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 TABLESThis is a great anchor analysis, independent testing: http://c34.org/bbs/index.php/topic,2705.30.html1. 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.
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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.