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Go Back   SailNet Community > General Interest > General Discussion (sailing related) > "The chainplate will buff out and probably be okay"
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Thread: "The chainplate will buff out and probably be okay" Reply to Thread
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Topic Review (Newest First)
11-27-2012 09:16 AM
chucklesR
Re: "The chainplate will buff out and probably be okay"

"I didn't see the need for stainless"

Translated - the next owner will have a little project in a year or two.
11-27-2012 12:24 AM
MedSailor
Re: "The chainplate will buff out and probably be okay"

Quote:
Originally Posted by xymotic View Post
Bob Perry personally talked me out of looking at Tayana 37's largely due to chainplate issues.
PFFFFFFFTHHH!!! Don't listen to Bob Perry! What, you think he knows something just because he designed them!?! If he's so smart then where is HIS youtube video? Go with the guy on the youtube video, he sounds like he knows what he's talking about. All you need is some of this to buff it out.


MedSailor
11-26-2012 12:24 AM
xymotic
Re: "The chainplate will buff out and probably be okay"

Bob Perry personally talked me out of looking at Tayana 37's largely due to chainplate issues.
11-25-2012 11:45 PM
Stumble
Re: "The chainplate will buff out and probably be okay"

Cheerev,

External chainplates aren't that much better than internal. While its true that the side that is exposed is usually fine, the side against the hull is as prone to corrosion as an internal, except that because it is almost always wet, corrosion can be even worse.

Certainly they have different problems, but they do still have them.
11-25-2012 11:16 PM
cherev
Re: "The chainplate will buff out and probably be okay"

The exterior chain-plates of the Morgan OI is the best approach. Stainless steel needs oxygen and sunlight to remain sound.

Never allow dissimilar metals to touch, or at least never in any place difficult/impossible to inspect. Even stainless components in contact should all have same number:


The hairline crack story was apposite.
11-25-2012 10:05 PM
RichH
Re: "The chainplate will buff out and probably be okay"

What your looking at is the Bob Perry design that even by scantling history has withstood the test of time ... probably more of these 'knees' have circumnavigated (Valiant, Tayana, Tashiba, Baba, Valiant) than any other design combined.
This design is quite robust, and comes with a inbuilt safety factor of approximately 4:1, well above the normal 3:1 found on most 'blue water boats'.

The only real flaws of this design is the internal wood which carries the moisture that since ~1975 (now 35 years after the fact) is now for the past few years has been showing severe vulnerability. The other vulnerability is that this arrangement is (or can be) a 'friction connection' and needs routine maintenance torquing ... if properly torqued, those bolts will NOT be in shear but rather only supply the 'clamping (compressive) force' which enables the joint/join surfaces to carry all the loads through stress transmitted 'normal' (a vector component in friction) loads; induced friction between the mating surfaces is what makes this 'joint' work .... and without a lot of 'stress risers' as is found in MOST other 'flat plate' designs, quite impressive for a then ~26 year old 'kid' designer if in fact that is what Bob Perry intended.

Such a repair is quit easy and straight forward for those not timid with composite FRG work. To make this assembly 'work' and remove all the vulnerabilities of moisture intrusion ... simply reconstruct without wood, and change the studs into removable shoulder bolts, and be sure to use a torque wrench when assembling. Certainly MUCH better than using an external chainplate design where the loading on those 'bolts/studs' are 'sequential' due to the elasticity of the stainless and where the bolts are vulnerable to maximum shear loads... sequentially, and resultant 'bearing saddle stress' (a stress riser) during the 'elastic stretch' under max. load of such a long chainplate. The 'secret' of this design is that the studs are welded to a strap which is encased (drilled into) in wood behind the fiberglass web; replace the wood with non-permeable material and weld the nuts to the 'strap' so the bolts can be removed and routinely inspected and 99% of the vulnerabilities of this design are gone ... permanently.


If that chainplate through deck and/or the screwed down teak decks were extremely well maintained, you'd not be seeing such 'grief' .... and the only 'maintenance' would be to routinely change out those chainplates at approx. 1 million load cycles (about 1+ circumnavigation) for fatigue considerations.
11-25-2012 08:09 PM
SloopJonB
Re: "The chainplate will buff out and probably be okay"

Quote:
Originally Posted by mjf55 View Post
Monotone voice aside, it was very interesting. The question I have is that repair he made, circular plywood plugs in the knee, steel back plates sufficient? Should the plugs have been joined together? Fiberglass laid over the whole knee repair? Aluminum vs steel backing plates? Or am I just overbuilding again ? Thoughts?

Sent from my DROID X2 using Tapatalk 2
The mild steel backer was LAME - spend the extra $2 and get stainless strap from a scrapyard. Mild steel will ALWAYS rot on a boat - did you catch how it was in the head and the trim cover wasn't going back on?

Throughbolting them through the hull is plenty strong, especially with all that plywood bedded in epoxy as well.

That original installation is one of the worst designs I have ever seen - I mean really, cobbled up T-Bolts set in as studs? I guess glassed in chains might be a little worse but it would be debatable.

I dearly hope the Maestro didn't spec that horrible setup.

IMHO, the only way to have chainplates set up is to have them fully exposed and bolted through a knee or bulkhead.

P.S. The guy doing the video obviously isn't a SailNetter or he would NEVER have said, in all seriousness "That'll buff out".
11-25-2012 06:30 PM
Stumble
Re: "The chainplate will buff out and probably be okay"

Quote:
Originally Posted by mjf55 View Post
Monotone voice aside, it was very interesting. The question I have is that repair he made, circular plywood plugs in the knee, steel back plates sufficient? Should the plugs have been joined together? Fiberglass laid over the whole knee repair? Aluminum vs steel backing plates? Or am I just overbuilding again ? Thoughts?

Sent from my DROID X2 using Tapatalk 2
Steel+aluminium+stainless+water is pretty much the definition of an electrolysis problem. Wood anywhere near chainplates is equally a bad idea. They get so heavily loaded even fully encapsulated wood will eventually have the sheathing breached, leading to rot.

Add in that chainplates are often out of sight, or difficult to get to, and there is nothing about this repair that is anything other than a problem waiting to happen.
11-25-2012 05:05 PM
SloopJonB
Re: "The chainplate will buff out and probably be okay"

I posted a while back about my chainplate experience - I took the headstay fitting off to polish - it looked fine but wasn't OCD shiny, as I require.

After buffing it with a 1/2 horse buffing machine I noticed what looked like a faint hairline scratch across the front surface of the tang portion below the welded portion. You had to catch the light across it just right to even see it. I buffed it some more but it was still there. I held it at both ends and pulled and it slowly bent like taffy until it snapped across that "scratch".

I immediately pulled every chain in the boat and made up new ones which I had electropolished.

Crevice corrosion can be VERY subtle.
11-25-2012 04:37 PM
mjf55 Monotone voice aside, it was very interesting. The question I have is that repair he made, circular plywood plugs in the knee, steel back plates sufficient? Should the plugs have been joined together? Fiberglass laid over the whole knee repair? Aluminum vs steel backing plates? Or am I just overbuilding again ? Thoughts?

Sent from my DROID X2 using Tapatalk 2
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