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Boomkin Tangs Revisited

  • May 05, 2013 3:40 PM
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    Reply # 1286109 on 1069610
    Anonymous
    An internal view of crevice corrosion.  
    http://i1121.photobucket.com/albums/l518/svsundowner/chainplate-broken.jpg


    This is the cross section of a chainplate that I replaced showing the insidious nature of this type of corrosion.  Only a hairline crack showed on the backside of the plate but upon removal it snapped in two at that point.  You can see how deep it had gotten.
    Last modified: May 06, 2013 5:54 PM | Anonymous member (Administrator)
  • May 05, 2013 7:28 PM
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    Reply # 1286219 on 1069610
    Deleted user
    FYI I had plates waterjetted from titanium.  Not too expensive.  You can buy surplus titanium and have it jetted for almost the same cost as 316SS (if you are willing to clean them up after jetting) because SS needs to be polished and passivated.  Titanium is not as finicky.  I am slowly replacing all critical SS with titanium.  Why?  I, too, took down a structural p[iece of SS (the inside bulwark straps on a W43 which are bolted to the chain plates on the inside of the cabin) and they crumbled in my hands.  Long story short  the chainplates needed inspection as the stb side had never been off the boat since new as far as I could tell and with those straps completey failed I feared a similar fate for the chainplates.  Well I made the titanium plates before removing the old chainplates and lo and behold the old chainplates which were electroplished 316SS 3/8" were pristine. 

    If anyone is interested in fabbing titanium it isn't that difficult but you do need real tools not Home Depot stuff as the stuff is really tough.

    Cheers
  • May 06, 2013 3:54 AM
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    Reply # 1286349 on 1069610
    Anonymous member
    Thanks for sharing, Jay, Tate and Edward. Those are some scary photos! If you can send me larger originals, I'll see that they get into the "Things that Fail" section of Bud's website.

    I have a good friend, Paul,  in St. Petersburg, FL who is currently refitting his CSY 37 for a circumnavigation that is due to commence in about a year. He found crevice corrosion on his chainplates when they were removed for inspection cleaning. Paul is incredibly articulate when it comes to such things. (Some might accuse him of being "anal-retentive", but I know he's just incredibly "detail-oriented".) So, when he discovered the corrosion, he located some titanium bar stock and about 60 titanium bolts to remake all of his chainplates. He swears by the stuff and I'm sure he's right. Though the cost would normally have been rather prohibitive, by finding the right stuff at the right price, he did rather well. Of course, he couldn't get anyone to touch the machining, so he also bought a bigger drill press and a hydraulic bender to do it himself. If one disregards his time investment (which we all know is "free"), he actually came out quite well.

    Paul is rather busy, but perhaps I can convince him to spend some time to share his experience. I envy his diligence and talents in the shop!

    Jack
  • May 06, 2013 1:21 PM
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    Reply # 1286823 on 1069610
    Deleted user
    I am not sure where he got affordable Titanium? but if you can get it, it would be a nice addition to the boat.

    See the below paper on using it within the marine environment.
    http://www.ticotitanium.com/wp-content/uploads/2009/11/paper02170.pdf

    This is just a FYI on the material.
  • May 06, 2013 4:15 PM
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    Reply # 1286989 on 1069610
    Anonymous
    I agree that titanium is a far superior material for chainplates.  Before we replaced ours I did a lot of research and just about everything except the price is superior to SS.  In the end we were getting killed by the death of a thousand pokes.  Sure Ti was better than SS and it was only X dollars more expensive.  And the Ti bolts/washers/nuts were only X dollars more expensive (since you don't want to mix SS and Ti).  And on and on with all the upgrades.  

    In the end, we figured, SS should last 10 - 15 years, is slightly cheaper, and we could order from Bud with no hassle of a fabricator or shopping Ti bar stock, or worry about how to put a bend in it.  So we went with SS.  

    All that said...  SS is a devilish material that always hides its flaws until its ready to fail in a glorious explosion.  So keep your eyes on it! 
  • May 07, 2013 3:29 PM
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    Reply # 1287832 on 1069610
    Deleted user
    FYI I was just letting people know that titanium is doable.  Not as daunting as it may seem.  The key is waterjetting to tight tolerances and then of course carbide and diamond tipped cutting tools.  Bending is tricky though as the stuff is springy as all get out!!!
  • July 09, 2013 7:19 AM
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    Reply # 1336509 on 1069610
    Deleted user
    A little something else about titanium rigging.

    Sorry,
    Steve
  • July 09, 2013 3:39 PM
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    Reply # 1336914 on 1069610
    Deleted user
    Great read Steve:

    From the very very fuzzy pic it look like embrittlement.  They also looked thin ??  not sure how they bent the titanium. This could have had some effect as well as what alloy they used.

    In any case here is a place to read more about the corrosion issues for this material.

    http://www.azom.com/article.aspx?ArticleID=1239

    Not sure which alloy they were using but it sounds like something was very very wrong.

    Norm
    Last modified: July 09, 2013 3:40 PM | Deleted user
  • July 10, 2013 7:31 AM
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    Reply # 1337364 on 1069610
    Anonymous member

    Since I am in the quoting process for my entire standing rigging, I gave Colligo Marine a chance to defend themselves to me.  Here is the conversation:

    Tyler: "John,
     
    I do not want to be a prickly being, but am I at risk for something like this?
     
    http://www.oddasea.com/archives/142-A-bit-about-the-dismasting....html
     
    He directly names Colligo Marine part failure.  I'm not pointing fingers, I'm just inquiring.  I think we are going with the Cheeky tangs, and shouldn't have this problem.  Please discuss to the extent you are legally allowed.
     
    Thanks,"

    John: "Hi Tyler,  thanks for forwarding this.  We had the tangs in question analyzed professionally and it was determined that this was a secondary failure, Probably the spreader broke or buckled first and then overloaded the brackets in a very fast loading scenario.  The strain rate sensitivity of titanium could produce a failure in this area if the loading was fast.   We have pull tested several pairs of the brackets and the failure mode is not even in that location, it is around the holes as you would imagine.  It is highly improbable that the primary failure was in this location. 


    We have many pairs of these brackets out there on other, larger boats for over 5 years with no failures, even on rotating masts.

    We have not heard of any secondary boat  with an issue.  Not sure where that is coming from but might be he is not happy with our assessment, not sure.  Daniel contact me about this issue last summer and, would not send me the brackets, saying they were being analyzed.  I did not hear from him until last December and then he finally sent me the brackets, so we could analyze them.  Not timely to say the least.  We did offer to sell him a rig at wholesale but I think he is now going with a stayless rig.


    Since you are using the cheeky tangs your risk of any issue is pretty low."

    I work in fatigue failure analysis, and after review of the poorly focused picture I have to side with Colligo Marine.  That fracture does not display fatigue characteristics typically observed.  It appears to have been a single overloaded failure behavior and fracture surface, most probable as a secondary failure to something else that was never recovered in the dismasting.  We may never fully understand the details because the rig was lost. 

    I understand there is no such thing as a free lunch, but jumping to conclusions without further review of all the evidence is dangerous.

    T.
  • July 10, 2013 9:41 AM
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    Reply # 1337466 on 1069610
    Deleted user
    Tyler:

    From the photo (it is TRUE we can not make any real comments! it is to poor a view to make any real informed statement, to this end, my above comment was a GUESS and not a statement.) There should have been a metallurgic review of the break on the item, they did not talk about this in your post nor did the author of the article.

    But I am going to have to call them on the stress rate issue, as this part is attached to a ss stay ( which was not reported to have parted).

    I hope you have some idea on how far a stay can stretch before failure (then you under stand that we are talking about longer time lines). like 50 to 100 milliseconds on load rate even with a broken spreader / slipped mast etc. etc. ) that stay is like a spring it really stretches and stretches and stretches allot+++++  we are talking almost inches which = time to load the part.

    Not impact type stuff at 10 to the -6 or faster which can have an effect.

    Here is a good read on some stuff the military did with regard to this subject and Ti. http://www.dtic.mil/dtic/tr/fulltext/u2/a379805.pdf    Page 16 is a good go to for the idea. The whole paper is more directed at higher temps and surface exposure.

    So before the above response I would have guessed ???? ( not sure)  but after the response above,  I believe I would do allot more research before going with plates like the ones in the article (this is my opinion) but as always please please do the research yourself).

    Norm

    Please note: I make no comment on (if this was primary or secondary.) I just want to point out ref. info. for the reader to review.  

    Hope this is helpful in some way.

    Lastly it would be nice to know if the author was using a ssb or ham on the boat.

    Last modified: July 10, 2013 10:08 AM | Deleted user