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  #11  
Old 11-25-2012
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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.
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  #12  
Old 11-25-2012
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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.
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Old 11-25-2012
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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.
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  #14  
Old 11-26-2012
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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.
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Old 11-27-2012
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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.


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Old 11-27-2012
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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.
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