Of chain and shackles

Dean Abramson · Post by **Dean Abramson** » Apr 13th, '10, 10:53

They say that a chain is only as good as "the weakest link." What they ought to say is "the shackle."

I am changing my anchor rode shackles.

It bugs me that the SWL of shackles is way lower than the chain, even if you go the one size up. Your basic weak link. A 5/16 shackle has a SWL of 1500 lbs., but my 5/16 HT chain is rated at 2850. Is this huge difference because there is no such thing as a high-test shackle? (If I follow convention and use a 3/8 shackle, it's 2000 lbs, still 850 less than the chain.) I looked at stainless shackles, but the ratings apparently are identical to their galvanized counterparts.

I am not sure how much wind it takes on a CD31 with lots of scope to generates 1500 lbs of pull. Then you have the waves' impact.

Am I missing something? Is the only answer to change your shackles every couple of years, in hopes that they are always at their best? And that is all you can do? Larger shackles than one-size-up will not fit thru the chain.

Dean

Dean

Numbah134 · Post by **Numbah134** » Apr 13th, '10, 11:19

Try page 1410, 1412 of McMaster-Carr catalog at www.mcmaster.com

They have a 3/8 hot-dipped alloy shackle rated at 4000 lbs. Also powder-coat (don't know how that would hold up) 9/32 at 4300 and 3/8 at 8000.

The stainless options are mostly less robust. But read on, I poked a bit further.

Items specified "for lifting" tend to be built to a higher standard than those not specified as such.

Page 1414 does have a twisted stainless 5/16 with a 2975 lb WLL, not for lifting - might be the ticket for you? The 3/8 is 4960. I would use stainless safety wire to ensure the pin not backing out.

bgephart · Post by **bgephart** » Apr 13th, '10, 11:50

My CD-25 is anchored in a tidal creek Bahama style, with one anchor upstream on chain attached to a mooring ball, and a second anchor downstream on 1/2 inch nylon with a short chain at the anchor. The 3/8 inch galvanized shackle purchased from WM attaching the chain to the mooring ball failed. The point of failure was the threads of the shackle pin - they had just disappeared. This shackle was less than 2 years old and I had not seen any problem when I inspected it a few months previous. Happily my anchors still held, but it took a few days to find and retrieve the mooring ball. Lesson learned - pay extra attention to the shackle pin threads.

Cathy Monaghan · Post by **Cathy Monaghan** » Apr 13th, '10, 12:03

Hi Dean,

Make sure your shackles are forged not cast. There is a BIG difference.

Cathy
CD32 Realization, #3
Rahway, NJ
Raritan Bay

Klem · Post by **Klem** » Apr 13th, '10, 13:02

Crosby makes shackles with a slightly higher SWL. I use a 3/8" shackle rated at 2T SWL which exceeds the chain that it is attached to. If your anchor can take it, the ideal thing to do is to get chain with an enlarged end link (installed by the chain manufacturer) and then use a larger load rated shackle.

Cathy Monaghan · Post by **Cathy Monaghan** » Apr 13th, '10, 16:31

Klem wrote:Crosby makes shackles with a slightly higher SWL. I use a 3/8" shackle rated at 2T SWL which exceeds the chain that it is attached to. If your anchor can take it, the ideal thing to do is to get chain with an enlarged end link (installed by the chain manufacturer) and then use a larger load rated shackle.

Dean,

Crosby makes both carbon screw pin shackles and alloy screw pin shackles. They are both forged and hot-dipped galvanized. The alloy screw pin shackles are more heavy-duty than the carbon ones. But the alloy screw pin shackles are pretty well matched with the G3 chain even though the WLL is less. [Minimum Ultimate Strength for G3 chain should be 4 times the working load limit and it is proof tested at 2 times the working load limit.]

Click on the links below for more info on the Crosby shackles:

Carbon Screw Pin Shackles: http://www.thecrosbygroup.com/html/en-US/pdf/pgs/65.pdf
[NOTE: Maximum Proof Load is 2.0 times the Working Load Limit. Minimum Ultimate Strength is 6 times the Working Load Limit. For Working Load Limit reduction due to side loading applications, see page 74.]

Alloy Screw Pin Shackles: http://www.thecrosbygroup.com/html/en-US/pdf/pgs/66.pdf
[* Maximum Proof Load is 2 times the Working Load Limit (metric tons) and 2.2 times the Working Load Limit (short tons). Minimum Ultimate Strength is 4.5 times the Working Load Limit for metric tonnes, and 5 times the Working Load Limit for short tons. For Working Load Limit reduction due to side loading applications, see page 74.]

Hope this helps you pick the right shackles. By the way, Defender carries Crosby shackles. Their forged alloy screw pin shackles have a red pin.

You may want to look at Seachoice shackles too.

Cathy

Carl Thunberg · Post by **Carl Thunberg** » Apr 14th, '10, 06:35

Dean,

Not to detract from anything the others have said, the difference is due to the failure mode of the materials involved. A shackle pin is in double shear, which means that the load is transferred from the shackle to the chain by placing the shackle pin in shear. It's double shear because the same pin is subjected to shear in two planes. Chain on the other hand is governed by its tensile strength, which is a lot greater than its shear strength.

Bob Ohler · Post by **Bob Ohler** » Apr 14th, '10, 07:55

This may be nerdy for some, but this is an excellent thread!
Cathy, thanks for pointing out cast vs. forged. Rule of thumb, (but not always the case) a forged piece is 3 times stronger than a cast piece of identical design.

The suggestion of McMaster Carr is also a great idea.

All hardware stores have gone almost exclusively to cast products made in China. It is good to know that Crosby is still around.

My father had very large two trucks and rigging equipment. He taught me years ago the value of Crosby alloy.

Thanks!
Bob O.

Dean Abramson · Post by **Dean Abramson** » Apr 14th, '10, 08:49

After reading all of the excellent advice here, perusing the linked websites, and searching out older threads re ground tackle, I decided to order some Crosby shackles. A 3/8 from the nylon (eye with thimble) to the chain, and 7/16 from the chain to the anchor.

One major factor was this info from Cathy and Crosby:
Minimum Ultimate Strength is 5 times the Working Load Limit for short tons. That, and discussion of actual typical loads, gave me a different outlook on all of this.

Also, I am getting rid of the rusty Chinese swivel which is now a part of my primary rode! My research leads me to believe that for my use, swivels are not necessary, and possibly problematic. (Not only that, but Rich Abato says so.)

I was thrilled to find out that my thimbled eye and a 3/8 shackle will just pass thru my new chain-stopper.

Thanks to everyone for the help.

Dean

Bob Ohler · Post by **Bob Ohler** » Apr 15th, '10, 07:58

Have we determined yet... are the ones from McMaster Carr Crosby shackles? (I looked at the McMaster catalog online and I did not see the brand mentioned.) If not, does anyone know where to go to purchase the Crosby shackles previously discussed in this thread?

Bob O.

Dean Abramson · Post by **Dean Abramson** » Apr 15th, '10, 08:05

I ordered my Crosby shackles from Defender. It was/is not clear whether they are the carbon or the alloy ones. They are not here yet.

I chose not to pursue the McMaster Carr ones, and know nothing about them other than the description on the web.

Dean

Bob Ohler · Post by **Bob Ohler** » Apr 15th, '10, 08:08

Dean, be sure to let us know what you get from Defender. Crosby? Carbon pin? Alloy, etc?

Thanks,

Bob O.

Dean Abramson · Post by **Dean Abramson** » Apr 15th, '10, 08:18

I should have mentioned that I asked McMaster if those Shackles came in 5/16 and 7/16, and they don't. Only 1/8" increments. If they had had 5/16, I would have gone for one (for nylon-to-chain), because it would fit more easily thru my chain stopper. A 3/8 will pass thru, but it is tight.

Dean

Duncan Maio · Post by **Duncan Maio** » Apr 15th, '10, 08:26

We get our rigging stuff from Peak Trading:

Peak Trading Corp.
43 Basin Road Unit #1
West Hurley, NY 12491

Telephone Number: Toll Free 1-800-952-7325 or (845) 338-1325
Fax (845) 338-1372

Cathy Monaghan · Post by **Cathy Monaghan** » Apr 15th, '10, 11:34

Dean Abramson wrote:I ordered my Crosby shackles from Defender. It was/is not clear whether they are the carbon or the alloy ones. They are not here yet.

I chose not to pursue the McMaster Carr ones, and know nothing about them other than the description on the web.

Dean

If you ordered them from Defender, they are the carbon screw pin shackles for use with BBB and proof coil chain. Hamilton Marine carries both the carbon and the alloy Crosby shackles.

Crosby isn't the only U.S. manufacturer of chain and shackles. In addition to Crosby there's Columbus McKinnon.

I know that both Defender and Hamilton Marine carry the Crosby shackles. Jamestown Distributors has the Columbus McKinnon shackles. They're not the only ones. You can go to either the Crosby or the Columbus McKinnon web sites, find the shackle that you want, then use GOOGLE to search on the part number.

Cathy

The Cape Dory Board

Of chain and shackles

Of chain and shackles

Can get better...

My shackle failed

Forged not cast...

Mechanics of Materials

Great Thread!

Decision

Source for Crosby Products?

Dean... let us know...