why this occurs and how new installations and repairs should be carried out.
While it encompasses all running gear components—from motor mounts to cutless bearings—from this
point forward I’ll refer to the process simply as shaft alignment. Insult is added to injury by the fact that shaft
misalignment is insidious; contrary to popular belief it doesn’t always offer up clues, at least not obvious ones.
Indeed, vibration can be an indicator of shaft misalignment; however, I’ve sea-trialed many vessels that ran
smooth and vibration-free only to learn upon haulout that the running gear was seriously misaligned, so much
so in some cases that I was unable to turn the propeller and shaft even when applying 145 pounds to the effort.
I know that I applied precisely this much effort because my feet were off the ground. I’ve encountered folks in
the industry who write this off with responses such as “dry bearings” or “all boats are like this when hauled, it’s
different when they are in the water.” Nothing could be further from the truth. Rest assured, with “wet” bearings
(they can be lubricated with diluted dish detergent, but never oil or petroleum-based lubricants) shafts should
turn with no more effort than one would use to lift a carry-on suitcase and in some cases, just fingertip pressure.
Why is misalignment an issue if the symptoms are often so subtle? Shaft misalignment causes increased wear
to both shafts and cutless bearings and it may also lead to wear of other components, components that are
neither designed to support nor make contact with the rotating shaft. The primary area of unintentional contact
affected by misalignment is the shaft log, the tube through which the shaft passes as it exits the vessel. This drag
increases fuel consumption and damages both shaft and log. In a few cases it may lead to vibration, although
that’s not necessarily a given.
Some have accused me of being fixated with shaft alignment, or at least proper shaft alignment, saying that I
take it to an extreme. I categorically reject that notion. Fixation doesn’t begin to describe how frequently I think,
write, and sometimes dream about this aspect of boatbuilding and repair. Obsession is a more apt description.
I spent a good part of my professional career studying and honing my understanding of this skill. Thus, when I
received an email from Chris Brown, shaft alignment specialist and proprietor of appropriately named Straight
Line Marine in Ft. Lauderdale, I immediately recognized in him a kindred spirit. His note was in response to
a column I’d written regarding propeller nuts and the order of their installation, a suitably esoteric subject that
signaled to me that this guy was not only a detail-oriented gearhead, he walked the walk when it came to
running gear. It didn’t take long for the dialog to progress to an invitation for a tour of his shop, which I readily
accepted. Straight Line Marine, also known as High Seas Yacht Service, is located at Lauderdale Marine Center. I