Not Getting the All-Chain Thing - Page 49 - SailNet Community
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post #481 of 535 Old 05-15-2019
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Re: Not Getting the All-Chain Thing

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Originally Posted by RegisteredUser View Post
Great stuff...but doesnt stretch
Nor does chain
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Yep...ditch weight of chain...ditch stretchy snubber...go dyneema.
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post #483 of 535 Old 05-15-2019
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Re: Not Getting the All-Chain Thing

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Originally Posted by Minnesail View Post
I think every post on anchoring technique should be preceded by a brief description of what you’re anchoring, and where. Otherwise the information isn’t terribly useful.
Very true, with a few exceptions the dividing line between mixed rode and all chain seems to be very much related to displacement.

Which makes sense. Heavy, boats with lots of systems will barely notice windlas, chain, batteries, generators etc.

Smaller, lighter boats will notice not only the extra weight but the lost space associated with additional systems.

Last edited by Arcb; 05-15-2019 at 06:48 PM.
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post #484 of 535 Old 05-15-2019
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Re: Not Getting the All-Chain Thing

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Irrespective of what anchor is used, if the shank is lifted enough the anchor will break out and drag....
Holding capacity only begins to decline significantly with a scope less than about 10:1. Same with the chain coming off the bottom; not critical unless significant lift.

[This table is for large anchors, but I have tested and published data for many common anchors.]


Of course, once the cable lifts, the anchor also becomes for vulnerable to yawing, which is not often reported. It is probably the greater risk.

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Re: Not Getting the All-Chain Thing

First, I only mentioned Dyneema for fun. That said, I have used it as a chafe leader on a kedge.

a. Dyneema is very wear resistant end-to-end, but most weaves are s__t side-to-side. Abrasion resistance, it turns out (much testing) has more to do with weave than material. That is why most mooring pendants and chafe gear use nylon or polyester webbing; different weave. Only a few covered Dyneema ropes are optimized for side-to-side (NER WR2).

b. To corollary is that the cover must move freely. It is hard to cut or chafe something that is not tensioned and is free to rotate.

My Dyneema leader had a free floating webbing chafe guard. VERY hard to chafe.

And curiously, I use a Dyneema bridle (the rode is nylon). I want the rode to stretch, but I would rather the bridle did not. Think about that.

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post #486 of 535 Old 05-15-2019
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Re: Not Getting the All-Chain Thing

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Originally Posted by pdqaltair View Post
Holding capacity only begins to decline significantly with a scope less than about 10:1. Same with the chain coming off the bottom; not critical unless significant lift.
I assume when you say “scope”, you mean rode length to water depth ratio.

I have always subscribed to a scope of 5:1 unless the weather turns nasty when I will sometimes go out to 7:1. Anchoring at 10:1 in many places I sail would require a rode of 200 metres (650ft). I seriously doubt there are many boats with that sort of rode aboard. As an aside, with my 10mm all-chain rode, that would weigh nearly half a ton. The wind would have to really scream for my boat to lift that much chain

Effectively what you’re saying is that anyone anchoring with 5:1 has significantly declining holding capacity? I would venture to suggest this would be a substantial proportion of sailors. It’s a very commonly used scope.
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Re: Not Getting the All-Chain Thing

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Originally Posted by pdqaltair View Post
...And curiously, I use a Dyneema bridle (the rode is nylon). I want the rode to stretch, but I would rather the bridle did not. Think about that.
I am curious. Love to know your thinking.

BTW, I mused about needing a snubber on a Dyneema rode. I assume it would be required since Dyneema would behave like chain.

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post #488 of 535 Old 05-16-2019
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Re: Not Getting the All-Chain Thing

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...Effectively what you’re saying is that anyone anchoring with 5:1 has significantly declining holding capacity?...
Yes, obviously. If they are using chain, the affect depends on wind strength and water depth (in shallow water, using chain does not actually help, in >20 feet, it helps a lot--it's about the pounds). If they are using rope, it depends on those factors and how much chain leader.

But my point was that this does not happen "when the chain leaves the bottom; there needs to be a >10 degree angle.

Additionally, it depends a GREAT deal on the type of anchor. Fortress, for example, if well set, is affected to a much lesser extent than shown on the graph. Even at VERY short scope (4:1) there is little reduction in holding. Just ask someone who tried to recover one after a 60 kt storm; it's epic.

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Re: Not Getting the All-Chain Thing

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Originally Posted by MikeOReilly View Post
I am curious. Love to know your thinking.

BTW, I mused about needing a snubber on a Dyneema rode. I assume it would be required since Dyneema would behave like chain.
At high load, a nylon bridle stretches, and is no longer an isosceles triangle. This can result in increased yawing. Yes, I have measured it. Additionally, if you are using all-rope, you arguably have too much stretch already.

BTW, if I were using chain (last boat) it would be nylon, of course, and long. Totally different case.

----

Dyneema would be much worse than chain. I tried it once, during testing. Without a snubber you might break a cleat off. I blew a 2-ton load cell when a wake hit me in about 10 knots, but shallow water. BAM. Probably saved my cleats.

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post #490 of 535 Old 05-16-2019
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Re: Not Getting the All-Chain Thing

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Originally Posted by MikeOReilly View Post
BTW, I mused about needing a snubber on a Dyneema rode. I assume it would be required since Dyneema would behave like chain.
Maybe my thinking is skewed - I always use a snubber to damped the noise of the anchor being dragged over the bottom and transmitting the noise up into the boat. For me it’s not about improving the integrity of the rode. My chain is way stronger than the snubber.

This noise transfer would not be evident using dyneema or any other form of rope so why add a snubber?

I just read pdqaltair’s post. Is the fact that light-weight dyneema provides no catenary and also no stretch that caused it to break your load cell? Maybe the springy nylon snubber would improve the quality of the rode in this case. Score a negative for dyneema as ground tackle potential.
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