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Warning - chain plates on NZ built production boats


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#11 waikiore

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Posted 23 November 2017 - 10:19 AM

JB is correct, prior to the mid eighties 316 SS was not that common in nz fasteners


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#12 wheels

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Posted 23 November 2017 - 04:46 PM

316 does not mean it is "better" that 304. SST is made to meet a specific requirement for use. 316 offers better protection from Chorides than 304 for example. Which is why 316 is considered better for Salt Water immersion than 304 is. But 316 is also a lot more brittle than 304. This means that 316 can crack due to vibration etc. 304 is a little better and does not work harden as easily. That is why Bolts used to be only available in 304, because cutting threads was really hard work in 316. However, threads are no longer cut. They are rolled into a bolt and hence why you now see 316 just as commonly as 304. Although 316 is often sold at a premium because they can.
Above waterline, 304 can have some big benefits due to being less subject to cracking.
The really big issue the Boating industry has, is the want to have shiny bling for rigging. If only everybody was happy with Galv. If looked after, it can last a life time.
 


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#13 Myjane

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Posted 23 November 2017 - 06:01 PM

I have I think 316 straps either side o foot the chain blocks wich are seen and I autosol polish these once a year when I think of it and no signs of any corrosion ,I hope they are no like this behind
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#14 Chewing Gum

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Posted 23 November 2017 - 07:17 PM

havent heard of any 1020's with that issue,  a 1020 does not have the chain plate bonded to the hull, it is connected via bolts to the main bulkhead which is seperatly bonded to the hull.  only issue i have ever heard of is a couple with massive rig tension needing to go up a size in bolts if the holes slightly ovaled in the wood

 

 

I also think that if you are going to put up a post warning people around certain classes of boats then you should be backing it up with some evidence.  Being in regular contact with 50% of all the 1020's ever built, and knowing the survey results from most of the sales in the last 3-5 years i dont see where you could be getting your information from.

 

​I am also aware of the cause of the rig failures that have occurred in the 1020 class int he last 5 years neither of which relate to chainplates

 

 

It isn't just Kiwi boats

 

Good to hear there have not been many issues with the 1020s. You guys would likely have more idea than me. But all of these boats are quite old now and my source of info is definitely reputable. The reason for my post is just to hopefully save at least one boat owner a lot of hassle and possibly risk. The post from Dtwo is a good example of what to look for ie the staining caused by leaking through the deck. In regard to chainplates bolted to plywood bulkheads - all good unless leaks have rotted the ply or the ply is coming away from the hull. A good look around for staining, rot or even the slightest movement of the chainplates is probably reason to further investigate. Somebody else on this forum is likely more qualified on what to look for.


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PK

#15 Dtwo

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Posted 23 November 2017 - 08:07 PM

See thats actually quite encouraging to see that damage because its not a totally 'hidden' danger.  Thats all quite obvious and would be be showing above or below the deck line upon inspection. And that inspection has prompted the replacement ( Am I right Dtwo?)

It's a known issue on KP44s, built in Taiwan and the quality of the 1977 stainless is shite.  Combine that with a f**kknuckle of an owner who thought that you seal things from the underside, using 5200 liberally coated on everything.  All that did was keep the water from draining away... However, nothing showing anywhere as the chainplates pass through the deck, with all the corrosion happening at deck level, which is about 30mm thick.

 

The bolt that broke was the very first one that I pulled, it made me replace all 30 of them but it was the only really dodgy one, go figure.  I'll ppost a photo of the bolts holding the rudder shoe on in a minute.


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#16 Dtwo

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Posted 23 November 2017 - 08:14 PM

Rudder shoe bolts
 
Now that is "Crevice Corrosion".  Thankfully found after I made it back to NZ...

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#17 Ed

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Posted 23 November 2017 - 08:21 PM

Just had a 1/2" 31600 stainless bolt fail after 10 years of cyclic'ish loading, went just below the nut and looked suspiciously like fatigue that had propogated from a small crack in the thread root. Time to replace the other 15 in the spirit of preventative maintainence 😀
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#18 wild violet

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Posted 23 November 2017 - 09:07 PM

I have a 20 mm bowsprit bolt which came out in two pieces only place on boat with anything important hidden in wood.no chainplates on my old steel boat.
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#19 idlerboat

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Posted 23 November 2017 - 11:10 PM

...another important factor with chain plates is "The leading angle" ,

that is ...That the line of the chainplate is in line with the stay.  As the cyclic loads come on and off , the small amount of deflection in an out of true chainplate can cause it to let go with out any warning. You will find this even more often with Tball fittings. Particularly where they sit in the mast, they often dont allow the wire to run true and it will fail at the point of exit from the swage.


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There is only two substances..stuff and glue...and even glue is made of stuff,,
quote."MD"

#20 lateral

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Posted 24 November 2017 - 07:29 AM

A duplex versus  Austenitic 304/316 comparison here:

 

http://www.steeltank...resentation.pdf

 

As i see it if you stay away from the 0.2% yield zone you reduce the Cl fatigue susceptibility/ work hardening. 

304 & 316 essentially have same yield strength.


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