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Chain plate life span

  • May 28, 2014 3:05 PM
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    Message # 1558254
    Anonymous member
    I have been told by an engineer that the life span of the chain plates, or any cyclic stressed metal, is 25 years. Sosiego is 40 years old and she has been re-rigged twice but retains her original chain plates. Does any one have an opinion ? How do change the chain plate at the water line on the end of the bob stay?
  • May 28, 2014 4:50 PM
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    Reply # 1558275 on 1558254
    Deleted user
    Joseph Any Chance you can tell us where your engineer graduated from?
    Some notes:
     a. the tension on the plate could be from 0 to say 9360# but should be cycled between 800# and 2K (NON IMPACT cycling)
    b. the cross section is 1/4" x 2" less the holes = .375" sq
    c. The stress riser for the square holes is 1.3+/-
    d.) the top end is attached to a 9/32" dia wire = .06212" sq = 1/6 that of the chain plate.
    e. the stress is about 0.1 to 0.2 on the wire

    Some thoughts.
    1. if you extrapulate out the chart on page 68 of http://www.nrc.gov/reading-rm/doc-collections/nuregs/contract /cr6787/cr6787.pdf you may find it takes about 8100days of constant sailing to reach the end of the life on the wire 8100/365 = 22 year of constant sailing assuming a 7 sec period. for the plate it would be at least 6 times that # and most likely 10X.
    2. the issues with the chain plates and rig is the corrosion, not the cycle life. Corrosion can reduce the life by ? as much as 20+ times on the ocean = 22*6/20= 6.6 years if they cracked and rusting it could be even less.
    3. inspection is the only way to see if the life is 132 Years or 6.6 years.
    4. if you are mostly rust free and NO cracks then look forward to another 132-40+/- years of service +/- Lastly: NO one (Including me can without close inspection tell you how much life you have in the chain plates or your wires) Hope this helps you (Think about it for your self, as I hope you are the smartest person you know)

    opps: your other question (cut it out from the inside of the chain locker)

    Oh back in 2003 I had my bow tang x=rayed (looked good but the bow tang is the one item I do worry about )  not the best design for inspection.
    Last modified: May 28, 2014 5:18 PM | Deleted user
  • May 28, 2014 5:38 PM
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    Reply # 1558296 on 1558254
    Anonymous member (Administrator)

    Joe:

    Here is a link to the Items that break album with images of several failures.  

    As Norm says - it's the corrosion ... look at the below as this is a classic example from Pygmalion - then further down for the result after removal.  Note the crack looks small but acutally is 1/2 the width+.

    There are a couple of things to worry about - the holes for the carriage bolts are square - the corners makes a great place to start cracks - Bud has offered a version with round holes and fasteners that with an allen wrench will tighten nicely.

    With the chain plate flush against the hull and if the area is oxygen starved and a little moist then the corrosion can/will get started. 

    Short of removing each chain plate - you can polish and check closely for any sign of a cracks especially near the bolt holes.

    Now here is a way to really lighten your wallet... Way below is an image of bronze chain plates on "Constanza" which I'm told is a W32...

     

     

    Constanza - Bob Kingston - several years ago.
  • May 28, 2014 8:27 PM
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    Reply # 1558333 on 1558254
    Anonymous
    The previous owners of our W32 also had some reservations about that bobstay chainplate which resulted in one of the oddities of our boat.  They installed a second chainplate above the internal bobstay plate.  Its bolted to the hull.  This means we actually have two bobstays on our boat, one right in front of the other. 

    As a side note, if the chainplates are 40 years old I would change them.  Period.  When we pulled our chainplates, they were a mess but you couldn't see it from the outside.  When in doubt pull them.  On the W32 they're very easy to pull and change.  Bud offers a very fair price for new ones.
  • May 29, 2014 8:36 AM
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    Reply # 1558541 on 1558254
    Deleted user
    I have chainplates (used in my garage) from a refit if anyone wants them.  They look good.  A simple dye test would reveal any problems.  I'll sell the lot of ten for 200 plus shipping.  Not sure how old maybe 15years?