Corroded Shackle - SailNet Community
Reply
 
LinkBack Thread Tools
post #1 of 19 Old 01-04-2009 Thread Starter
Member
 
Join Date: Oct 2007
Location: Vancouver, Canada
Posts: 88
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 8
 
Corroded Shackle

We just replaced this 5/8" shackle that was connecting our bob-stay to the boat, right at the waterline. That pin was responsible for supporting such useful items as: the mast. I can't believe how corroded it turned out to be, it's pretty much hollow inside. There was very little indication of a problem from the outside - when swimming this summer we noticed a little pitting, so put it on the to-do list. Makes you really think about checking your rig.


Pacific Seacraft Mariah 31
dhornsey is offline  
Quote Quick Reply Share with Facebook
Sponsored Links
Advertisement
 
post #2 of 19 Old 01-04-2009
Senior Member
 
Join Date: Apr 2008
Location: Melbourne, Florida
Posts: 418
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 8
 
WOW! Good catch. Maybe some of that counterfeit stainless? At any rate, looks like you dodged a real bullet there d.
fullkeel7 is offline  
Quote Quick Reply Share with Facebook
post #3 of 19 Old 01-04-2009
Senior Member
 
Join Date: Mar 2008
Posts: 888
Thanks: 0
Thanked 1 Time in 1 Post
Rep Power: 8
 
NOW you know what 'crevice corrosion' looks like. Stainless steel, in the presense of water, and not exposed to the air, plus mechanical galling (stainless against stainless is extremely bad) gets you really accelerated corrosion. This is why stainless is not used below the water line. It is also why stainless keel bolts with just a tiny leak around the keel can literally be gone before you know it!
GaryHLucas is offline  
Quote Quick Reply Share with Facebook
post #4 of 19 Old 01-04-2009
Detachable member
 
wchevron's Avatar
 
Join Date: Oct 2007
Location: rhode island
Posts: 376
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 8
 
gary
i thought the whole reason to use stainless was it corroded less than steel. also, why would you get galling with two like metals.

wchevron
s/v Time Flies
'78 C-30
wchevron is offline  
Quote Quick Reply Share with Facebook
post #5 of 19 Old 01-04-2009
Senior Member
 
Join Date: Apr 2008
Location: Melbourne, Florida
Posts: 418
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 8
 
From what I've read, even high quality stainless (ie 316) needs oxygen to be effective. I suspect in dhornsey's example, a lower grade stainless was used. Be interesting to know if those peices are slightly magnetic.

Also that shackle pin is under a fair amount of tension and movement (although slight) through wave action on the bob stay and sail pressures through the forestay. Pin could have developed a slight crack and the water did the rest.
fullkeel7 is offline  
Quote Quick Reply Share with Facebook
post #6 of 19 Old 01-04-2009
Owner, Green Bay Packers
 
Join Date: Sep 2006
Location: SW Michigan
Posts: 10,318
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 12
       
I'm going to hazard a guess that that is not crevice corrosion. I'd think it much more likely to be due to galvanic action with the pin being the less noble metal.

“Scientists are people who build the Brooklyn Bridge and then buy it.”
Wm. F. Buckley, Jr.
sailaway21 is offline  
Quote Quick Reply Share with Facebook
post #7 of 19 Old 01-04-2009
Senior Member
 
Join Date: Jun 2004
Location: West Michigan
Posts: 515
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 12
 
Galling is pretty similar to welding, and is often called cold welding. Two like metals will often gall because they have the same physical properties. It's a lot like rubbing two candles together, rub them together and they'll stick, take them apart and you have bits of each stuck in the other.
Aluminum to aluminum, steel to steel etc will all gall.
Iron to Iron, and bronze to bronze is normally fine though. (iron has a high ratio of carbon which acts as a lube so it doesn't gall under ordinary conditions)
Dissimilar metals won't gall, but then you introduce galvanic corrosion.

Galling is not a problem for parts securely fastened together, only when they are free to move against each other.

Ken.

Meant to quote wchevron
merc2dogs is offline  
Quote Quick Reply Share with Facebook
post #8 of 19 Old 01-04-2009 Thread Starter
Member
 
Join Date: Oct 2007
Location: Vancouver, Canada
Posts: 88
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 8
 
There was definitely a lot of movement between the shackle pin and it's mounting plate, as we fasten our anchor line to that shackle at times. I have no idea how old the shackle is, but the plate that is is fastened to shows no signs of corrosion whatsoever. Also, being right at the waterline, they are both constantly dipped in salt water. Seems like the perfect environment for corrosion, whatever type it is. I'll certainly check these things more often.

Pacific Seacraft Mariah 31
dhornsey is offline  
Quote Quick Reply Share with Facebook
post #9 of 19 Old 01-05-2009
midlife crisis member
 
AllThumbs's Avatar
 
Join Date: Jul 2008
Posts: 975
Thanks: 0
Thanked 10 Times in 8 Posts
Rep Power: 7
 
Quote:
Galling is not a problem for parts securely fastened together, only when they are free to move against each other.
This is true but you need one more ingredient to assure galling: Pressure

Actually this phenomenon is put to good use in industry, where parts can be permanently welded by just rubbing them together under extreme pressure.

Eric

I sail.
AllThumbs is offline  
Quote Quick Reply Share with Facebook
post #10 of 19 Old 01-05-2009
Senior Member
 
tommays's Avatar
 
Join Date: Sep 2008
Posts: 4,296
Thanks: 1
Thanked 30 Times in 30 Posts
Rep Power: 7
 
Without knowing if it is 3 years old or 30 it is a tough call, At 30 it was just left unchecked to long at 3 there is something wrong

1970 Cal 29 Sea Fever

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

1981 J24 Tangent 2930
Tommays
Northport NY


If a dirty bottom slows you down what do you think it does to your boat
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
tommays is offline  
Quote Quick Reply Share with Facebook
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the SailNet Community forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
Please note: After entering 3 characters a list of Usernames already in use will appear and the list will disappear once a valid Username is entered.


User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in









Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



Similar Threads
Thread Thread Starter Forum Replies Last Post
Replacing Corroded Mast Step pearson301 Gear & Maintenance 29 01-11-2015 08:19 PM
corroded stanchions northstarjim Gear & Maintenance 5 08-29-2007 08:51 PM
Opinion on Wichard Quick Release Shackle? labatt Gear & Maintenance 3 07-16-2007 12:25 PM
corroded wiring HoffaLives Gear & Maintenance 5 05-05-2007 02:16 PM
Corroded lifeline stanchions BallastBoy Gear & Maintenance 6 02-28-2002 10:23 AM

Posting Rules  
You may post new threads
You may 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 On
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome