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  #51  
Old 11-10-2013
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Re: Caternary & Chain...

Quote:
Originally Posted by jrd22 View Post
I think what is missing in this discussion about all chain or chain/rope is that the lighter chain/rope will be a straight line to the anchor, and therefore starting to lift the shank, in much less wind than the all chain. If it takes 160 lbs of force to lift the chain in PS's test it would take a small fraction of that to lift a length of nylon line and 30-40' of chain. So it would seem to follow that the same dynamics on the anchor would happen sooner (much lower wind speeds) than with all chain. Increasing the scope would lower the angle of pull somewhat but would not add weight (catenary) at all compared to all chain. No argument that when the wind speed increases to the point where the chain is bar tight there will be no catenary, but 300' of 3/8" chain is going to keep the pull on the anchor horizontal at much higher wind speeds than an equivalent length of nylon line. So I would assume that the same anchor wouldn't start dragging until the wind maintained enough force to lift the chain.
Yes, but it's a bit like having breaks on your car that work on flat terrain but suddenly fail on hills. The false sense of security outweighs any real benefit.

Quote:
We use a 66 lb Bruce with 300' of 3/8" BBB as our main anchor on a 40' 24,000lb boat.
Nice.

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Brad
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  #52  
Old 11-10-2013
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Re: Caternary & Chain...

"We use a 66lb Bruce with 300' of 3/8" BBB chain."


3/8" BBB chain weighs 1.65 lbs per foot, working load 2750 lbs, coupled with a 66 lb anchor. In lighter breezes there isn't a problem, but when it really blows any catenary disappears and you do or do not drag based on the 66lb anchor alone. If you were to use either a lighter chain or a chain/rope rode with a heavier anchor when it blows you would be relying on a heavier anchor that will not only hold better without the lost catenary but would set better and faster all the time.

G43 chain has a working load of 3900 lbs and weighs just over 1 lb per foot. 300 ft of 5/16" is 198 lbs lighter than 3/8" BBB of the same length. One could use an anchor 50 lbs heavier and still save 148 lbs overall, and have a working load that is 40% larger. Would set faster and give much better holding when that catenary has disappeared due to wind strength. 5/16" G43 is about a dollar less expensive per foot than 3/8" BBB as well for a dollar saving as well based on Jamestown Distributors on line price.

Were one to really get carried away G70 chain of 1/4" size weighs .66 lbs per foot for a chain weight savings of 300 lbs but still has a working load of 3150 lbs, 400 lbs more than the BBB in use currently. Then the size of the anchor can be whatever is desired and there is an even larger total weight savings.

The larger the anchor for a given boat size/displacement the shorter the scope can be if it is necessary in tight places that do not have the swinging room necessary for a 5-1 or larger scope. Of course on a normal basis scope can be 5-1, 7-1 or 10-1 if desired.
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Last edited by mitiempo; 11-10-2013 at 11:15 PM.
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  #53  
Old 11-11-2013
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Re: Caternary & Chain...

Quote:
Originally Posted by Bene505 View Post
Yes, but it's a bit like having breaks on your car that work on flat terrain but suddenly fail on hills. The false sense of security outweighs any real benefit.......
I'm having a hard time seeing it this way. A better analogy would be that all chain is like having superior brakes in 95% of circumstances one drives in.

Put a snubber on chain and use the same scope as rode and you have the other 5% covered too.
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  #54  
Old 11-11-2013
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Re: Caternary & Chain...

Quote:
Originally Posted by mitiempo View Post
"We use a 66lb Bruce with 300' of 3/8" BBB chain."


3/8" BBB chain weighs 1.65 lbs per foot, working load 2750 lbs, coupled with a 66 lb anchor. In lighter breezes there isn't a problem, but when it really blows any catenary disappears and you do or do not drag based on the 66lb anchor alone. If you were to use either a lighter chain or a chain/rope rode with a heavier anchor when it blows you would be relying on a heavier anchor that will not only hold better without the lost catenary but would set better and faster all the time.

G43 chain has a working load of 3900 lbs and weighs just over 1 lb per foot. 300 ft of 5/16" is 198 lbs lighter than 3/8" BBB of the same length. One could use an anchor 50 lbs heavier and still save 148 lbs overall, and have a working load that is 40% larger. Would set faster and give much better holding when that catenary has disappeared due to wind strength. 5/16" G43 is about a dollar less expensive per foot than 3/8" BBB as well for a dollar saving as well based on Jamestown Distributors on line price.

Were one to really get carried away G70 chain of 1/4" size weighs .66 lbs per foot for a chain weight savings of 300 lbs but still has a working load of 3150 lbs, 400 lbs more than the BBB in use currently. Then the size of the anchor can be whatever is desired and there is an even larger total weight savings.

The larger the anchor for a given boat size/displacement the shorter the scope can be if it is necessary in tight places that do not have the swinging room necessary for a 5-1 or larger scope. Of course on a normal basis scope can be 5-1, 7-1 or 10-1 if desired.
What about corrosion resistance? If you lose 1/8" to rust, it would be a much bigger deal on a 1/4" chain than on a 3/8" chain.

Are there data on this for the different chain grades? (honest question, I don't know the answer)
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Re: Caternary & Chain...

Quote:
Originally Posted by MastUndSchotbruch View Post
What about corrosion resistance? If you lose 1/8" to rust, it would be a much bigger deal on a 1/4" chain than on a 3/8" chain.

Are there data on this for the different chain grades? (honest question, I don't know the answer)
I have never seen significant enough rust to feel it was endangering the chain itself. Because of its nature the working limit of chain is much higher than the max load of it. The normal failure mode is for one of the links to stretch slightly (plastic deformation) which is an indicator that the entire length has been over stressed and needs to be replaced.
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  #56  
Old 11-11-2013
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Re: Caternary & Chain...

Here is a link to a great article on chain strength, galvanizing, and re-galvanizing - which is not recommended.

Facts About Anchor Chain Strength and Grades

It is from MorgansCloud
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  #57  
Old 11-11-2013
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Re: Caternary & Chain...

Anyone ever seen a rating from an anchor manufacturer saying what scope their anchor was designed for?
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Old 11-11-2013
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Re: Caternary & Chain...

I think Minne's example of having better brakes 95% of the time is spot on. If you have an oversized anchor and all chain then you have the advantage of the catenary in all situations except when there is enough pull to have all the chain completely straight. In the PS test the values given were only to raise the last link off the bottom, which still gives a horizontal pull on the shank of the anchor and a good deal of catenary. The pull needed to make 300' of chain bar tight would be significantly higher than to just raise the chain off the bottom. Nylon line on the other hand would be a straight line (pulling the anchor upwards) in a light breeze.
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  #59  
Old 11-11-2013
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Re: Caternary & Chain...

The "bad breaks on a car" anology is for chain with little scope. You think it's great until you find out your anchor is getting lifted up and pulled out, in the exact (strong) wind that eliminates your catenary.

Ample scope cures a lot of ills.

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Last edited by Bene505; 11-11-2013 at 08:44 PM.
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  #60  
Old 11-11-2013
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Re: Caternary & Chain...

I don't know about you guys but none of the boats I had (light boats) stayed quiet at anchor on strong wind. Both tended to sail forward on one side than another (and backwards in the middle) using as sail the lazy bag. That diminished the pull on the anchor but made the boats move a lot (forward/Backwards and laterally).

I always used on strong winds two big rubber shock dampeners but I think that the 70 meters of heavy chain play an important role in making this movement a soft rocking one. I don't think that should be soft or agreeable with a textile line instead of chain and I believe that the anchor would be subjected to a lot more violent pulling.
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