Chain Reaction

Anna's new cutlass bearing, stern tube and
 repaired bronze flanges ready for installation.

Vibration. Catalyst of chain reactions. When a diesel engine's four rubber motor mounts vibrate, while the engine works hard, the adjustable fasteners on the motor mounts, which hold the engine in precise alignment with the driveshaft can loosen, even unwind and fall off if they are not locked down properly. And when this happens, an unfortunate chain reaction of events may be set in motion; none of which does the boat any good at all.

Misalignment of the engine can result from a failure of the motor mounts to hold the engine in this precise alignment with the axis of the driveshaft. Damage to the driveshaft and any of the fittings between the transmission gear box at the forward end of the driveshaft, and the propeller at the opposite end is likely when the alignment is severely off axis.

The driveshaft fittings on Anna include: the shaft coupler; the DriveSaver bearing; the PSS shaft seal; the internal shaft log bearing; the stainless-steel shaft log; the cutlass bearing; and the exterior log bearing. Additionally, the structural integrity of the fiberglass that surrounds the stern tube may be affected. So, in our hypothetical chain reaction, there come into play a lot of dominos that can fall as a direct result of vibration.

Driveshaft and new DriveSaver bearing connected to transmission.

Now it wasn't our intention to test the validity of the chain-reaction hypothesis, but there it was: vibration had set off the domino effect on Anna. The first of the symptoms was subtle and provided us with the initial red flag: a slight vibration that could be felt over a specific range of RPMs when the engine was under a load. But all engines vibrate to a certain extent. So it wasn't conclusive evidence that something was wrong; it was just evidence that something was different than what we were used to.

Less subtle signals, later, confirmed that something wasn't right: an unfamiliar growling, low-pitched metallic noise, which came and went for a few seconds at random intervals; a strong, burnt, synthetic smell that lasted for a couple of days, before dissipating, occurring more frequently in the ocean swells; a faint, high-pitched ringing sound that occurred randomly, coming from the area around the shaft log; a small reduction in our velocity, or speed through the water, when motoring within our normal RPM range; a prop shaft that was extremely difficult to turn by hand while the transmission was in neutral. Technically referred to as 'shaftbound', the prop shaft couldn't be turned by hand with relative ease; a mist of steam emanating from the rubber bellows of the PSS shaft seal, most likely caused by overheating (due to excessive friction within the shaft log). Even the cold seawater, which passed through the rubber PSS bellows became excessively hot to the touch; and finally, an electric bilge pump that triggered on more frequently than usual, because seawater was slowly entering the bilge from the area surrounding the stern tube (difficult to spot at first, since the leak was mostly hidden by the PSS bellows obstructing the view).

The cause of the symptoms was an enigma at first. The driveshaft itself looked undamaged and 'appeared' to be aligned -- at least, it had no significant wobble when it turned. But, in fact, the shaft was prevented from rotating freely due to the pressure that the engine had placed upon it. In essence, it was shaftbound, which appeared to dampen the wobble. Regardless, the driveshaft wasn't aligned square to the engine. The engine had dropped, vertically, about one inch from its original aligned position, after the motor-mount adjusting nuts had vibrated loose. Three of the four motor-mount studs were missing their locking nuts. They had vibrated off. The motor mounts had bottomed out on the aft end of the engine. They were no longer supporting the weight of the engine, or holding it in precise alignment to the driveshaft. A good alignment is measured in thousandths of an inch. Our alignment was now off by about one whole inch. A world of difference.

The aft end of the engine was now supported solely by the driveshaft. Bad news. This meant that the bearings and coupling and stern tube were all trying to compensate for the job that the motor mounts were intended. Not really something that they could do for very long. Nor something that they could do effectively. A driveshaft that is grossly off axis will result in metal-on-metal fatigue. The hard, stainless-steel driveshaft was slowly grinding down the supporting, bronze shaft log bearings as well as the thinner, stainless stern tube, which passed through the bronze shaft log bearings. Heavy, shaftbound friction was taking its toll. The growling, ringing, leaking, burning and smoking symptoms now made sense.

Stainless steel is a hard metal; harder than bronze. Friction had worn down the softer metal components, paper thin, where the driveshaft had made contact with the bearings that it passed through. Damage was also noticed inside the cutlass bearing, as well as the PSS rubber o-rings and bellows, and the shaft coupler. The integrity of the area surrounding the shaft log (that is, the fiberglass housing where the stainless stern tube passed through) was breached as well. And it allowed seawater to find a path of entry into the boat's bilge, just below the damaged shaft log.

Damaged interior threads on exterior log bearing.

Damaged interior log bearing flange, note worn down lip.

Damaged stainless steel stern tube.

Damage to log bearing and interior fiberglass-wood laminate.

We believe that the first obvious symptoms of drivetrain trouble occurred in the ocean swells, off Cape Mendocino, on a run from Eureka to San Francisco. We limped under the Golden Gate Bridge and into the Gate 5 area of Sausalito's working waterfront a couple days later. We had our suspicions of drivetrain trouble confirmed by a very experienced diesel mechanic that really knew what he was about. The first step in resolving the problem was to realign the engine, while Anna was still in the water; and after that, to lock down the adjusting nuts with locking washers sandwiched in between a set of lock nuts, so that the loosening effects of vibration were minimized. 

Motor mount after readjustment.

The second step was to remove, inspect for damage, and replace the damaged fittings on the drivetrain, while the boat was on the hard (seawater was leaking into the bilge from the area around the shaft log, and the area needed to be dried out). Finally, we needed to repair any damage to the structural integrity of the area surrounding the shaft log.

Stern tube's fiberglass housing .

After completion of the alignment we hauled the boat at the neighboring yard, removed the driveshaft and attached fittings, dried out the damaged area surrounding the shaft log, and had a new, stainless stern tube fabricated by a local machinist, who also repaired a section of the bronze, interior log bearing, which had worn away. The voids and damage to the fiberglass, around the shaft log were beefed up with G-10, a structural epoxy board, which was cut to fit the tight space on the interior wall, where the driveshaft comes through the shaft log to connect with the transmission. 

G-10 epoxy repair to interior shaft log housing.

G-10 repair and interior log bearing installed.

A new cutlass bearing was fitted to the stern tube after damage was discovered on the existing bearing. The driveshaft coupler was fitted with a new, stiffer DriveSaver bearing, and a new PSS shaft seal was fitted to replace the old one, which was worn and due for an upgrade.

Old PSS assembly removed.

Repaired bronze,  interior log bearing flange.

New stainless steel stern tube ready to be installed.

All boats have defects of one kind or another. Some critical, some not so much. Some are discovered before they cause problems, some not. The bottom line is that Anna's structural integrity, in the critical area surrounding the shaft log will now be unquestionable. And, of course, the engine will be perfectly aligned, once again. In our routine engine maintenance, every 100 engine hours, we'll check to see whether normal engine vibration has loosened the motor-mount fasteners. If it has, we'll be sure to tighten them up before they can trigger another chain reaction.

New DriveSaver bearing installed on shaft coupler.

New PSS assembly installed on G-10 repair job.

Driveshaft reinstalled.

Reattaching the bonding strap to rudder assembly.

Drivetrain assembly completed and installed.

Thanks to what might be described as a forensic analysis, of the root of Anna's little chain reaction, by some of the talented and resourceful people who helped us out at Sausalito's working waterfront, off Gate 5 Road, Anna can now continue on her way with the confidence that her repairs were sound. It took us two weeks in the yard to sort out all the complications and complete the repairs, but they were two weeks well spent.

We figure that if we take good care of Anna, she will take good care of us. What more could we ask of each other? We left the yard and put Anna back in the water where she belongs. But as we carry on with the voyage we'll continue to make no distinction between repairs on the hard (or in the water), and long-distance sailing. They are both intrinsically linked. Sailing and repairs have always gone hand-in-hand for us, and we don't have any illusions to the contrary. It is what it is, and we accept that. Besides, living up in the air, at the yard for two weeks, makes life back on the water that much sweeter.

Sausalito's Richardson Bay, view from boat yard.

We'll now sea trial Anna, while spending some time sailing around S.F. Bay. After visiting with friends and family here we'll head further south, once again. Probably by the end of October. As always, weather drives our decisions about when and where to go. But roughly, our plan is to keep sailing south until the weather gets balmy. And then, continue even further south, until the weather gets chilly. That's our plan, and we're sticking to it.