Josh,
Stress corrosion cracking is caused by chlorides (salt) and high tensile
stress, and while it is always a possibility with 304 and 316 SS,
keeping stress levels low enough with normal safety margins should
minimize it. Not that common in most marine fittings, even in salt water.
Neil Gallagher
Weatherly, 35-1
Glen Cove, NY
On 8/14/2019 10:27 AM, Josh Muckley via CnC-List wrote:
Neil, you mentioned fatigue cracking in aluminum. What about stress
corrosion cracking in SS?
Dan, my thought is that the plates are safe for use of the boat. I
believe it is more likely that the standing rigging will fail before
the chainplates do. I don't know about you but I have plenty of other
boat projects that are more worthy of my money.
Josh Muckley
S/V Sea Hawk
1989 C&C 37+
Solomons, MD
On Wed, Aug 14, 2019, 10:15 AM Neil Gallagher via CnC-List
<cnc-list@cnc-list.com <mailto:cnc-list@cnc-list.com>> wrote:
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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every one is greatly appreciated. If you want to support the list - use PayPal
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_______________________________________________
Thanks everyone for supporting this list with your contributions. Each and
every one is greatly appreciated. If you want to support the list - use PayPal
to send contribution -- https://www.paypal.me/stumurray
