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  #31  
Old 11-09-2013
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Re: Caternary & Chain...

Quote:
Originally Posted by smurphny View Post
... it is MUCH easier to "feel" the anchor set when using rope/chain. With all chain it is almost impossible to feel the anchor grabbing and work it in by hand because the chain wants to go straight down and create so much caternary that there is little indication on the boat end as to what the anchor is actually doing....
This is a good point that is seldom stated. When I switched from line to chain I felt I had gone blind. I could no longer "see" the bottom material through the line. At the same time I had switched from a Fortress to a "new" anchor and understood why folks where so wild about it; it was less necessary to feel it in. In shallow water and tight anchorages (common for cats) we like to "feel" the initial set. In deeper water this difference is probably noticeable.

No obvious solution, since most of us chose chain for abrasion resistance and ease on the windlass.
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  #32  
Old 11-10-2013
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Re: Caternary & Chain...

Quote:
Originally Posted by mitiempo View Post
Marty, I read that article as well. Basic conclusion was that when catenary is needed the most, as in a strong blow, it didn't exist as whatever rode is used it is bar tight.
That was the other thing in the article, was in 60 mph plus winds, an all chain was pulling straight from teh bow of the boat to the anchor, and as such, the angle of pull was greater than a 10-1 with partial chain and rope rode. So the angle the anchor was getting pulled on was less, hence better. If one did chain at 10-1, it might be a bit better than rope, but reality, either would be pulled straight! The rope having some give/stretch was the better option.

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  #33  
Old 11-10-2013
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Re: Caternary & Chain...

Quote:
Originally Posted by blt2ski View Post
That was the other thing in the article, was in 60 mph plus winds, an all chain was pulling straight from teh bow of the boat to the anchor, and as such, the angle of pull was greater than a 10-1 with partial chain and rope rode. So the angle the anchor was getting pulled on was less, hence better. If one did chain at 10-1, it might be a bit better than rope, but reality, either would be pulled straight! The rope having some give/stretch was the better option.

Marty
But the results of the PS testing show that it takes considerably less than 60 mph to straighten the chain and lift the last link off the bottom at 5-1 - 15 knots. With that proven even at 10-1 the last link should be off the bottom well before 60. And who really has swinging room for 10-1 anyway?
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  #34  
Old 11-10-2013
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Re: Caternary & Chain...

What am I suppose to do with this new knowledge of how little pull it takes to lift the chain?

I was feeling safe and happy before, am I suppose to be scared to anchor now?
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  #35  
Old 11-10-2013
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Re: Caternary & Chain...

Quote:
Originally Posted by Don0190 View Post
What am I suppose to do with this new knowledge of how little pull it takes to lift the chain?

I was feeling safe and happy before, am I suppose to be scared to anchor now?
Just use more scope when it gets snotty. 5:1 can be adequate under many conditions, with many anchors, but some really need a shallower shank angle to continue to hold...

I think this data only serves to confirm what Peter Smith has been saying for years, put the weight in the anchor, not the chain....

The less scope you have the easier it is to lift the rode and minimize or nearly eliminate caternary...... The less scope you have the easier it is to shock load deck fittings. The less scope you have means the more elastic your snubber needs to be...
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  #36  
Old 11-10-2013
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Re: Caternary & Chain...

IMHO, one easy way to think of chain catenary is this: When you need it, it won't be there. With enough wind, the angle of pull on the anchor will be the same for chain and rope.



If you are concerned, then anchor with enough scope (chain or rope) so the "lifted shank angle" is still significantly less than the shank-to-fluke angle. That way the flukes aren't getting torqued out of the bottom sand or mud.

Where we anchor in 10 feet of water (roller is 5' over the water, sand bottom), I really like 115 feet of chain on one anchor (60 lb Manson Supreme), 75 feet of rope & 30 feet of chain on the second anchor (40 lb Bruce), snubber on the chain, and a riding sail to keep the boat from tacking (5 degrees versus 120 degrees). Winds have hit 70 mph in a passing storm. I use the second anchor if we are going to be away from the boat for awhile. The Manson is set at 1,500 rpm for 10 minutes. (We previously used a 60 lb CQR. 1,200 rpm would set it, but 1,300 rpm would break it out every time.)

The one time this past summer when the Manson didn't set, having all-chain and an electric windlass meant it took less than 10 minutes to easily raise the anchor, motor forward, and try again. When soloing, it also means I don't have to leave the helm after departure, to coil the rope back into the anchor locker.

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Last edited by Bene505; 11-10-2013 at 10:13 AM.
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  #37  
Old 11-10-2013
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Re: Caternary & Chain...

Quote:
Originally Posted by Maine Sail View Post
I think this data only serves to confirm what Peter Smith has been saying for years, put the weight in the anchor, not the chain....
Agreed. It also supports Alain Fraysse's point that kellets don't help in heavy air, only in light air.
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  #38  
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Re: Caternary & Chain...

While there is no doubt that a static analysis will show that there is little difference between an all chain rode vs all line rode under higher wind conditons, I question the conclusions under dynamic loading. For example, the boat will "hunt" and even with a rather mild 150 pound pull from an all chain rode, that will cause the boat to move toward the anchor until the next wind gust hits. Does this help or hurt the loading assuming that an adequate snubber is involved?
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  #39  
Old 11-10-2013
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Re: Caternary & Chain...

Quote:
Originally Posted by mitiempo View Post
......And who really has swinging room for 10-1 anyway?
If we know it's going to blow, we will anchor further out so we have the room. We sleep at anchor almost every weekend. Love it. We have 200ft of 1/2" chain and usually find a 15' anchorage with 5' of freeboard and drop it all, if wind is going to be above 15kts. That's our rule of thumb. I have no problem taking a longer dinghy ride.

Anything under 10 kts and I practically don't even have to set the hook. Just lying chain on the sea floor and we swing around the catenary, not the anchor. I've seen on the iPad anchor alarm that we've swung 180 degrees and have not even dragged the catenary back to the anchor itself. Really interesting to see. All should get one of these to really understand what's happening down there.

We sat outside of Menemsha this past summer, where you do not want to be in anything from the West through any Northern sector. It was forecast to be SW at 15 overnight. Naturally, it swings to the NW and picks up to 20kts, which pushes 2 to 3 ft seas into the anchorage. We had all the chain out and never moved an inch on our POS CQR. More scope or no stop.
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  #40  
Old 11-10-2013
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Re: Caternary & Chain...

Quote:
Originally Posted by Minnewaska View Post
Just lying chain on the sea floor and we swing around the catenary, not the anchor.
Vocabulary is important. Catenary doesn't have anything to do with what you describe. Catenary is the sag due to weight in a structural element under tension. What you are describing is a combination of the weight of chain and friction of the chain on the bottom.

What you have experienced absolutely happens in light air, with "light air" depending on the weight of the chain, length of the chain, weight of the boat, and windage. This is the scenario where a kellet will actually provide some value.
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