Sizing Shackle for Chain Rode

[bristol27]

I'm trying to decide which size anchor shackle will fit my planned anchor rode, but I'm having some trouble choosing an anchor shackle with a pin that will fit my anchor rode. Surely someone has solved this question before, so I'm reaching out for some input.

As I understand it, the key for a shackle is that it needs to be stronger than the breaking load of one's rode. Since I plan to use 5/16" proof coil chain, which has a working load limit (WLL) of 1,900 lbs, my shackle should be stronger than or equal to a WLL of 1,900 lbs. However, looking at the shackles here - http://www.hamiltonmarine.com/full.asp?page=149 - all the 5/16" sized shackles have a WLL of less than 1,900 lbs.

It seems that having a shackle of the proper strength, but also fit my 5/16" rode isn't possible without some type of modification of the rode - what am I misunderstanding?

[Rachel]

I'm thinking perhaps a 3/8" shackle will fit? Acco 5/16" Proof coil chain shows a minimum inside width of .50"

For shackles, I like the Crosby brand - either in HT (high-test aka G4) or "regular" (with the red pin) as they are US-made. Here is their website:

http://www.thecrosbygroup.com/

Their 209A model is the HT shackle. The smallest it comes is 3/8", but that has a pin diameter of .44", and a "loop link" diameter of .38" so I'm thinking that should fit into the 5/16" chain, if I'm not mistaken (?). It has a WLL of 2 tons.

On the other hand, even the "regular test" red-pin Crosby shackle in 3/8" has a WLL of 1 ton.

Both of those are on this page of Hamilton Marine's website:
http://store.hamiltonmarine.com/browse. ... 2,565.html

[bristol27]

I see! Now I realize that I should have researched the interior size of the chain. There are also other considerations, as Northstar mentioned, related to the anchor shank, but from my research I believe the anchor I plan to buy (a Rocna 10) will fit this size shackle.

Thanks much for the clarification and I appreciate your answers!

[Case]

Generally speaking, most chains can handle a shackle one size larger. For example, if the chains are 5/16", it will take a 3/8" shackle. 3/8" shackle usually takes a 7/16" shackle and so on. I'm sure there are some odd sized chains out there but accepting a shackle one size larger is the norm.

Mooring chains are a different beast, it can take larger shackles, up to two sizes bigger. Mooring chains are nothing like normal chains, they're much larger for a given diameter. Ignore them for anchoring uses, they're only for mooring uses.

- Case

[Carl-A259]

WLL of 1900lbs (grade 30) seems terribly light for anchor chain, Is that what most are using? just curious. My plan is to use Grade 70 galvinized 5/16". Is this overkill for a 10,000 boat?

[Rachel]

I've always really liked a formula that was in one of the Pardey's earlier books when it comes to selecting chain size and type. They explain how it's windage (vs. weight of boat) that drives the selection and then explain how you can calculate for your own boat and there is a chart showing various wind speeds and strength needed for them. It's very easy on the charts to see the non-linear effect as the wind goes up.

They also discussed chain grades and types, and I vaguely remember some disadvantages to Grade 70 (seemed like G4/High test was the sweet spot in trade-offs) but I can't remember the details now.

I think the discussion was in "The Capable Cruiser."

In the "my own non-physics or analysis-expert" opinions: I'm not convinced that "lighter-but-stronger" chain is an advantage. I also very rarely (ever?) have heard of chain breakage as an anchoring failure (I'm not saying it never happens). It usually seems to be either dragging or some other link in the system failing (chafe, roller, shackle, etc.). On the other hand, it's interesting to me to see how "weak" chain actually is compared to how I think of it (i.e. as this big, burly material).

Rachel