Dan,
Grade 316 stainless is about two to three times as strong as aluminum,
it varies a lot depending on what grade Al you're using. (Some numbers:
utlimate tensile strength of 316 SS is about 84,000 psi, aluminum
6061-T6, a common marine alloy, is 42,000 psi) SS is also less prone to
cracking under fatigue loading.
IMHO those chainplates aren't all that bad, the holes are not elongated,
just a little rough. It'd be nice to see the top of the holes where the
load is transferred, but what's visible is decent. There's no
significant wastage in thickness, appears to be mostly the surface
coating that has worn off. If you're really concerned you can have them
dye penetrant tested for cracks, could be done in place.
Of course free advice is worth what you pay for it....
Neil Gallagher
Weatherly, 35-1
Glen Cove, NY
On 8/14/2019 9:42 AM, Dan via CnC-List wrote:
Fortunately our yard doesn't get involved with stepping and unstepping
masts so it's 100% my discretion.
I know a guy who does stainless. I was thinking about getting him to
check out the plates and quote me on new ones made to spec, except
instead of 1/2" thickness throughout, I would ask for the below deck
portion to be 1/4" or 3/8" thickness. I'm under the impression that
stainless is much stronger and can be thinner to achieve the
equivalent strength to the aluminum plates. I'm not an engineer, but
I'd sail with that setup.
If these aluminum plates are fine as is for another 5 years or so I
can put this job off. I've seen much worse corrosion.
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