New Chainplate

[PaulM]

All,
I need to have a new chainplate fabricated to replace one that broke. I pulled the other side to use as a template. I don’t like the way it was constructed. The construction is three piece. The long tang (~3.5’) is bolted to the bulkhead in the cabin. The tang then goes thru the deck and is welded to the bottom of the “beauty plate” that is screwed to the top of the deck. The third piece that accepts both cap shroud and lower turnbuckles is welded to the top of the “beauty plate” at 90˚ to the long tang. Is having the chainplate integrity dependent on two welds asking for trouble? Am I being overly cautious? If not, does any one have any ideas on how to correct.

Thanks
PaulM
Pearson 303

[Douglas]

Oh , you are wise to ask that question about welded chainplate fittings.

Although I am not a rigger, except for my own rig, I have read a number of books about marine DIY surveying, and found it mentioned a number of times, that it is not an approved practice to hang anything structural on a welded fitting.

I have seen it done, even on my former ss bowsprit cranze iron .

It was difficult for me to find out why a ss welded fitting could not be depended on, structurally. From what I could find out, is that when you weld on ss , the molten puddle, boils off some chrome and nickle, thus you don't have a marine grade 18-8 alloy any more , all along that weld .

Some welders said to me, where you can not avoid using a welded ss structural fitting, you can use an "enrichening" filler rod, thus replacing the chrome and nickle that would normally be lost or vaporized to the air in the welding puddle.

I have had this enrichening rod used on my ss welded swim ladder , and I expected to see the normal rusting occur on and around the weld, but the corrosion evidenced by rust, has not appeared yet after 3 years, hurray !

[Brian Duff]

I think you do have cause for concern with a chainplate such as that.
With the uppers and lowers on that same deckplatetang,set at athwartships , it can and will see-saw on the fore and aft chainplate welded below it. The 'captive' deck plate helps resist fatigue from working, but the welded design is to be avoided when possible. This chainplate arrangement is done on many production boats,with either a rod or chainplate or cable, in answer to the same interior decorator needs as your 303, and it does fail more easily than a straight piece of flat bar would.

Maybe you could carry that fore and aft flatbar chainplate up through the deck and weld a deck plate around it. Perhaps just adding some gussets to the existing set-up would be enough to increase resistance to working and add more weld area, for strength

"Nothin' too strong ever broke." -Maine proverb (thanks Brion)


Have fun with your boat