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Just read an interesting piece on anchor snubbers in the latest Practical Sailor. What really jumped out at me was not about snubbers but rather just how little load was required to lift the last link of chain off the bottom of the ocean and affect the anchor shank angle.

If the chain is laying on the bottom, as people often assume it is, the anchor shank is parallel to the bottom or in optimum holding orientation. When the last link of chain lifts it can change shank angle to match that of the scope being used. If on short scope.......:confused:

PS used a 100' section of 5/16" chain set to a 5:1 scope to test how much load was needed to lift the last link off the ground..

To apply the load they used a chain-hoist / come-along and measured it with a calibrated load cell. They physically pulled the chain to see how much load was required to lift the last link of chain eg: the anchor shank, off the bottom.

The shocker for me was that it took just 190 pounds to lift 100' of 5/16" chain at a 5:1 scope off the ground out of the water. The in water load calculation to do the same, when taking the density of the chain into consideration, would be just 158 pounds to lift the last link off the bottom...

Seeing as I own a digital load cell and have physically measured the loads of our 36' sloop at 140 - 218 (218 was peak loads) pounds of load in 17-19 knots the idea of chain holding your anchor on the bottom is really considerably less than where I and many books and experts suggest it would be....? Just 17-19 knots on our boat is enough to lift our chain at 5:1 !!!!!:eek: 17-19 knots is not even a stiff breeze.......

I actually just ran the numbers through an anchor load calculator and it does not show the chain lifting until a load applied of 242 pounds yet based on the PS actual test data it takes just 158 pounds of load to do this... Does this mean that all the theoretical data we've been using for years has been skewed???? It would be one thing if it was skewed in the safer direction but it has been skewed to the unsafe direction....

This means the wind conditions to affect anchor shank angle, with all chain, seem to be considerably lower than originally thought...

So if I am anchoring at 5:1 with 100' of 5/16" chain in approx 17' of water it will take just 17-20 knots, on our boat, based on actual measurements, to begin to lift the chain so the anchor shank angle is affected.

Interesting stuff to say the least and certainly some interesting data to ponder........

Quote: Practical Sailor

"We fixed one end and then tensioned the chain with a come-along until the last links at the lower end had lifted free of the ground. Lifting this required a load of 190 pounds, which translates to 158 pounds in the water. Based on data from last year’s test (PS, May 2012), this would be the equivalent of about 15 knots of wind on a 40-foot boat anchored in about 15 feet of water with 100 feet of 5/16-inch chain."


We've all heard the old axiom that 5:1 on chain is okay but 7:1 on rope/chain rode is needed. With this physically tested & measured data it appears that this is simply not entirely true..

It seems prudent that scope should be set irrespective of all chain or rope/chain rode because chain alone really will not help shank angle when you really need it most, in high winds...??
 

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Now we know what doesn't work.

What *does*?

Kellet?
Heavier chain?
More scope?
Better anchor?
Longer snubber?
All the above?
 

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Discussion Starter #3 (Edited by Moderator)
Now we know what doesn't work.

What *does*?

Kellet?
Heavier chain?
More scope?
Better anchor?
Longer snubber?

All the above?
I think the bolded items will be the most beneficial. A kellet can help prevent sailing at anchor etc. but in a storm the only things that will reasonably work IMHO are:

*Buy the best performing anchor your money can buy (there are lots of great anchors out there today compared to just 10 years ago)

*Use proper setting technique

*Know your bottom and choose the correct ground tackle

*Be prepared to quickly deploy back up tackle

*Use an anchor alarm

* Use GPS cookie trails as PROOF you stayed put when that other clown hits you and then tries to claim it was you who dragged!! (never know when you might need them for insurance purposes) Our GPS is ALWAYS on & laying trails when at anchor!!!

*Use proper calculations for scope and don't forget tides and bow height

*Check your set/setting technique with a strong power set by backing down at full throttle. If your sailboats engine can drag or un-set your anchor, by backing down hard, YOU ARE NOT SET....

*Recheck/power-set again before you go to bed

*If the wind shifts power-set in the new direction to re-test your new set direction. Some anchors are very poor re-setters..

*Use as much scope as you can for the swing room you have

*If you don't feel comfortable with how much scope you can lay, a kellet can certainly help, in moderate winds.

*Get where you are going earlier in the day not later.....

*If you don't feel comfortable with the scope you can lay & swing to, move on......
 

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Funny, I just read an interesting letter in Practical Sailor about batteries.

Written by some guy who owns Compass marine :)

Nice article MS.
 

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This data is interesting.

Even if the last link is off the bottom, I would think that the angle at which the chain meets the anchor shank would be more horizontal with a weighty rode like chain than rope. So I'm postulating that even though the chain is "off the bottom" it is just barely off the bottom at the shank and therefore pulling mostly horizontally.

What would be of interest is what that angle is. You could then calculate the horizontal (good) and vertical (bad) components of force on the anchor.

All that said Maine, I'm surprised at this data. When I look down over the bow in a blow and the chain is bar tight, I'm getting even less sleep than before. And to argue against my hypothesis, I guess if it's bar tight, it's a straight line down to the anchor, so the angle is the angle no matter what the rode.

Maybe the real benefit is that in real life, it's not a straight even pull like a come-a-long. And as you swing back and forth, yanking on everything, the chain absorbs the shock before jerking the anchor out?
 

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Didn't read the article. Were they lifting the chain straight up? If so, I would think that the dynamics of a boat pulling on the chain would be different. I would expect it to take more effort to lift the last link when pulling at a 5:1 angle (11.5 degrees).
 

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What would be of interest is what that angle is.
Easy enough to figure out...



When a=1 and c=5 (a 5:1 scope), the angle at A is 11.5 degrees. Given that a link of 3/8" chain is about 1.75" long, that means that the last link would be lifted less than 3/8" off the bottom. At least, until the shank of the anchor also starts lifting.
 

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Discussion Starter #8
Easy enough to figure out...



When a=1 and c=5 (a 5:1 scope), the angle at A is 11.5 degrees. Given that a link of 3/8" chain is about 1.75" long, that means that the last link would be lifted less than 3/8" off the bottom. At least, until the shank of the anchor also starts lifting.

The important part is that this "lifting" starts at just 158 pounds at 5:1 with 5/16" chain, a very common size on 30-40 boats. On our boat, a 36 footer, we see peak loads of 218 pounds in 17-19 knots and the loads vary up and down between 140-218...... Get above 25 knots and these loads escalate, rather dramatically....

I have never believed, based on my own all-chain experience, that chain gave the caternary one desired when the winds get blowing or when you really need it...

I did not however believe the loads were so small as to when you began to affect shank angle. I find it rather shocking, and reassuring, that I have always believed in scope first before caternary, when you really need it most......

I think this, and the previous data conducted by PS, really points to longer scope and longer and more elastic snubbers...

We know from the previous data that the shock loads increase dramatically as scope is shortened.....
 

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Note that the article was writen by a multihull sailor. There are several reasons why that happend:
* The lighter the boat, the more you feel the chain snap tight. Not that force is greater, but you are more aware of it.
* Multihulls commonly anchor in shallower water, because they can. Perhaps the only free spot in a crowded anchorage is thin. Perhaps there is cove no one else can enter. Either way, multihulls often have less chain out.
* Shallow water gets rough first; some cats have been lost because the owners forgot this. It doesn't matter if you have 2' draft, if the water is <10' it will start breaking fast.
* Multihulls use a bridle/snubber EVERY TIME, even lunch breaks. Thus we tend to be rather obsesed about the best answer. It is also very reasonable for multihulls to use long bridles.
* We tend to like G43 chain to save weight. We have good anchors but would rather not get rediculous on weight as a solution.

The math is the same, I'm just saying the subject is more interesting to cat sailors. A 2' chop in 5 feet of water with only 50' of chain out gets pretty jerky. NO catenary. A 25-30 snubber really takes the sting out.

I too have started running bridle lines down the side decks when in an exposed anchorage; it allows for a long bridle in shallow water. Not always needed, but I often anchor in dubious holding ground and the less the ahchor is horsed around, the better.

Sail Delmarva: Long Bridles
 

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Now I’m really confused. If it takes so little of a force to lift chain off the bottom, what is the advantage of chain over rope rode? I have a 34’ boat weighing 15,000# and was considering ¼ BBB coil all chain rode for the west coast of Mexico. Can I get by with a chain/rope combo and save the weight on my bow?
 

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Now I’m really confused. If it takes so little of a force to lift chain off the bottom, what is the advantage of chain over rope rode? I have a 34’ boat weighing 15,000# and was considering ¼ BBB coil all chain rode for the west coast of Mexico. Can I get by with a chain/rope combo and save the weight on my bow?
Anchoring in the presence of coral can make short work of any rope rode... I think that alone would push me to all chain in those areas..
 

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Now I’m really confused. If it takes so little of a force to lift chain off the bottom, what is the advantage of chain over rope rode? I have a 34’ boat weighing 15,000# and was considering ¼ BBB coil all chain rode for the west coast of Mexico. Can I get by with a chain/rope combo and save the weight on my bow?
Anchoring in the presence of coral can make short work of any rope rode... I think that alone would push me to all chain in those areas..
Point taken about the coral, but George raised an interesting point.

I have a 22lb Danforth and 20' of chain, the balance of my ground tackle is rope. If it takes so little force to raise the chain off the bottom, am I actually better off with this setup as the rope will act as a shock absorber in rough conditions?

ex. anchored in 10 feet + 3ft to the bow roller at 7:1 is 90 feet of rode out, 70 feet of which is rope. That's one long snubber.

My boat is a 30 footer rated at 10,300 lbs, probably over 11,000 fully loaded and all tanks topped off.
 

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As far as I know, there are no coral reefs on the Pacific side of Mexico. Rocks yes, coral no. So if I don’t have coral and I do have 50-100’ feet of chain for chafe protection on rocks, then, by Maine Sail’s calculations, and 7:1 scope (and a Rocna or Manson anchor). I should be o.k. without the weight of all chain?
 

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I think the bolded items will be the most beneficial. A kellet can help prevent sailing at anchor etc. but in a storm the only things that will reasonably work IMHO are:

*Buy the best performing anchor your money can buy (there are lots of great anchors out there today compared to just 10 years ago)

*Use proper setting technique

*Know your bottom and choose the correct ground tackle

*Be prepared to quickly deploy back up tackle

*Use an anchor alarm

* Use GPS cookie trails as PROOF you stayed put when that other clown hits you and then tries to claim it was you who dragged!! (never know when you might need them for insurance purposes) Our GPS is ALWAYS on & laying trails when at anchor!!!

*Use proper calculations for scope and don't forget tides and bow height

*Check your set/setting technique with a strong power set by backing down at full throttle. If your sailboats engine can drag or un-set your anchor, by backing down hard, YOU ARE NOT SET....

*Recheck/power-set again before you go to bed

*If the wind shifts power-set in the new direction to re-test your new set direction. Some anchors are very poor re-setters..

*Use as much scope as you can for the swing room you have

*If you don't feel comfortable with how much scope you can lay, a kellet can certainly help, in moderate winds.

*Get where you are going earlier in the day not later.....

*If you don't feel comfortable with the scope you can lay & swing to, move on......
Nice list! I'd add - oversize the anchor by a considerable margin. Don't go with minimum advertised weight for your boat.

The triangle example shows a right triangle which is actually 3-4-5 a 5:1 triangle with anchor line as the hypotenuse would look a lot different if trying to picture the chain and caternary. Using a 3-4-5 triangle, a 12' depth would only require a 20' anchor line. Showing a scaled graphic would accentuate the point that the actual lift at the end of the chain is quite small, not as if the anchor is being yanked out.
 

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I know this will sound somewhat flippant and it is typed with a smile on my face but how is that the Womboat doesn't simply drag all over the anchorage every time we drop anchor ?

You are free to consider that question rhetorical. :) but ....

Seriously though. I take anchoring very very seriously indeed. Even dropping a lunch pick I take great care but even so in the three keel boats that I have spent the most time on the first had some fifty feet of chain plus rope on a Danforth, the second fifty metres of chain plus rope on a CQR and then later a Rocna while the third has ninety metres of chain plus rope on a Bruce.

Yes there have been plenty of times when we've had to re anchor after failure to set but once set we've very rarely had any problems and in almost every case of dragging it has coincided with my failure to deploy the snubber.

Yes, I know, preaching to the converted but the efficacy of a snubber cannot be underrated.
 

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Frankly I have never bought the heavier chain argument. The weight of chain just isn't enough to matter in heavy conditions. I have swapped to smaller chain but higher test, and a much larger anchor.

With anchors today generating multiples of their own weight in holding power, the best place to put that weight is in the anchor not the rhode. See Steve Dashew's 120lbs anchor on a 64' boat as an example.
 

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Frankly I have never bought the heavier chain argument. The weight of chain just isn't enough to matter in heavy conditions. I have swapped to smaller chain but higher test, and a much larger anchor.

With anchors today generating multiples of their own weight in holding power, the best place to put that weight is in the anchor not the rhode. See Steve Dashew's 120lbs anchor on a 64' boat as an example.
I agree. One theory is that catenary provided by the chain disappears when it is needed most - but that is a very small load in PS's test. Dashew agrees with this as does someone named Smith.:)
 

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While I believe the data from this test and some good points have been made, I think it fails to continue up the curve.

The force necessary to lift the last link at the shank is one thing and very telling. However, keep going. What is the comparable force to full straighten a rope rode vs. 5/16 chain?

To further make this point, if 7:1 all rope rode will theoretically hold, what force is necessary to get 5:1 chain to pull to this same angle? I think that would reveal the value of chain.
 

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Discussion Starter #19 (Edited)
While I believe the data from this test and some good points have been made, I think it fails to continue up the curve.

The force necessary to lift the last link at the shank is one thing and very telling. However, keep going. What is the comparable force to full straighten a rope rode vs. 5/16 chain?

To further make this point, if 7:1 all rope rode will theoretically hold, what force is necessary to get 5:1 chain to pull to this same angle? I think that would reveal the value of chain.

This was approx 30 knots at low tide with very, very heavy mooring chain, IIRC 3/4" long link mooring chain. This chain weighs 5.3 pounds per foot, the mooring ball and swivel & shackles weighs another 20-25 pounds.......




This anchor roller was folded like a pretzel by the shock loading of an all chain rode. The owner lost power on a lee shore and did not have time to deploy his snubber. He no longer uses 2 micron primary fuel filters...;)


Yes it takes lots of strength to fully straighten chain or attain infinite scope but to change shank angle, or to impart shock loading, that certainly can and does happen.,


I always liked this photo by Peter Smith:

"What catenary? Anchored in 50-60 knots wind at Deception Island, Antarctica – even in 8 m depth, this 12 mm chain at 6:1 scope is nearly bar-tight and any apparent benefit from catenary to the Rocna anchor at the end of the rode has long since disappeared."



Typical anchor chain has numerous benefits, but providing adequate caternary, in storm conditions, is not one of them....

I suppose if you want to use chain like this then you would have some caternary, but most sailors don't want to anchor with this stuff. Hell most mooring owners would balk at the per-ft price on this stuff... I use 30 feet of this stuff on my "everyday" mooring. My storm mooring uses significantly larger bottom chain with the bar across the link. Still, in a hurricane or bad Nor' Easter, there will be little to no caternary even on my storm mooring....
 

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The triangle example shows a right triangle which is actually 3-4-5... Showing a scaled graphic would accentuate the point...
True, but that was the only picture that I could find easily to illustrate the calculations I was doing. I calculated the angle at A based on a 5:1 ratio. That is, a triangle where length of "a" would be 1, "c" would be 5, and "b" would be 4.9. That angle, when the chain is straightened out, would be 11.5 degrees.

Of course there will be some catenary, so in reality the angle at A would be somewhat less. Still, the point remains that the angle at A, even at "only" a 5:1 ratio, is pretty small.
 
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