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Old 29-06-2013, 19:57   #1
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Anchors and Chain

Catenary & Scope In Anchor Rode: Anchor Systems For Small Boats

Appreciating that the whole anchor scenario has been done to death, I would never the less like to offer the above link for your consideration.
This is not a question relating to the use of chain or rope around coral, or the longevity of one system versus the other, just the author's argument regarding the holding power of rope rodes.
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Old 29-06-2013, 22:10   #2
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Way to mess with my anchor lifestyle smugness.,

I'm all chain big chain heavy chain because well forget math it works. It really does.
Here is why. If I can throw a small one pound stone 30 yards a heavy 6 lb stone 10 yards then the 6 lb stone is more effected by gravity. Forget Cantinery think gravity. This weight effects set at the time I set. Plus it's really heavy and it sinks harder. I know this because its harder to lift. Never mind that. It relays on a snubber that has 2100 lbs breaking strength minus the knot loss makes it around 1300 lbs. I'm worried that my shackle that will fail at 4000 lbs isn't strong enough. Bahhhh with your math.
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Old 29-06-2013, 23:12   #3
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Re: Anchors and chain

Cliffnotes: an anchor company advises you to buy a heavier and thereby more expensive anchor.
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Old 30-06-2013, 14:52   #4
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Re: Anchors and chain

Yes, I take the point about research from an anchor manufacturer.
However, what I was hoping for was a critique of the math and science behind his rationale, not gut feeling. Every advance in every field has been the result of someone questioning whether there 'is a better way'. For me, doing something a certain way because we always do it that way just doesn't cut it.
I will experiment.
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Old 30-06-2013, 15:09   #5
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On a slightly different subject, has anyone had experience using chain links to attach extra lengths of chain together?
Is this a reliable way to go? We have some rusted chain in the middle of a 200 ft length and wonder of we can simple cut this section out and add new.
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Old 30-06-2013, 15:31   #6
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Re: Anchors and chain

Yes, they do work. Do NOT buy "quick links" but make sure you get chain links. The ones you hammer the little "buttons" down. I put one on to link two shorter lengths of chain, and it's been working fine for 10 years. I check it every time I lower and raise our anchor.
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Old 30-06-2013, 15:44   #7
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Re: Anchors and chain

Quote:
Originally Posted by Stu Jackson View Post
Yes, they do work. Do NOT buy "quick links" but make sure you get chain links. The ones you hammer the little "buttons" down. I put one on to link two shorter lengths of chain, and it's been working fine for 10 years. I check it every time I lower and raise our anchor.
If there were a hurricane coming, would you trust that link?
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Old 30-06-2013, 16:10   #8
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Re: Anchors and chain

I have chain and I have nylon.
I anchor in deep places and in shallow places.
I anchor in sand and mud and I anchor among rock and coral.
I anchor in clam winds and strong winds.
I anchor in a short fetch or a long fetch.
I use one of my anchors or one of my other anchors or maybe two.

I adapt and so can you!
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Old 30-06-2013, 16:29   #9
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Re: Anchors and chain

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Originally Posted by davecalvert View Post
On a slightly different subject, has anyone had experience using chain links to attach extra lengths of chain together?................
The best answer for this may depend upon your windlass. I use two Crosby shackles to connect a new shot of chain and this just causes a brief "hiccup" across my Simpson Lawrence manual windlass gypsy. I like the Crosby shackles, but the answer depends on your windlass.
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Old 30-06-2013, 17:26   #10
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Re: Anchors and chain

If you want it to pass through the windlass, try the Crosby S-249 Twin Clevis Link (hat tip, Nick, s/v Jedi). The WLL is on par with the same sized G70 chain.
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Old 30-06-2013, 17:49   #11
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Re: Anchors and chain

Does anyone know of a US source for 10mm DIN chain. I have a Goiot windlass and don't want to change the wildcat.
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Old 30-06-2013, 17:51   #12
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Re: Anchors and chain

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If you want it to pass through the windlass, try the Crosby S-249 Twin Clevis Link (hat tip, Nick, s/v Jedi). The WLL is on par with the same sized G70 chain.
But it is just covered in thin red paint.
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Old 30-06-2013, 17:54   #13
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Re: Anchors and chain

Commenting upon the original query raised by the OP.

I see a number of flaws in the thesis.

It is difficult to argue with the concept that given the finite amount and size of chain we can carry then at say. 40 knots, there is little or no catenary left. Even if we could carry more than the finite amount the catenary would be effectively lost at say 45 knots. Consequently the advantage of the catenary is over stated (and a lighter chain would not be much different to a heavier chain) - you might enjoy an extra margin of 'safety' of 5-10 knots for say a 10mm chain over a 8mm chain.

However given the difference being small the argument that we should use smaller chain and bigger anchors is very questionable. If one accepts the 5-10knots difference then anchor makers should be recommended bigger in the first place. I see this as a flaw in the thesis. Smith seems to say catenary is not all its cracked up to be, going smaller will not make much difference (to the effect of catenary) but you should buy a bigger anchor - even though the difference in the 'safety margin' might only be 10 knots. Being honest they should be recommending bigger anchors in the first place.

Smith also says bigger (anchors) will give a 'massive' increase in performance, this is also questionable. Based on the thesis that holding capacity increases linearly with surface area and that load, or whatever you want to call it, (from wind) increases by the square of wind speed then a doubling of holding capacity will result in a very small safety margin of increased wind speed. To me the idea of the bigger anchor is a questionable, for different reasons, as the idea of the smaller chain.

I do not question the underlying thesis that catenary is overrated, I do question the idea that an anchor maker does not have an ulterior motive for suggesting you buy a bigger anchor. Of course the thesis as proposed is based on one anchor design and might have much merit, for that design due to some design quirk or other. However I do not see other anchor makers, Spade, Fortress, Anchor Right et all offering any support at all for the arguments proposed by Smith.

I might suggest that no-one is going to sit out 40 knot winds without snubbers and without introducing them to equation you simply have a marketing argument on behalf of an anchor maker.

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Old 30-06-2013, 18:02   #14
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Re: Anchors and chain

Quote:
Originally Posted by Chrisc View Post
Yes, I take the point about research from an anchor manufacturer.
However, what I was hoping for was a critique of the math and science behind his rationale, not gut feeling. Every advance in every field has been the result of someone questioning whether there 'is a better way'. For me, doing something a certain way because we always do it that way just doesn't cut it.
I will experiment.
Unfortunately, one has to take everything Mr. Smith says with a grain of salt. Lots of good information, but you have to sift out the self serving prevarications to get benefit from his advice.

Most of this is borrowed (like his anchor design was borrowed from Bugel) from Alain Fraysee's meticulous calculation on rodes and the forces they are subjected to.

Forces

I think the lesson is that a mixed rode is best because it combines the increased catenary of chain in lower wind conditions with the reduction in shock forces on all chain rodes. The same effect is accomplished with an appropriate snubber system that I frankly find a whole lot easier to handle than a mixed rode. There is a great thread on this topic you can find ihere: http://www.cruisersforum.com/forums/...er-104325.html

The basic issue is that a snub line stretches. If it stretches 5 feet in gusts, then the shock force placed on the anchor and gear is approximately 1/5 what it would be without the snub line. For this reason, most cruisers seem to go with something around 30', octoplait or 3 strand that gives around 10' of stretch. As you can see in the above mentioned thread, some add a backup snub line of greater diameter that is sized to begin to take the load off the primary snub line once it begins to reach its maximum stretch. These snubbers are easy to attach, quiet things down while still allowing the carrying of all chain that is certainly the best choice in most cases for lots of reasons - assuming you can handle the bow weight.
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Old 30-06-2013, 18:29   #15
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Re: Anchors and chain

Thank you - excellent, reasoned replies.
My interest stems from the fact that I mainly anchor in a depth of 3 - 8m, mainly on sand or mud,(not much coral in NZ) and having now only a 30' yacht with not a great deal of reserve buoyancy, am keen to save weight where I can, especially forward. Currently I have 20m of 8mm chain and then a vast amount of 8 plait nylon, and a similar setup on my secondary anchor.
3 strand nylon is generally a pain in the bum to handle but I find 8plait almost as easy to stow as chain, so I guess I'll stick with what I have?
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