Prop shaft / stern tube question

[HJ51]

Question:  is there a seal or gasket of some kind BEHIND the cutlass bearing itself on the prop shaft (i.e. as the very last thing on the stern tube before the rest of the shaft leads to the prop)?

My boat is in the water so I can't get a great visual going underwater, but there appears to be a gasket or seal of some kind that goes around the shaft and fits up into the stern tube.  I felt some vibration in the prop shaft and when I went under to inspect found that this seal/gasket had slid down the shaft toward the prop.  I slid it up and pushed it into the stern tube as best I could and the vibration seems to have stopped.  I am hoping this is unrelated to (and not part of) the cutlass bearing itself.  The part that I was able to slide back up felt like it was made of rubber or similar.  And full disclosure I had a line get wrapped tight around the shaft a few weeks ago that I cut off.  Can anyone enlighten me on this?  Thanks in advance!

[wes]

No, the cutlass bearing is the only thing in the stern tube. It consists of a bronze outer tube bonded to a rubber inner bearing surface. Sounds like the rubber part has detached. If so you need to replace the whole cutlass bearing. This will almost certainly require a haulout. Sorry!

Wes

[HJ51]

Wow that is reeeeally bad news.     Plus right in the middle of family summer boating time.  But valuable information nonetheless, thanks Wes.

A couple more questions now:

1.  How do I source that part?  Is it a Yanmar thing (I have a 2GM20F)?  A Com-Pac part? 

and

2.  Since I assume the prop shaft is coming out is there other maintenance I should be do with this "opportunity"?   Stuffing box?  Something else?  I am unfamiliar with this part of my boat (and therefore will be getting it serviced professionally). 

[wes]

If your prop shaft and tube are the same size as my 1988 boat (important to verify!) the shaft diameter is 1" and the shaft tube inside diameter is 1.5". You can order the cutlass bearing from Defender.com, their part number 305916. They have them in various sizes to fit most boats.

After I pulled my shaft, I took it to a prop shop and had them balance the prop, check the shaft for trueness, and machine the transmission coupling for the correct friction fit on the shaft. If I had it to do over again, I'd buy a new split style coupling.

I also replaced my traditional stuffing box with a dripless PSS Shaft Seal. It's pricey (around $225) but forever eliminates the need for repacking and adjusting the stuffing box. It's standard equipment on expensive new sailboats these days and I've been very happy with mine.

Wes

[HJ51]

I ordered a cutlass bearing from Com-Pac and hauled my boat out to do the repair and discovered to my amazement that the bearing was perfectly fine.  It turns out that the circular "rubber" piece coming out of the end of the stern tube was the rope that had wrapped around the shaft, melted from the friction, and reconstituted as a round, gasket shaped piece of plastic. 

Here's a picture of it after I cut it off.

https://photos.app.goo.gl/JexAh6HEXZHaYm198

and here are a couple of shots of the prop shaft and stern tube which show the cutlass bearing in good shape.

https://photos.app.goo.gl/N7C7bGw4meLYF1Vd8

https://photos.app.goo.gl/Xnts5oehxT4MmxtZ7

This was a very happy (and inexpensive) outcome.  Since I didn't even drop the mast, I was able to just cut the melted plastic ring off and put the boat right back in the water.

Question:  does everyone's prop shaft have the bolted on weight shown in my last picture?  Or is that something that was added by a previous owner, possibly to compensate for a balancing issue?

[Andre]

I have no inboard experience, outboards only, but I think the "weight" you're referring to is a sacrificial zinc.  And if that's what you're referring to, it's absolutely critical to the mettalurgical integrity of the shaft, prop, etc.  Yours seems ok but be sure to check it (them?)  at least a couple of times a season.  Especially in salt water and in marinas (versus moorings).  Cheap insurance!

I'm sure others here with far more knowledge than I have will chime in.

Andre

[HJ51]

Ok, wow, after Googling I feel a little foolish because yes that is exactly what it is.  I don't know much about that end of my boat (which is probably obvious now).  How often do I need to change that guy, and should there be more anodes on the prop system like on the rudder?

[BobK]

You only need one on your prop shaft.  You should check it at least twice a year.  How fast it is used depends on fresh or salt water, how much the boats around you leak electricity into the water, and how much time you are plugged into the dock power.  You can google anode usage to get more information on this. 
I don't plug my boat into the dock power because too many boats around me in brackish water leak electricity into the water.  I get a full year before I change anodes  where the boats around me that are plugged in and share a common ground have to replace their anodes 2-3 times/year due to surrounding boats leaking electricity.
BobK

[moonlight]

Anodes should be changed:
- when 50% wasted, or
- when they become inactive due to surface fouling.

Case #2 is often discovered if you see little bore holes in them, almost like worm holes or bee holes but the size of a pencil POINT.  This is active metal tunneling out through a channel through the inactive surface metal.

Change them annually.  PERIOD.

Don't change them, and your shaft will look perpetually fine anyway.  So will the outside of the prop, until it starts pitting like the worm holes above.  Then it's too late.

Then one day, you'll fracture off a blade of the prop.  It'll be bright pink inside.  Because all the zinc has leached out of the bronze prop, leaving just the copper, because there wasn't a "zinc" anode on the shaft.  If in brackish or even salt water, search and get an aluminum anode; it is a step farther down the galvanic scale and will provide better protection.  If in pure fresh water, you may use magnesium for the same reason.  But magnesium in a more conductive electrolyte (i.e. brackish/salt water) will burn like gasoline on a fire, you'd be putting them every week or month.

Dis-similar metals in an electrolyte is how batteries are made.  Bronze props on stainless shafts is one case.  Stainless props on aluminum outdrives are another...

I was by a buddy's shop today; a lady had come by seeking to get her 2004 boat running and sold.  Twin engine power something had been sitting behind the house ...

They took batteries, it started right up.  16 hours on one engine, 17 on the other.  In 14 years!  But when they hauled it, the nice  ($10,000 EACH) Mercruiser Bravo III outdrives were mere skeletons.  Completely destroyed from the props attached to the shafts emerging from the aluminum case (and no anodes in 14 years).  She already owes more than the boat is worth, and now is facing more than $20k in repairs too.
Expensive lesson in metallurgy

[JD]

Hello , JD here. I just saw your post and wanted to let you know that your first reply to your question is right on. Looks like a short haul is needed and a new cut less bearing. I just had a situation this season after a winter haul out forvbotgom paint.  We launched on the Sassafras River on the northern Chesapeake and found after trying to burp the shaft stuffing bellow that needs to be done after every haul out .... didn't burp water. We have been restoring our 27 for three years and evidently were lucky we did get some water as we stayed in the water for two years.  We found out that the shady log was stuffed with hard debri ..., dark looking sandish material.After taking the forward part of the shaft apart from the transmission we noticed rust contamination . Luckily the shaft is long enough to cut that two inch piece off. and re connect. One of the bolts at the stern was rusted also . Anyway we did replace the Cutless Bering and several bolts in that housing. She is floating fine and plenty of pressure when burped.  My marina owner and his mechanic stated it was the first time they had ever seen this. We think that the debri that entered through the gutless bearing came from years in dirty water along with a few possible grounding related issues in the past along with being on the hard drying the debri.
Hope that helps .. I will soon be adding pics of our on going hole in the water ... we lover though...
Good luck with your project.