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From: Larry N. Brown (no email)
Date: Sat Dec 01 2007 - 17:15:47 EST
I've spent a great deal of bandwith asking about swivels and anchor shackles.
I've seen a great deal more used on replies, speculation and suggestions. This
morning I received two emails offline that answered my questions to
perfection. See if I can condense it a bit.
>From the preponderance of emails, I've decided I'll do without the swivels.
I'll use instead, two anchor shackles, the pin of one going through the anchor
shank hole and the pin of the other going through the last link of the anchor
chain. One listee who emailed me, used a fancy dancy SS swivel on the shank
of his aluminum Spade He bent the shank and he's soured on swivels and
aluminum anchors.
Now let's talk about anchors, shackles, chain and boats. I'll give you some
numbers for 3/8" HT galvanized chain and associated hardware but you can
easily get the numbers for smaller or larger stuff. Listed working strength of
HT chain is rated at 1/3 of it's breaking strength. 3/8" HT is listed as 5400#
working load. That means that its breaking strength is around 16,200. The
alloy shackle breaking strength is 4 to 5 times the rated working strength.
The CM galvanized alloy 7/16" pin anchor shackle is rated at 2 5/8 ton or
5250#. At 4 -5 to 1, that gives us 20,800 to 26,250 breaking strength. The
shackles will not be the failure point and most likely neither will the chain
if it is in good condition.
So. If the anchor is well set and the chain and shackle appear to be in good
condition, the most likely failure point is where the rode comes aboard the
boat or the point at which it is attached to the boat. From which we can fork
off into Samson posts and chain snubbers and wind loading.
Regards,
Larry and Teri
M/V Cigano, 47' Prairie Sundeck Cruiser
Lying: Covington, LA
N 30 26.7
W 90 07.1
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