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An Update and a Mystery

Airship Goes to Alaska

Alrighty gang, here's an update on our mechanical issues. I don't even think there will be pretty pictures this time, so if boat mechanical issues are not your thing, feel free to skip this post. 🙂


As you may remember, we had a little excitement at sea last week. Our dripless shaft seal overheated while running at higher cruise speeds for an extended time. (Here's what a dripless shaft seal is and does.) We smelled a burning smell and the boat shuddered and slowed down. We put the boat in neutral (in 5 foot seas) and found the smell coming from the shaft seal. We tried carefully putting the boat in reverse, seemed okay, then forward, seemed okay, so we kept making slow idle progress forward as we inspected things. The seal was hot but cooled down quickly as we continued at a lower rpm. We proceeded on to Juneau (three more hours), checking the seal continuously for any signs of heat. 

Once in Juneau we hauled the boat out to inspect the shaft and prop to make sure there was nothing wrapped or any damage. Surprisingly, everything seemed perfect. There was nothing wrong, and no sign that there ever had been anything wrong. The surface of the prop shaft had the usual greenish patina/moss. (If something gets wrapped around the shaft (fishing line, for instance), it polishes the shaft to a nice shiny stainless steel gleam.) The prop and shaft turned easily and there was no play in the shaft when lifting it or pushing it side to side.

Since everything on the outside of the boat seemed normal, we turned our attention to the inside of the boat. We'd been suspecting for a while that we might have a problem with shaft alignment (some vibration we didn't think was normal, loose bolts on the shaft coupler…things like that). We had a local shipwright check our alignment and it was definitely off. He aligned it for us and we got to learn all about how the engine mounts are adjusted to move the engine and transmission into alignment with the shaft, and how to check the alignment ourselves in the future. Neat!

We were still a little worried though, because although things seemed okay, we hadn't found the "smoking gun" that had caused our problem out in Lynn Canal. The best guess at the time was that it might have been a weird combination of three things: (1) the slightly misaligned shaft causing more vibration and friction than normal, (2) running the engine at high rpm for several hours on end, exacerbating problem (1) above, and (3) cavitation caused by the following seas we were running in when the overheating happened, keeping sea water away from the bearing parts it was supposed to be cooling. (Spoiler: turns out this was completely wrong.)

So, we took the boat out for a sea trial to see if things were okay now. In our extended testing at all different rpms while watching the listening (and smelling) the shaft, shaft seal, etc., everything stayed cool and nothing seemed off – until we tried the high rpm test again. At 65% power (3200rpm), the shaft seal bellows inflated like this:


This is really, really bad because if that bellows ruptured, sea water would be entering the boat quickly. This can cause boats to…you know…sink and stuff.

So, if at this high rpm this is what the bellows was doing, then for 3+ hours running in Lynn Canal the other day, the inflated bellows could have been putting undue pressure on the shaft seal (the carbon collar part that presses and rotates against the stainless steel collar plate) and causing the seal to overheat. The shuddering slow down we felt therefore might have been the shaft seal dragging at high temperatures.

After talking to PYI (the company that makes the shaft seal), it sounded like the raw water pressure from the engine was too high for the shaft seal. The seal was supposed to have 1-2psi for normal operation, and no more than 10psi. At high RPMs, the raw water pressure could be over 20psi. Normally though, the pressure would not build up that high because the water would be able to flow easily through the cutless bearings out into the sea.

Here's what a Cutless bearing looks like. The shaft goes through the bearing, and the grooves allow the flow of cooling and lubricating water to the shaft:

Screen Shot 2015-08-12 at 5.44.47 PM

We installed a valve in the raw water feed line so we could reduce the flow of water to the seal.


This worked…the seal ran cool and the bellows didn't inflate. But now the seal leaked quite a bit. We later learned while troubleshooting the leak (and looking at survey photos of the shaft seal from when we purchased the boat), that the inflation incident had pushed the rear of the bellows a little over an inch aft on the fiberglass tube, so the bellows was no longer properly compressed.

We readjusted the shaft seal per factory installation instructions and…no more leak. (Note the two dots on the stern tube on the right…those are set screws for the forward Cutless bearing. In the inflated photo, the bellows is pressed all the way up against those set screws. This is how it should look…well, almost…ours now has a larger gap between two folds of the bellows due to the prolonged inflation):


We sea tested with this new shaft seal adjustment for several hours. The seal ran cool and smooth and the bellows did not inflate, but we had to turn the water flow down to just a trickle to stop the bellows from inflating at higher RPMs. This meant we still had a problem…not enough water flowing through the Cutless bearings.

When we disconnected the cooling water feed line from the shaft seal, we noticed that only a tiny amount of water was leaking back into the boat through the Cutless bearings (there should have been a pretty good flow), so we decided to have the boat hauled out (again) to see if we could manually clear the Cutless bearing grooves.

Once hauled out, we removed the prop and found that the grooves on the outside Cutless would only allow us to poke a stainless steel rod in about an inch and a half before they ran into some kind of gritty crud.

We then disassembled the shaft seal inside, and when we removed the bellows, a large chunk of something black fell into the bilge. The same black something was melted and burned around the outside of the inner Cutless bearing. Small pieces were wedged into the grooves, and much larger chunks were still rattling around inside the bellows.


We dug all the pieces out, and it looks like they used to form some sort of a hard black plastic or rubber seal or collar, about the same inner diameter of the shaft. (You know that part in CSI where they bring all the pieces out and puzzle them together on a giant table to try to figure out what they used to be? That's what we did, but without giant light table or slick soundtrack.)


The pieces are consistent and have a specific complex design, and the pieces match up with each other. (And they all smell exactly like the burning smell we smelled during the event the other day.) There's a lip, and some grooves. Here are some close ups:



All the parts of the shaft seal looked fine and were present and accounted for, so nothing in the shaft seal gave us a clue to what this mystery object was or where it came from. These (quite large) pieces were INSIDE the bellows, and there's simply no way anything this size could get in there from anywhere else. It had to be in there when the shaft seal was installed. (That's right, it's coming from INSIDE the house!!)

Thanks to some super expert sleuthing, we now believe that this extra part was in fact a lip seal from another kind of shaft seal. Yep, that's right. A part from a completely different kind of shaft seal, was inside our shaft seal.

This mystery part apparently caused our whole shebang. But the plot thickens. This is the original factory-installed shaft seal. Our boat is two years old and has only about 1000 hours on it, and we've been told that this shaft seal has never been removed since the boat was new. So, the source of the foreign part remains a mystery. Was it like when a surgeon accidentally leaves a tool inside the patient, and they find it years later during a simple x-ray for abdominal pain? We may never know.

We've now pulled both Cutless bearings (without having to remove the shaft or the rudder, hooray!) and both of them are completely destroyed. (Normally, these last for years and years and thousands of hours. You should inspect yours periodically though when you haul your boat out. Here is why:

Here's the inside of a new one:


And here are the two we just pulled out of the boat:



We were only able to find one new Cutless bearing locally, but the Nordic Tug factory had some in manufacturing stock that they could sell us and ship to us right away (as well as a new PSS shaft seal), and we should have those parts by Friday (just in time for the Golden North Salmon Derby here in Juneau, when everyone will be out fishing, not working on our boat). So probably on Monday, we'll replace both Cutless bearings, install the new PSS shaft seal, do some double and triple checking of all the connections, bolts, adjustments, and alignments, and then do a lot more sea testing around here to make sure we're all good before heading south. 

This brings up an important point for those of you who own things like boats and RVs (or would like to):

A boat is NOT a car.

Unlike the cars we all drive, boats are not built in multi-billion dollar factories by precision robots. They are not the product of hundreds or thousands of man-years of engineering, development, and testing. They are not sold in enormous quantities for worldwide distribution and supported by thousands of expert-in-one-brand technicians. 

Each boat (or RV) is a work of art — individually and lovingly hand-crafted by living, breathing, hard-working, fallible human beings. Every boat made has flaws, mistakes, compromises, and other issues that we would never expect to find in mass-produced products like our cars. 

You cannot expect to hop in your boat, turn the key, and buzz around the waterways without a care in the world, stopping at the Jiffy-Lube a couple of times a year for ten minutes of minimal routine maintenance. A boat requires care and understanding. Each boat has its own individual personality with its good and bad traits. 

If you’re going to have a long and happy relationship with your boat or RV, you need to really get to know its quirks and traits. You need to look deep into its eyes, take long walks together on the beach, and have intimate conversations about life, the universe, and Cutless bearings. You need to understand how the various systems work and interact and fail because yours WILL break down sometimes, and those breakdowns will almost never be simple “drop it off at the shop and pick it up the next day with the franistan replaced” kinds of events. You will be out there at sea or in a remote boondocking location – far from the nearest factory-authorized repair station, and your family's safety may depend on the quality of your relationship with your wonderful machine. 


  1. That’s quite a haul! Are those vacuum bags? Also:, eh? Do tell… 🙂

    • Yep, vacuum bags. (We’ve had for a while…it points to and I’m in the process of making that go the other way.) 🙂

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