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Old 04-02-2011, 19:34   #46
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You're just begging the question. If the chain is still flat on the seabed at the anchor, the rode's not under much load. Obviously. Under "heavy conditions" in the context of small boats, in anything other than deep water, any reasonable weight of chain will be lifted near as makes no difference to bar taut - especially by dynamic forces. The effect of catenary, and kellets and the like, is as good as worthless. Your only friend is scope - plus shock-absorption to smooth out the peak dynamic loads.
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Old 04-02-2011, 20:26   #47
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Originally Posted by craigsmith View Post
You're just begging the question. If the chain is still flat on the seabed at the anchor, the rode's not under much load. Obviously. Under "heavy conditions" in the context of small boats, in anything other than deep water, any reasonable weight of chain will be lifted near as makes no difference to bar taut - especially by dynamic forces. The effect of catenary, and kellets and the like, is as good as worthless. Your only friend is scope - plus shock-absorption to smooth out the peak dynamic loads.
One of the most critical "anchoring" applications is that of the climbing rope an ice climber uses to attach himself to has anchors, in this case, screws placed in the ice. Though the screws themselves have very high rated strengths, they can be no better than the ice they are in. Ice climbers wear razor sharp crampons on their feet and swing sharp axes, either of which could damage or sever the rope with one blow. Falls are typically longer than in rock climbing, and the climbers are heavier because of the added winter gear.

Do they use more robust ropes than rock climbers or thinner ropes?

The answer is thinner. Though breaking a rope might be possible, pulling an anchor is far more likely and many thousands of times more common; a thinner more elastic rope addresses the greater risk. But the "horsing around at anchor" argument is valid too; rock climbers use a slightly stiffer rope in part because with greater stretch comes an increased risk of striking a ledge, as the fall is longer.

Always a compromise. Any failure due to chafe will be blamed on a fiber rode, though it is generally a poor lead that is to blame. Damaged bow sprits are often blamed on the stiff nature of chain, though a snubber could remidy that. Anchor drags are generally blamed on the anchor, though any combination of rode and setting practice could as easily be at fault. Gear failure among rock climbers and ice climbers is extreemly rare and is nearly always the fault of a rigging error or of not understanding the entire anchoring system (avalanches are an exception).

I suspect climbers and sailors that take the time to really understand their system and its limitations are a pretty safe group. I know that my anchoring gear has limitations and I avoid them; if I cruised more widely I would have heavier gear. But I'm certain I would have sufficient fiber in the system to cushion the snatch loads chain can generate.
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Old 07-02-2011, 00:16   #48
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THINWATER'S parallel

Yes, anchoring in different applications is a parallel having the same physics phenomenon. Static pull, velocity recovery (like from a fal), or jerk, which is the physics equivalent of the "derivative" or rate of change of accelelaration, apply regarding the disturbance of an anchor.

Dynamics overwhelm the statics when a particular situation is immenent in causing the anchor to stay or move.
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Old 07-02-2011, 14:32   #49
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Please, everyone look up "begging the question." It's not what you think.
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Old 07-02-2011, 14:50   #50
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My point is that when ALL of the rode lifts off of the bottom right up to the anchor attachment point then any further pull will endeavor to lever the anchor out.
If the rode is lying on the bottom then it's not very windy. If a taught rode "levers the anchor out," then more scope is needed.
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Old 07-02-2011, 15:14   #51
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I think Craig has a point that is missed:

When we talk in terms of G4 chain as a common requirement and labor over load rated shackles, we are saying that we expect a load up near the SWL to occur and be common in severe weather. If we apply 2,600 pounds of tension (buoyed up by sea water) to 100 feet of 1/4-inch chain, I promise you it will be arrow-straight. Simple calculations (we do these calculations when pretensioning tower cables) suggest that it will be deflected about 3 inches at the midpoint, and less in the surges. There won't be any chain on the bottom, whatever the scope, unless that scope exceeds 20:1. At that point, there still really isn't much chain on the bottom, but the angle is so low, it matters little.

When the chain is in this stretched out posture its stretch potential amounts to a fraction of an inch, if you do the trig. The only shock absorption will be from translational movement through the water, and that won't be much.

I don't wish to give my options this time, just to share a bit of math that the group can ponder. I doubt many of us wish to be diving by the anchor when the wind is at 70 knots.

Cable Sag Error (Catenary Curve Effect) Calculator
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Old 07-02-2011, 17:44   #52
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Good job Thinwater! Thanks for the technical info.
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Old 07-02-2011, 18:05   #53
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Speaking as an all chain with Bruce anchor and 10ft snubber I think your talking a load of hot air Craig.... its one thing to push your product here but there's newbies here as well and I'd hate to think someone could lose their boat or worse listening to a sales pitch...
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Old 07-02-2011, 18:41   #54
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Geesh, Boatman. What's so dangerous about Craig's advice? The advice about poly vs. nylon (spliced to plenty of hi-test chain)? The advice about using plenty of scope? Or the recommendation to use a snubber?
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Old 07-02-2011, 19:00   #55
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Please, everyone look up "begging the question." It's not what you think.
If that was aimed at me I meant what I said, the post I was addressing was essentially based on a circular argument that assumed its own point that the chain never left the seafloor. Apologies if not. Sorry for the confusion.
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Old 07-02-2011, 19:15   #56
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No need to apologize, I'm not mad at you for being confused. I am just being a doctrinaire fart. Anyhow I think we basically established that polyester is an acceptable rode material, as are nylon and chain. Each has advantages and disadvantages. Nylon is very stretchy, light and cheap. Polyester is light and cheap too, but a little less stretchy. Chain is expensive and heavy, but the least likely to chafe through in a storm.
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Old 08-02-2011, 09:14   #57
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Please, everyone look up "begging the question." It's not what you think.
Iím confused.
It seems to be exactly what I think.
Let me google that for you

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Old 08-02-2011, 16:45   #58
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There was a YM test on that:

- swivels went first,
- then the shackles,
- then the chains.

We do not use swivels. One weak link is good enough. ;-)

b.
I can attest that 1/3 of that is true: this week a South African sloop (named knot2fast or something like that) went to to the rocks here because a ss swivel parted during a 40 kt storm.

The couple had been cruising for 3 years, so they aren't newbies.
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Old 08-02-2011, 16:55   #59
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There was a YM test on that:

- swivels went first,
- then the shackles,
- then the chains.

We do not use swivels. One weak link is good enough. ;-)

b.
I can attest that 1/3 of that is true: this week a South African sloop (named knot2fast or something like that) went to to the rocks here because a ss swivel parted during a 40 kt storm.

The couple had been cruising for 3 years, so they aren't newbies.
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Old 08-02-2011, 19:33   #60
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What has "newbies" got to do with it? Your South Africans apparently chose a poor quality product. If not, and it was something ostensibly decent like a Kong or WASI, then that would be unprecedented and maybe you'd like to get more details rather than posting vague alarmist anecdotes.

Barnakiel's statement is just wrong, fully five of the connectors in the YM test were as strong or stronger than the chain, precisely as would be expected.
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