Fashion vs Utility
I suppose that might be true Loren but for a 'quality builder', Ericson sure did some weird things. Encasing a SS chainplate with an obvious crevice corrosion issue is one of them. Why not lay in the glass and THEN install the chainplate..??
But yes... a perfect backing plate. I am replacing my main bulkhead chainplates as I replace the bulkheads themselves... they look fine but I just think it would be a good practice. I will use the old ones as backing plates.
Good observation, but most production builders in the 60's and 70''s did this. Blame
fashion (i.e. the buyers in that era).
Back in earlier decades, all boats would carry their stay loads to external plates bolted thru the hull. Simple and strong.
Then, customers liked the "faster look" of having them go thru the deck even though it added some cost to manufacturing. As production boats were becoming styled after the 70's IOR "look" with wider and wider midsections, there was a great need to move those shroud bases inward to allow decent genoa sheeting angles.
Backstay terminations migrated from the outside of the transom to complete the "modern" look. Remember, all this styling had to please customers attending winter boat shows inside heated buildings -- far from practical stuff like actual sailing.
Soon, only slower-looking cruisers like Westsail (to name only one) kept them external and for them it became like a badge of honor.
Here in PDX, Cascade used the inside-the-hull shroud attachment, altho in their case it was also because it was cheaper than beefing up the cabin sides (original design concept) on the 36 to take the rigging loads. Later when everyone was building wide boats and bringing shroud loads thru the deck, any design without a designed-in bulkhead to tie it to would have to design in extra structure to carry those loads down, like the tie rods in the later EY and Olson designs.
And.... those symmetrical port and starboard bulkheads dictated the interior layout to quite a degree. It takes more engineering and changes in scantlings to bring shroud loads thru an "unsupported" deck to other moldings. But then, you can move interior cabin amenities around much more freely.
Again, the overall "look" of the backstay termination followed right along.
This bit of fashion faded in the 80's.
I do not know, but suspect that buyers started liking the beefier appearance of the external backstay plate, and it was also symmetrical with the external ss forestay plate, too.
Fad and Fashion! I threw away my wide ties (and bell bottom trousers) many decades ago. No more long sideburns, either...
Random observations, from looking at a lot of boats. Deposit one cent, no refunds.