LET’S TALK CHAINPLATES (again)

[buzzerk]

hello all . . .

Hunter 36 1980 model

Has any Hunter 36 owner of this age experienced and care to relate their chainplate failure?

My stem fitting is currently being rebuilt due to stress cracking below the toggle pin hole. (I believe some blame lies with previous / present operator error, over tightened headstay/backstay) And I plan to sleeve (ss) the bearing holes in the hull and deck as these are wallered oversize. As well as replace the aft ‘u’ bolts. No catastrophic failures . . . yet. The other six chainplates seem to be ok on a quick visual ck, but who knows at this age??

This of course goes to service life of the base material, 304 / 316ss. 35 years seems to be the time.

One poster (J. Cherubini II) stated that 304 was the material of choice due to the embrittlement factor of 316. And I am also thinking about the associated problems of welding the additional bearing washers for the toggle pin above the deck.

But, the bigger problem for stainless seems to be the danger of oxygen starvation when sealing the thru deck hole and crevice corrosion stress cracking.

This brings me (IMHO) to silicon bronze and chucking ss as the replacement material for new chainplates.

So, the question is 1) How to stop the leaks at the thru deck holes for the chainplates if I use ss? 2) Is a simple visual (dye penetrant / 4x loupe) chainplate inspection adequate, or is it time for x-ray? 3) Or is it simply time, and address the leak problem?

Thanks for the input . . .

Tom
s/v Driftwood
Oakland Estuary

 

[rufus1138]

i would think the bronze would lack sufficient tensile strength. its quite soft really. if you're worried about the mounting holes in the fg then fill them and re-drill with the new stem fitting, also what is excessive headstay tension and what is simple chain plate aging.

 

[buzzerk]

rufus . . . SILICON bronze (C65500) . . . think jib tracks . . . turnbuckles . . . those thingies they hang rudders from . . . etc

filling holes is NOT how we aircraft mechanics fix on airplanes . . . and yes that is exactly what the metal shop suggested . . . and I respectfully declined . . . and aircraft bolts (and their associated smooth grip lengths), while far superior to the threaded junk we have available for use, is also far too expensive . . . ss sleeves will not allow the threads to contact the fg . . .

Not to mention the chore of finding a "make me smaller" pill so I could get to the inside of the bow close enuf to do the required work . . . just getting the washers stick and place on the inside of the vertical fasteners is challenge enuf . . .

excessive tension . . . see what happened in the one 'Conner' America's Cup challenge . . . broke his boat in two . . . (if my memory serves me) . . .

there are other posts concerning standing rigging pre-loading . . . usually 10-20% working load . . .

that's my question "chainplate aging"

Tom
s/v Driftwood
Oakland Estuary

 

[woodster]

the dead eyes on the schooner America are made of a high tensile strength bronze alloy and they hold just fine.......

 

[rufus1138]

you dont have to preach to me about aircraft standards i have my a+p as well, i was talking about filling the fg holes with a proper repair and re-drilling them using the stem fitting as a template. use bronze if you like, id rather stick with ss since thats been industry standard for chainplates for a long time now, http://www.makeitfrom.com/compare-materials/?A=Phosphor-Bronze&B=Stainless-Steel ...ill just leave this here.