After reading up on the available literature, I've seen a general consensus: 316 stainless steel is more corrosion resistant, but weaker - thus, a size larger rigging is indicated.
So I discussed this with Dad, who's been a professor of metallurgy for God knows how many years. Turns out that all the books say 316 has a yield strength similiar to 304 - in fact, depending upon how the metal is worked, 316 could be made stronger than 304, or vice versa. So a blanket statement like "316 is weaker" seems a little, well, ill advised.
Anyhow, the point of all this is that I'm considering replacing the standing rigging. Obviously, economics dictate that one doesn't buy larger rigging than needed. So, if I am fortunate enough to have an expert marine metallurgist out there, I have a few questions:
-first, does 316 really need larger sized rigging:
-second, if it does, could you get away with using normally sized 304 components for the clevis pins etc. - would there be any galvanic potential between the alloys? Dad seems to think not, but he admits he's no expert on corrosion. I guess there's somebody at the University named "Rusty".
As always, thanks for any responses.
huw@post.com
304 vs 316
Moderator: Jim Walsh
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Jack
Re: 304 vs 316
If you read Brion Toss' book and do the load distribution numbers, you will indeed see what so many old salts have said...Cape Dory's were way over built. Yes, 316 wire does have a reduced strength over 304, however even with your current sizes (at least for the CD 27) you still have a safety margin of over 3 to 1 (2.5 is considered more than adequate). Carl Alberg certainly knew what he was doing with the sizes he selected.
Remember that if you have a 5/32" wire (2,900 breaking strength) and tension it 10%, that's 290lbs. If you were to use 3/16" (4,200 breaking strength) at 10% would be 420 lbs. or a 45% increase!....and that is just for the 5/32". At those loads, I'd begin to worry about the strength of the chainplates and the mast step. And, we haven't even begun to talk about the jump from 7/32" to 1/4" for the jib, back and uppers!
Most of the riggers I spoke with advised staying with the current wire size even when switching to 316 s.s.
Remember that if you have a 5/32" wire (2,900 breaking strength) and tension it 10%, that's 290lbs. If you were to use 3/16" (4,200 breaking strength) at 10% would be 420 lbs. or a 45% increase!....and that is just for the 5/32". At those loads, I'd begin to worry about the strength of the chainplates and the mast step. And, we haven't even begun to talk about the jump from 7/32" to 1/4" for the jib, back and uppers!
Most of the riggers I spoke with advised staying with the current wire size even when switching to 316 s.s.