Severe prop pitting

joe4852

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Joe 4852. I think what your asking about would be a shaft tube installed. It would solve a bunch of problems but I looked into doing it and it was and is too big a project at this time.
yes. that's what I was asking. Is it just moving the cutlass inside the existing structure or require a rebuild and stern tube from dripless to cutlass. didn't know if anyone on here attempted it.
 

Providerrrick

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I believe you must glass in a tube from front to back of the keel. Bearings go in the ends of the tube and all must be tried to correct angle and shape. Then because I have a wet keel it would be sealed and water supplied to the whole shaft tube. I think that’s how most downeast boats are done now.
 

Genius

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Actually I see now that I won’t slide the bearing forward or I’ll lose any ability for the flow of water through the bearing. I hope the bearing and housing being just 1 1/2” shorter should be ok? I have the same hull size bearing at the front end of the shaft with a PSS shaft seal.
I think you should be fine. I've heard that when these stern bearings were more common....it was done frequently. If you leave a bit sticking out (3/8?) it may help with change out if you choose to leave the housing in place. No big deal either way IMO.
 

Brooksie

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None of my business but I wouldnt take a sawzall to a good stern bearing housing. I would either 1) get a prop nut zinc. 2) Get a drive saver. The drivesaver will move you back an inch, protect your transmission, and electrically isolate your shaft from the engine and its 12v-. My 2c
 

Brooksie

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I think you should be fine. I've heard that when these stern bearings were more common....it was done frequently. If you leave a bit sticking out (3/8?) it may help with change out if you choose to leave the housing in place. No big deal either way IMO.
Genius, I think he wants to knock it IN (fwd) and cut off the housing to fit a zinc.
 

Genius

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Genius, I think he wants to knock it IN (fwd) and cut off the housing to fit a zinc.
yes. I think I understand what he wants. cutting the after end of the housing off about an inch and a half. I have heard of people doing this. It sill leaves a good area of bearing. But, I do like your idea better.
 

xbskt

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One.
When you check for stray voltage also check polarity to give you intel on if you or the marina is the source of the stray current.
Two.
If you have the space ahead of the rudder I too would add a drivesaver (if you dont already have one) to give you room for a collar zinc. You might not get all the space you need? Imho the propnut zinc is a no brainer here. Do you have a reason not to go that route?
Three.
Looking at it, I would not take your prop beyond the jetty without worrying the whole time I was going to lose a blade or worse put one through my hull.
Four.
I have a 25x25 four blade 2 inch bore I would sell at a fair price if you could use it.
It is Bronze though so may not be suitable for your QSB.

Good luck.
 

Old Mud

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gregs

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I believe Blitzen has the first step. Put in a Galvanic isolator. The other is to check none of your AC wiring neutrals are reversed.
 

Providerrrick

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I’m doing the isolator and going to check for stray current from my boat soon. I can’t do a drive saver without cutting my shaft. Space behind the shaft is only enough to turn the prop past the disconnected rudder. Any further back and I need to drop the rudder which is a job on my boat. I know it’s not ideal but the back of the housing is getting cut.
I moved the boat out of the marina I was in last year to a nicer marina.
I’m still searching for a prop. 25”or 26” diameter. We are thinking of 27 pitch but whatever I buy I will need to cut the front of the hub and can adjust as needed on the size. I believe I need nibral for the QSB. 440 2 1/2:1
 

Blitzen

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I know it is more money but how about a new shaft with a shorter tapper and a new prop with a shorter hub? This way you would gain up at least an inch of space behind the bearing housing.
 

Genius

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FYI, if space and funds are available an isolation transformer is better than a galvanic isolator.
 

Brooksie

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I’m doing the isolator and going to check for stray current from my boat soon. I can’t do a drive saver without cutting my shaft. Space behind the shaft is only enough to turn the prop past the disconnected rudder. Any further back and I need to drop the rudder which is a job on my boat. I know it’s not ideal but the back of the housing is getting cut.
I moved the boat out of the marina I was in last year to a nicer marina.
I’m still searching for a prop. 25”or 26” diameter. We are thinking of 27 pitch but whatever I buy I will need to cut the front of the hub and can adjust as needed on the size. I believe I need nibral for the QSB. 440 2 1/2:1
Your major problem is cavitation. All those spiral lines of pits cutting across the blades is bubble cavitation. You may very well have had stray problems at your other marina and you may also have electrolysis aboard but your main problem looks like cavitation. If you were to run a calc on your setup you may be well in cavitation range. I see the two hollows molded into your keel but I also see all the square corners and the transducer.
Again I would not cut the cutlass housing the Drivesaver and the zinc prop nut will solve your zinc problem and will solve an electrolisis problem by isolating your shaft from the engine ground. If you want to remove the prop, just remove the Drivesaver, not the rudder, 20 min extra work. You need to remove it to do an alignment anyway.
 
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Providerrrick

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Here’s a quick update. Waiting until I put the new prop on and try it out. I ended up fairing out the area at the back of the keel and cutting the stern bearing housing back just enough to fit a collar zinc. This should address the water quality a bit and the protection of the running gear from electrolysis.

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