Cruisers Forum
 


Reply
  This discussion is proudly sponsored by:
Please support our sponsors and let them know you heard about their products on Cruisers Forums. Advertise Here
 
Thread Tools Search this Thread Rate Thread Display Modes
Old 01-01-2011, 09:40   #1
Registered User
 
sww914's Avatar

Join Date: May 2009
Location: Punta De Mita
Boat: Vagabond 39 Hull # 1
Posts: 1,842
Pitted Prop Shaft Repair ?

Yes, I know I should just replace it. I'm trying to save some money where it's possible, my financial outlook isn't good now but in a couple of years it will be better, I'm just tired of waiting to go cruising and trying to get started sooner rather than later.
My prop shaft is pitted in the area inside of the shaft log. It's not in a sealing area or where either of the bearings mount. It's between the shaft packing and the cutlass bearing. The largest pits are about the same mass as 3-4 bb's, most about like 1-2 bb's and there are a couple dozen pits spread out along 12" of the 1 1/2" shaft. Can these be repaired? Should I ignore them?

On the Porsche racecars that I build, we can routinely run 300hp through a 1" shaft without any problems as long as the driver doesn't think he's a burnout king. 1 1/2" seems plenty strong enough for 50-60 hp even if it's strength is a little compromised.
Attached Thumbnails
Click image for larger version

Name:	shaft 001 (Large).jpg
Views:	1017
Size:	47.3 KB
ID:	22424   Click image for larger version

Name:	shaft 002 (Large).jpg
Views:	826
Size:	45.7 KB
ID:	22425  

sww914 is offline   Reply With Quote
Old 01-01-2011, 09:48   #2
Registered User
 
RainDog's Avatar

Join Date: Jun 2009
Location: Pensacola, FL
Posts: 1,261
Afraid I have no answer for your question, but as an aside.... Have your priced replacing it? My friend just replaced his and I was shocked how cheap the part was ($160). Might be cheaper than you think.
RainDog is offline   Reply With Quote
Old 02-01-2011, 08:03   #3
Registered User
 
DeepFrz's Avatar

Cruisers Forum Supporter

Join Date: Mar 2006
Location: Winnipeg
Boat: None at this time
Posts: 8,462
The problem is you can't tell how deep the corrosion goes into the shaft. I looked at that second picture and knew right away that if it was my boat I would replace the shaft.
DeepFrz is offline   Reply With Quote
Old 02-01-2011, 08:24   #4
Moderator Emeritus
 
David M's Avatar

Cruisers Forum Supporter

Join Date: Sep 2007
Location: Eastern Tennessee
Boat: Research vessel for a university, retired now.
Posts: 10,406
The reason this has occurred is the lack of oxygen to the stainless steel. I know it sounds counter-intuitive, but stainless steel needs oxygen to help prevent it from going active.

One solution would be to get a drippless shaft seal with a nipple that allows pressurized sea water from the engines cooling system to be injected into the area between the cutlass bearing and the shaft seal.

I realize this is the last thing you want to hear because of the cost but it is something you could add in the future when replacing your corroded propeller shaft.
__________________
David

Life begins where land ends.
David M is offline   Reply With Quote
Old 02-01-2011, 08:27   #5
Hull Diver
 
fstbttms's Avatar

Cruisers Forum Supporter

Join Date: Oct 2006
Location: Under a boat, in a marina, in the San Francisco Bay
Posts: 5,427
Quote:
Originally Posted by sww914 View Post
On the Porsche racecars that I build, we can routinely run 300hp through a 1" shaft without any problems as long as the driver doesn't think he's a burnout king. 1 1/2" seems plenty strong enough for 50-60 hp even if it's strength is a little compromised.
Yes, but when the driveshaft on a Porsche fails, you aren't left in the middle of an ocean with no motor.
fstbttms is offline   Reply With Quote
Old 02-01-2011, 08:32   #6
CF Adviser
 
Bash's Avatar

Join Date: Dec 2008
Location: sausalito
Boat: 14 meter sloop
Posts: 7,260
Quote:
Originally Posted by sww914 View Post
Yes, I know I should just replace it.
You won't got any argument from me. Yes, you should just replace it.
__________________
cruising is entirely about showing up--in boat shoes.
Bash is offline   Reply With Quote
Old 02-01-2011, 08:37   #7
Moderator Emeritus
 
David M's Avatar

Cruisers Forum Supporter

Join Date: Sep 2007
Location: Eastern Tennessee
Boat: Research vessel for a university, retired now.
Posts: 10,406
The limiting factor for a propeller shaft is torque and not horsepower. These are two very different things.

The way that it works is you can run a propeller shaft at 6000 RPM with little torque and produce a given horsepower. Or you can slow down the RPM, increase the torque and have the same horsepower produced by the propeller...essentially by increasing the pitch and/or diameter of the propeller.

Or in other words, in order to produce the same horsepower, when a shaft turns slower, the torque must be increased. When you increase the torque, the diameter of the shaft must be increased.
__________________
David

Life begins where land ends.
David M is offline   Reply With Quote
Old 02-01-2011, 09:43   #8
Registered User
 
svHyLyte's Avatar

Join Date: Mar 2006
Location: Tampa Bay area, USA
Boat: Beneteau First 42
Posts: 3,961
Images: 25
Quote:
Originally Posted by sww914 View Post
Yes, I know I should just replace it. I'm trying to save some money where it's possible, my financial outlook isn't good now but in a couple of years it will be better, I'm just tired of waiting to go cruising and trying to get started sooner rather than later.
My prop shaft is pitted in the area inside of the shaft log. It's not in a sealing area or where either of the bearings mount. It's between the shaft packing and the cutlass bearing. The largest pits are about the same mass as 3-4 bb's, most about like 1-2 bb's and there are a couple dozen pits spread out along 12" of the 1 1/2" shaft. Can these be repaired? Should I ignore them?

On the Porsche racecars that I build, we can routinely run 300hp through a 1" shaft without any problems as long as the driver doesn't think he's a burnout king. 1 1/2" seems plenty strong enough for 50-60 hp even if it's strength is a little compromised.
We discovered similar damage to our prop-shaft when we did our bi-annual haulout in January '09. I discovered that a repair--grinding out the pits, building up the shaft with weldment and then re-machining the shaft to size at a local machine shop--would have cost about as much as a replacement shaft with no warranty.

FWIW...
__________________
"It is not so much for its beauty that the Sea makes a claim upon men's hearts, as for that subtle something, that quality of air, that emanation from the waves, that so wonderfully renews a weary spirit."
svHyLyte is offline   Reply With Quote
Old 02-01-2011, 09:54   #9
Moderator Emeritus
 
David M's Avatar

Cruisers Forum Supporter

Join Date: Sep 2007
Location: Eastern Tennessee
Boat: Research vessel for a university, retired now.
Posts: 10,406
Welding on stainless may weaken the shaft. All you might do is to make it look pretty again with no gain in strength...possibly a loss in strength. I'm no expert at welding stainless but I do know that welding metal has the potential of weakening the metal or making it more brittle. You will want to consult with an expert on this.
__________________
David

Life begins where land ends.
David M is offline   Reply With Quote
Old 02-01-2011, 11:38   #10
֍֎֍֎֍֎֍֎֍֎

Join Date: Apr 2006
Posts: 15,136
I'd be afraid that pits of that size are a sign of unseen "crevice corrosion" which leads to sudden and complete failure in stainless parts. It will be way cheaper to replace that shaft now, than to call a tow and deal with all the consequences of a failure away from the dock.

Personally, I'd go with the new shaft. The old one can be tested, but between the cost of tests and repairs...cheaper faster easier better to just replace it. Shop around while the need isn't urgent.

I'd disagree about a dripless shaft seal, that's another expense and simply using a GoreTex dripless packing material should do very nicely with a new clean shaft.
hellosailor is offline   Reply With Quote
Old 02-01-2011, 11:44   #11
Moderator Emeritus
 
David M's Avatar

Cruisers Forum Supporter

Join Date: Sep 2007
Location: Eastern Tennessee
Boat: Research vessel for a university, retired now.
Posts: 10,406
I have had nothing but good luck in over twenty years I have been using drippless shaft seals.
__________________
David

Life begins where land ends.
David M is offline   Reply With Quote
Old 02-01-2011, 12:33   #12
Registered User

Join Date: Sep 2009
Location: On the Gorge waterway in the heart of Victoria, British Columbia.
Boat: Explorer 44 by Stan Huntingford. Building in progress.
Posts: 30
So how about moving the location of the shaft seal forward onto a new and clear section of shaft. Put an extender tube on the shaft log to move the shaft seal forward.

Cheers

BB
Bruce Bevan is offline   Reply With Quote
Old 02-01-2011, 12:44   #13
Registered User
 
sailvayu's Avatar

Join Date: Mar 2006
Location: Fort Myers FL
Boat: Irwin 40
Posts: 878
No question replace it. As for shaft seals and injecting water yeah that would help but only when the engine is running. That is a very small time compared with the time the boat is in the water without the engine running, so it really does no good for this problem. Check for galvanic current flow just to be on the safe side.
__________________
Capt. Wayne Canning, AMS
www.projectboat.info
https://sailvayu.com/
sailvayu is offline   Reply With Quote
Old 02-01-2011, 13:11   #14
֍֎֍֎֍֎֍֎֍֎

Join Date: Apr 2006
Posts: 15,136
Quote:
Originally Posted by David M View Post
I have had nothing but good luck in over twenty years I have been using drippless shaft seals.
Luck should have nothing to do with it.<G>

I have nothing about patent seals, but note that some folks have had them fail in ways a plain log simply can't. And that buying and installing them is of course an expense.

When the dripless seals were first invented and marketed--great idea. IIRC the dripless packing (GoreTex string or teflon putty) didn't come on the market until quite some time later, but it is available now, and much cheaper than a patent seal.
hellosailor is offline   Reply With Quote
Old 02-01-2011, 13:19   #15
Registered User
 
Cavalier's Avatar

Join Date: Dec 2010
Location: Houston, TX
Boat: Beneteau 461 47'
Posts: 927
Images: 1
Quote:
Originally Posted by fstbttms

Yes, but when the driveshaft on a Porsche fails, you aren't left in the middle of an ocean with no motor.
Unless, of course, you're driving along a Californian cliff top road when the draftshaft fails on your twitchy rear-ended Porsche - then you may well find yourself in the ocean with no motor ;-)
__________________
"By day the hot sun fermented us; and we were dizzied by the beating wind. At night we were stained by dew, and shamed into pettiness by the innumerable silences of stars."
Cavalier is offline   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Prop Shaft ksmith Construction, Maintenance & Refit 8 03-08-2009 11:02
Prop Shaft Rattle seanseamour Propellers & Drive Systems 7 02-08-2009 19:27
prop shaft down angle of 12° (+) vacendak Propellers & Drive Systems 5 11-02-2009 01:18
Bent prop shaft, repair or replace Thistle Construction, Maintenance & Refit 6 30-05-2008 05:19
Prop shaft alloy restlessnic Propellers & Drive Systems 4 07-03-2008 06:09

Advertise Here


All times are GMT -7. The time now is 03:18.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2024, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.