Ground Tackle & Anchor System Sizing TABLES & Swivels

[Steve McGill]

Folks,

This is my current main ground tackle I use for the Chesapeake Bay;

Manson Supreme 35#
1/4" G-4 Hi-Test Chain 30'
5/8" nylon double braid 200'
Suncor Anchor Swivel
5/16" Crosby anchor shackle

My concern is the shackle; it has a WLL of 1,500lbs. I believe this is my weakest link.
Using 1/4" G-4 I am limited to the max pin size of this shackle.

I cannot determine whether this is or should be a point of concern, I could purchase 5/16" chain and upgrade to a 3/8" shackle that would increase the WLL to 2,000lbs.

Are there shackles that are 5/16" with a greater WLL?


Any thoughts to what I have, any suggestions if an upgrade is needed.


Thanks,

Steve

[waterdog]

I can't comment on the working load of your shackle, but don't get too hung up on it.   You design to a particular load, and as soon as you drop it in the water, your system begins to degrade.   The rope chain splice begins to wear.   The chain starts to dissolve.   The rope abrades.   

It's unlikely your system will ever fail because you exceeded the working load of your shackle.   To come to that point, you are in extreme conditions.   Your nylon rode is working over the roller.   If you've been dilligent with chafe protection and it doesn't chew through, internal heat build up in the rode will melt it.     

The real answer is regular inspection because the design specs don't apply after a while.   

I felt real proud of myself.   Made a chain longer by joining two pieces.   The link I used exceeded the strength of chain.   But as I'm hammering away on the rivets, they pound down to a nice shiny finish, and the galvanizing is gone.   So the new link which is stronger than all the others is only that way right now.   Over time, it will become the weak link and it needs to be inspected.   

So if you can get a 2500# shackle great, but I wouldn't worry about it.   Instead, defer your worry until next year and take the time to see if the shackle is corroded, the swivel is in good condition, your splice isn't abraded, your bow roller is good etc.   

[Michael Shaner]

Steve...we have a similar setup (less the swivel w/ 3/8" shackle and 1/2" 8 plait). The Manson wants nothing less than 3/8" "something" shackled to it...makes the puzzle hard to piece together!

I'm consoling myself with the theory of "safe working load" vs. breaking strength...and hoping there is some additional tonnage in between! 

[Stu Jackson]

Steve, you have a very important piece of missing information:  What wind strength did you size your system for?  Other than that, I would do this, altho it's hard to do tables in this forum:


Equipment Component                           Safe Working Load (lbs.)
Manson Supreme 35#                                           insert system reqt

1/4" G-4 Hi-Test Chain 30'                                                             

5/8" nylon double braid 200'   
                                breaking strength=10,500                                         

Suncor Anchor Swivel  if it's stainless it's your weak link, only 750 lbs!  Yikes.  Check the WM catalog and find the exact model to confirm it's load bearing capacity.  The Acco anchor rode swivel is listed at 3900 lbs.

5/16" Crosby anchor shackle  galvanized are rated for 1500 lbs.

You wrote: "Are there shackles that are 5/16" with a greater WLL?"   Not as far as I can see.

So do some back checking first to figure what your system needs to be designed for.  While the shackle may well be the least strong part of your system, the actual question is WHAT STRENGTH DOES YOUR SYSTEM NEED TO BE?  If everything else may be over sized, but the weakest is STILL above your design load, it is NOT a problem.

What wind strength did you use to size the components?

I did a connecting link just as Steve described.  I have on my To Do List: paint connecting link!!!!

[Steve McGill]

Stu,

My Suncor Anchor Swivel has a BL of 8,500lb (http://www.pyacht.com/suncor-anchor-swivel.htm) this is on my anchor and the chain.

I sail at times in winds that are steady at 25-28 knots with 3-5 foot chop/seas. I figured that if I might sail in conditions like that I may also need to anchor in the same.

If I increase my Crosby shackle size to 3/8" (nylon rode/chain) I gain an additional 500lbs of WLL, but then I also need to increase the G-4 chain size to 5/16" to allow for the shackle

What I am unable to figure is the actual forces that are applied on the individual parts.

I am also assuming that the bow cleats or any attachment points on the boat can support this.

As always I understand it's my boat and my decision, but I value the input of the folks here.

Steve

[tonywright]

Steve

I am curious about the shackle. Will you use it between the swivel and the anchor? Is it supposed to deal with side to side loads?  Can you not connect the swivel directly to the anchor? Maybe I am showing my ignorance here, and need to upgrade my ground tackle (my swivel is directly connected)...

BTW the Fortress Anchor site suggests there is a load of 900lb on an average 35ft boat at 30kt windspeed. It doubles to 1800lb at 42kt and again to 3600lb at 60kt.

Thanks

Tony

[Stu Jackson]

1.  My Suncor Anchor Swivel has a BL of 8,500lb (http://www.pyacht.com/suncor-anchor-swivel.htm) this is on my anchor and the chain.

2.  I sail at times in winds that are steady at 25-28 knots with 3-5 foot chop/seas. I figured that if I might sail in conditions like that I may also need to anchor in the same.

3.  If I increase my Crosby shackle size to 3/8" (nylon rode/chain) I gain an additional 500lbs of WLL, but then I also need to increase the G-4 chain size to 5/16" to allow for the shackle.  

4.  What I am unable to figure is the actual forces that are applied on the individual parts.

PLEASE SCROLL DOWN FOR THE SIZING TABLES

This is a great anchor analysis, independent testing:  http://c34.org/bbs/index.php/topic,2705.30.html

1.  That's good, I was going by the 2008 WM catalog and that's all they had there from Suncor.  Great.

2.  Of course, Steve, it's your choice of the "selection" of the wind speed for which you plan to design your system.  You may, or may not, anchor in winds higher than that, say a night time thunderstorm as they get back east.  Given your location, I would reconsider your conditions, based on Ron's input over the years - we don't get those thunderstorms here, least not when and where I choose to anchor.  Your experiences may vary and may not be only the winds you're used to sailing in. Tony's point about wind increases compared to required strength is very well put, and is reflected in the table below.

3.  I think you may have it backwards.  Just because one component is stronger than the other does NOT require the REST of the components to HAVE to be enlarged, unless your point is ONLY about shackles fitting in chain, so, please see #4 below, also, for mixes of shackles to fit chains.

4.  Actual forces:  I have been suggesting that handy reference sources be used, like Calder's Cruising Handbook.  The photos below are the three important tables from that book for sizing anchoring SYSTEMS.  You can wander on down to your local WM store or any handy nautical book chandlery and read the rest of the two pages on how to use the tables, but they're pretty self explanatory.  You've already mentioned "The Gotcha" about this whole exercise:  some chain won't allow a fit of certain sized shackles.  So, it becomes important to plan ahead.  In many cases, windlasses dictate the size and type of chain, with the the rest of the bundle to follow along.

Many have suggested the use of a swivel.  We anchor a lot and have never used or felt we needed one in over 30 years of boating.  We have had chain the length of our boat or more with appropriate rode, have anchored for single nights and many (over four) nights with no issues.  Simple lake anchoring, all the way to opposed wind and current shifts every six hours.  Others have had different experiences.

"What I am unable to figure is the actual forces that are applied on the individual parts."  Those forces are and have to be all the same.  The load on each of the components is exactly the same,  and therefore each component has to equal or exceed the anticipated force based on the boat size and wind strength table below.  Think of the "weakest link in a chain" analogy.

Other than folks with hurricane experience, I have not yet heard of a cleat failing on our boats.

I, too, value the input of the folks on this board.  I also utilize respected reference sources and share them as best I can.

From Steve Dolling's 1500 Mile Report about his anchor system: The importance of using chain and a small amount of rode makes a LOT of sense, and saves all sorts of hassles, compared to the "usual" all chain or chain/rode "argument" ---

The Rocna.  All 20kg of it with 100ft of chain.  The rest of the world can debate all they like.   When I pull into a place like Bodega Bay at midnight and the fog is so thick I can't see the jetty 50 feet away to make an entrance, I drop my hook in the rolling ocean swells with the surf crashing (Foster says it's like staying in a cheap Best Western beside the highway), and I sleep.  And in the morning I have a windlass to pull the beast up and I wouldn't trade it for anything.   (I also wouldn't add more chain - this works perfectly in 25 to 30 feet of water - you let all the chain out and you tie off nylon at the preferred scope and don't bother with snubbers and chain hooks and all that stuff...)

This was our best upgrade.

[Stu Jackson]

Can you not connect the swivel directly to the anchor? ....(my swivel is directly connected)...

Tony -

No it shouldn't be directly connected.  My guess is that you have the jaw end of the swivel right on the anchor.   The reason you shouldn't do that is that the anchor can impart a side load which risks shearing the connector pin at the anchor.  The correct way to install a swivel is:  anchor, a standard anchor shackle with the pin through the anchor shank hole, round end of swivel onto curved end of shackle, jaw end of swivel to anchor chain.

[Ref.: Page 400, Calder's Cruising Handbook]

You might consider moving your swivel to the other end of the chain, where it attaches to the rode, but I do NOT personally know about this, having not used swivels as I noted in the past post.  Heck, if the swivel is there to avoid chain twist, I do not know if it matters what end it's on!   

Only thing, Tony, is to reflect on the first paragraph above.  The failure of a less than $20 piece of metal puts your $50K+++ investment at risk.  If it was my boat, I'd move it or install a shackle as recommended.

[tonywright]

Thanks Stu

I learn more from this board all the time. This will be a priority upgrade.

Tony

[mainesail]

Over the years I have heard of and seen anchor swivels in both stainless (actually mostly stainless) and galvanized fail. Swivels are the weak link despite BL's or breaking loads (which are NOT working loads). You need to consider that the BL is rated on a new un-used swivel when pulled in a straight line load. Because stainless can suffer from crevice corrosion and micro-stress cracking, which then leads to more crevice corrosion, it is generally not the best choice for use in low oxygen water (eg: on the bottom).

In all my years I have yet to see a high quality forged shackle, like those made by Crosby or CM, fail. I'm sure they have but I have not seen nor heard of a true high quality forged and load rated shackle fail (Chinese cast not forged garbage not included).

Over 35+ years I have thousands of anchorings with thousands of tide swings and wind shifts and have never once used a swivel on my anchor set up. I have also never had an issue when not using one that made me wish I had used one.

Also the Crosby shackles are load rated and meet the requirements of Federal Specification RR-C-271D Amendment 1 and are designed to a 6:1 WL/BL standard. This means the BL of the Crosby 5/16" shackles is six times the working load or 9000 pounds! 9000 pounds BL is 500 MORE than your Suncor ( I don't buy that for a minute) swivel.

A couple more points. I would never trust my boat to Loc-Tite below water. If I can't mouse a swivel pin with rigging wire then I don't want it...

I do not personally trust much of what Suncor states and find it VERY odd that they don't publish a WL (working load). I have personally had a failure of a Suncor snap shackle. I had always used Wichard and never once had an ounce of problems but I saved $20.00 and bought a Suncor.. Suncor is IMHO a company who is willing to undercut quality to sell on price. Perhaps they've changed but I won't be going back to them personally.. I would trust a company like Wichard or Crosby but I would be very skeptical of Suncor's claims especially when trusting your boat on it.

The swivel is still your weak link as stated above...

[Steve McGill]

Folks,

Thanks very much for your insight and opinions. It appears that while I still need to evaluate my ground tackle setup I may in fact have been questioning the wrong component/s.

Steve

[Mike and Joanne Stimmler]

I hope you'll consider this related to this post but I've noticed that my anchor rode has turned yellow in the anchor locker. Is this normal or do I need to be concerned?

[Stu Jackson]

Mike, I assume it's standard 3 strand nylon.  Ours did that, too.  I've left it attached to the old Bruce, and use "new" anchor line for our new Rocna.  I used the old anchor line for years even after it yellowed and it was just fine.  There's gotta be a shelf life for it, but it worked and worked for years.  Much of it could be due to yellowing from mud that always gets down into the locker, regardless of how carefully one cleans the line as it comes up from the bottom. That "new" anchor line was stored for years in our aft lazarette and it didn't "age."  Kinda like cheese, I guess.

[Mike and Joanne Stimmler]

Stu, yes it is 3 strand nylon, but it's not that old. I also have a Rocna anchor and I got the line at the same time, about a year and a half ago. Maybe it's just from rain water or even the soap from washing the boat.

[Michael Shaner]

mainesail...outstanding insight...