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Old 06-04-2016, 06:34 PM   #41
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Chain on the end of the anchor shank actually inhibits anchor penetration because it slices into the bottom w dificulty. Anchor penetration is better w a short length of cable (2 or 3') because the end of the shank goes into the bottom bette
And you know this how? So I take the shackle also inhibits "penetration"? Have you ever actually observed how chain interacts with mud and sand? Do you have any concept of the forces at work when you set an anchor and the effect on the rode? Or at least considered why no one does this?
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Old 06-04-2016, 08:00 PM   #42
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Good questions George,
Go back to Steve's (Panope) anchor vids and see the rode pulling up at maybe 45 degrees and the end of the shank obviously being pushed down onto/into the seabed. The shank not at 45 deg like the rode at all. People don't guard against this because they don't know the shank does this. Most people think (as I did) that the shank is well above the sea floor (more in line w the rode) before I saw Steve's vids.

Re the shackle see the thread "Shackle bolt in shank or chain" post #1. The pic is upside down but you can see the small and narrow shackle that I bought through XYZ anchors. Minimal size/profile so will penetrate the bottom better allowing the shank to run deeper .. probably allowing the anchor to dig/penetrate deeper. There is some speculation I admit but see the evidence and draw your own conclusions. In the pic you can see a recent rode of mine that employed the short cable.
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Old 06-04-2016, 08:46 PM   #43
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Having dove down on plenty of anchor rodes and watching the videos...if the shank and chain do not penetrate...the substrate is hard enough that peneration at that point is not necessary, necessary holding power is achieved. If the bottom Is softer, needing more penetration...it will..... even with large shackles and chain....

Anchors are designed to dig, even with shackles and chain to whatever depth they need to....to acheive the necessary holding.....yes at some point they dont....but that isn't because of the rode...it is because of the anchor design and or scope or bottom material.
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Old 06-04-2016, 10:26 PM   #44
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Originally Posted by Capt.Bill11 View Post
Once the chain come bar tight there is no more centenary effect.
As I recall, and if I had time I would confirm before posting but I don't so for now my possibly flawed memory will have to do, the physics of the situation dictates that the force required to lift the first 5' of chain off the bottom of a level sea floor 60' deep, with 420' of chain rode (or any other 7-1 scope of any appreciable length), is greater than the breaking strength of any typical anchor chain.
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Old 06-04-2016, 11:28 PM   #45
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As I recall, and if I had time I would confirm before posting but I don't so for now my possibly flawed memory will have to do, the physics of the situation dictates that the force required to lift the first 5' of chain off the bottom of a level sea floor 60' deep, with 420' of chain rode (or any other 7-1 scope of any appreciable length), is greater than the breaking strength of any typical anchor chain.
I once had a conversation with an architect/ engineer friend of mine about catenary. He was designing a screened bird enclosure that was constructed with poles and steel cable covered with netting. It was big and the cables all had catenary. I asked him why he didn't just pull them tight. He said they would break before you could pull the catenary out of them. He could do the math which is way beyond me.
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Old 06-04-2016, 11:56 PM   #46
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Chain and shackles won't burry in a hard bottom of course.
My reference was to Steve's anchor setting vids and the bottom was quite soft. And soft bottoms benefit most from penetration.

Yes Travler and HopCar,
There are many posts about chain rodes pulled "bar straight" and I thought it was about time that myth got exposed. Of course this is in favor of chain rodes and I usually don't beat the drum for chain but the more myths we can bust or truths we can uncover the better.
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Old 06-05-2016, 12:51 AM   #47
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As I recall, and if I had time I would confirm before posting but I don't so for now my possibly flawed memory will have to do, the physics of the situation dictates that the force required to lift the first 5' of chain off the bottom of a level sea floor 60' deep, with 420' of chain rode (or any other 7-1 scope of any appreciable length), is greater than the breaking strength of any typical anchor chain.
I have given this a little more thought, and stand behind my conclusion, above, that the pull on an anchor at the end of a 7-1 scope all-chain rode will always be horizontal (if the bottom is). But, there is an exception and it has to do with scaling. If the boat (and its anchor/chain/rode) were a scale model, the chain could be strong enough to lift off the bottom. But, scaling up to real trawler size prevents (fortunately) that same result. Even Divinci got in trouble with scaling -- his helicopter would work if small enough but could never get the lift necessary to overcome gravity at any practical size. A tangent to another thread concerned seaworthiness as a function of size. I don't remember who argued what, but I think someone forgot about the consequences of scaling.
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Old 06-05-2016, 06:37 AM   #48
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Originally Posted by MYTraveler View Post
As I recall, and if I had time I would confirm before posting but I don't so for now my possibly flawed memory will have to do, the physics of the situation dictates that the force required to lift the first 5' of chain off the bottom of a level sea floor 60' deep, with 420' of chain rode (or any other 7-1 scope of any appreciable length), is greater than the breaking strength of any typical anchor chain.
Ok, so the more important question, with proper anchor and chain size, at what scope do you start lifting the first five feet of chain off the bottom when anchoring in 60' of water?

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Old 06-05-2016, 07:15 AM   #49
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How Much Chain Rode

Ted
To answer your question the catenary has to be calculated. In our discussions beginning this year I designated this load as the "ultimate catenary load" to distinguish from the "ultimate load with stiff rode".
Data needed to calculate the catenary are
-) height / water depth (60')
-) specific chain weight per length
-) length of the chain
Results of the calc would be the tensile force whose horizontal component gives the holding force keeping our vessel in place.

To be more precise: as long as the chain length exceeds those 60' water depth the scope at which the chain starts to lift at the ground (ultimate catenary) depends on the horizontal force acting at the chain ...

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Old 06-05-2016, 07:23 AM   #50
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Chain and shackles will bury in a hard bottom....they will saw into coral too.

Usually they dont bury in a hard bottom, not because they cant, it's because they usually don't have to.

If a big old fat anchor can bury, why can't a shackle and chain ?
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Old 06-05-2016, 08:25 AM   #51
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Ok, so the more important question, with proper anchor and chain size, at what scope do you start lifting the first five feet of chain off the bottom when anchoring in 60' of water?



Ted

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Some figures, all for 60' depth, specific chain weight 1.55 lb/ft, zero slope angle at ground.
-) slope 3:1 (180' chain): holding force 371 lbf / chain load (tensile force) 464 lbf
-) 5:1 (300 ft): holding 1114 lbf / load 1207 lbf
-) 7:1 (420 ft): 2228 lbf / 2321 lbf
-) 9:1 (540 ft): 3713 lbf / 3806 lbf, increasing suddenly to 7519 lbf if chain becomes stiff
-) ...
Figures will differ if specific chain weight changes.
The more chain is out, the higher is the horizontal force (holding force) needed to lift the last feet of chain. But the resulting tensile load might exceed the chain strength if a sudden gust pushes us back and the chain becomes stiff ...


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Old 06-05-2016, 08:50 AM   #52
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chain + line is really American way you never saw that in Europe
Most sailing boats here in the old world are doing it the "American way", 10-50 feet of chain followed by a nylon rope. While the majority of full displacement power boaters here in Europe don't care of the chain weight at the bow, most of them have an all chain rode and will apply a snubber for shock absorbance.



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Old 06-05-2016, 09:08 AM   #53
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Makobuilders,
I'm going to change my response to your question a bit. If you put your hunk of studded chain about 10' up from the anchor it would probably be close to ideal.
I wonder why you asked this question though because almost nobody here has a ground tackle settup that would retrieve such a rig. One would need a reel type winch.

An easy way to experiment would be to arrange a rope/line, chain ect on a slope approximately the same angle as your typical scope between two fixed points w a little droop in the line. Then attach a weight along the line or whatever and measure the angle of the line at the lower end .. to horizontal. Find the weight position that produces the flattest line at the lower end ... more horizontal.

You don't seem to get it Scott.
Of course chain and shackles are pulled below the surface in/on a soft bottom. It's a matter of degrees. More is better so rode that slices more easily down in the bottom substrate has an advantage. Better is better. That's all. Like dual exhaust is better than one. Just a little better but better.
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Old 06-05-2016, 09:17 AM   #54
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Originally Posted by waddenkruiser View Post
Most sailing boats here in the old world are doing it the "American way", 10-50 feet of chain followed by a nylon rope. While the majority of full displacement power boaters here in Europe don't care of the chain weight at the bow, most of them have an all chain rode and will apply a snubber for shock absorbance.



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So .... Just like us Yanks. That's flattering .. thanks.

Just seems to be a matter of those that care about weight and those that don't. In addition to that trawlers are concieved as heavy .. heavy duty .. skookum .. robust .. strong. All percieved as good and there will be a high percentage of those that think weight is good in a group of trawler skippers. And it even emulates the boats we were named after .. North Sea Trawlers.
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Old 06-05-2016, 04:40 PM   #55
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I have given this a little more thought, and stand behind my conclusion, above, that the pull on an anchor at the end of a 7-1 scope all-chain rode will always be horizontal (if the bottom is). But, there is an exception and it has to do with scaling. If the boat (and its anchor/chain/rode) were a scale model, the chain could be strong enough to lift off the bottom. But, scaling up to real trawler size prevents (fortunately) that same result. Even Divinci got in trouble with scaling -- his helicopter would work if small enough but could never get the lift necessary to overcome gravity at any practical size. A tangent to another thread concerned seaworthiness as a function of size. I don't remember who argued what, but I think someone forgot about the consequences of scaling.
Even if it were true that the last few feet never lift off the bottom or move to the semi-vertical position, which I don't believe to be so, the snatch load would still be transmitted to the anchor, no?
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Old 06-05-2016, 05:03 PM   #56
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Having scanned this thread I did not notice any mention of windlass sizing. If you are intending to up-size the windlass for larger chain, you should also consider the overall weight of the new anchor plus the longest length of 3/8 BBB chain (vertical lift from deepest anchoring location), and make sure you get a windlass with capacity to spare. Having once had to pull up 200ft of chain by hand (using the windlass come along) because of a failed solenoid switch, I definitely do not recommend this approach!!
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Old 06-05-2016, 05:51 PM   #57
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Even if it were true that the last few feet never lift off the bottom or move to the semi-vertical position, which I don't believe to be so, the snatch load would still be transmitted to the anchor, no?
Yes, there will always be jerk load on the anchor (though the catenary acts as a damper), but never in excess of the load the weakest link in the chain can handle. Isn't the real question, though, how to best maintain horizontal pull on the anchor? As for whether the force on the anchor chain can ever be enough to lift the chain off the sea floor, you may be right, but physics suggests otherwise.
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Old 06-05-2016, 08:53 PM   #58
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I think a level pull on the anchor and chain induced catenary is a good thing. But I think it's over sold and over rated. Looking at Steve's vids consistantly showing the anchor shank pointing down on the bottom instead of pointing up the rode speaks volumes about the need or lack of need for catenary. Even though the rode is ramped up at 20 to 30 degrees. Catenary is a good thing but much less necessary than we thought before.
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Old 06-05-2016, 09:16 PM   #59
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Originally Posted by psneeld View Post
Chain and shackles will bury in a hard bottom....they will saw into coral too.

Usually they dont bury in a hard bottom, not because they cant, it's because they usually don't have to.

If a big old fat anchor can bury, why can't a shackle and chain ?
My thoughts also...
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Old 06-05-2016, 09:30 PM   #60
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I think a level pull on the anchor and chain induced catenary is a good thing. But I think it's over sold and over rated. Looking at Steve's vids consistantly showing the anchor shank pointing down on the bottom instead of pointing up the rode speaks volumes about the need or lack of need for catenary. Even though the rode is ramped up at 20 to 30 degrees. Catenary is a good thing but much less necessary than we thought before.
Eric, I think you are only partly right there. Sure, even at quite short scopes, the shanks in Steve's videos did appear to stay down on the bottom, I suspect that was because of the downward force on the shank imposed by the mechanics of the fluke digging down into the bottom. However, once the anchor is set, if the forces on the rode were sufficiently great that the catenary is overcome and the rode does pull directly on the shank in an upwards direction, the subsequent levering action would begin to raise the shank, and therefore also the fluke tip, and a break-out could well follow. So, overall...the catenary IS a really important factor in staying put I would say.
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