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post #491 of 535 Old 05-16-2019
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Re: Not Getting the All-Chain Thing

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Originally Posted by pdqaltair View Post
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.
Wow, talk about a smoke screen. I have read this post over and over and canít see the message. I must be really dumb. If youíre saying that 10:1 scope is less likely to drag than 5:1 then I agree, obviously that is correct. But thatís like saying is a Volvo boat going to get there before my boat? Well, obviously.

Oh, never mind. 😏
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post #492 of 535 Old 05-16-2019
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Re: Not Getting the All-Chain Thing

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Effectively what youíre 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. Itís a very commonly used scope.
I don't think that is what he meant. Because of catenary, the relationship between the scope and the angle on the bottom is not linear. 10:1 is the point where the end of the chain lies on the ground no matter what load is on it. There is no practical difference between 10:1 and 100:1.

Between 7:1 and 10:1 for almost all anchoring situations, there is only a little difference in this regard. Not really enough in a practical sense to matter much at all. Maybe the angle increases a degree or two in this range.

5:1 starts to become significantly different from 10:1 wrt to the rode/anchor angle, but again, is still a useful practical scope for ideal setting, holding, and resetting an anchor. However, there is enough of a difference that most people intuitively let out a bit more scope for major weather.

As scope gets shorter than 5:1, the angle to the bottom increases exponentially (actually as a hyperbolic cosine), until at 1:1 it is to a first order 90* and linear.

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post #493 of 535 Old 05-16-2019
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Re: Not Getting the All-Chain Thing

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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 itís 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? ...
Noise dampening is one useful aspect of a snubber, but I view this as secondary to the real benefits. The major reason one needs a snubber with all-chain rode is to act as a shock absorber. Another vital aspect of a snubber is to take the load off the windlass. I would never anchor for more than a few hours without deploying my snubbers (I almost always use a bridle arrangement).

This is why I asked about a snubber with dyneema. Since it doesnít stretch, I assume one would need a snubber of some sort if it was used as a rode.

I always try and deploy as much scope as possible. If I can get to 10:1 (or more), I do. Itís all about angle to the anchor shank/sea bed. The smaller the angle the better. I view 5:1 as minimum for overnight anchoring.

With regard to the benefits of chain in shallower waters, itís true catenary doesnít come much into play. Rather, the range of wind speed/rode angles are much narrower for the effect. But one one benefit of all chain in shallow waters is simple rode weight and friction.

As anyone who anchors in shallow waters with all-chain knows, most of the time we swing from our chain, not the anchor. Dragging around all that bumpy chain creates a significant drag which also acts as a dampener. While not the same as catenary, it is similar in effect.

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post #494 of 535 Old 05-16-2019
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Re: Not Getting the All-Chain Thing

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Originally Posted by Cassidy View Post
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.
A snubber is not just to preserve the ingetrity of the rode or reduce noise. Assuming it is long enough it:
* Reduces the load on the ground tackle by 3-5 times (based on testing by numerous researchers. Rember that the ABYC table is designed to stress the tackle to the WLL in a worst case situation unless a snubber is used.
* Increase anchor holding in worse case. The anchor will only hold peak loads IF the sand is perfect and the boat doe not yaw, if there is catenary in the chain, or if there is some other shoc absorption. Otherwise, dragging is probable.

If you have not seen these extreme loads, it is probably because you have not experienced a worst case (shallow water, steep waves, relatively short scope).

---

And no, I was not suggesting Dyneema rode. That was just for fun. Yes, Dyneema just transfers the impact, like hitting a brick wall. I can see the use for VERY long rodes, like platforms. Ships use it for dock line, BUT they have either hydraulic winches that constantly maintain tension, OR they use nylon snubbers on the ends.

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post #495 of 535 Old 05-16-2019
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Re: Not Getting the All-Chain Thing

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Originally Posted by Cassidy View Post
Wow, talk about a smoke screen. I have read this post over and over and can’t see the message. I must be really dumb. If you’re saying that 10:1 scope is less likely to drag than 5:1 then I agree, obviously that is correct. But that’s like saying is a Volvo boat going to get there before my boat? Well, obviously.

Oh, never mind. ��
No smoke screen. The math gets complicated, because the effect of the chain catenary is a function of the weight of chain out. In fact, the formulas are not that complex, but there are many variables. It's really to much to post in a forum. It's more like a chapter, with graphs.

As a rule, as the water gets deeper, there is more chain, and thus the catenary is more effective. Over 20 feet, catenary works very well even in strong winds; it's hard to lift that much chain if the scope is at least 7:1. Under 5 feet chain doesn't work differently than chain once the wind hits 25 knots; it lifts off the bottom in under 15 knots. In between, it is, well, in between. I've spent a LOT of hours on the bow with a load cell, and a lot of hours diving, checking theory against data.

What is critical is the angle at the bottom. Less than about 10 degrees, not much change, more than 10 degrees anchor holding drops off (except for Fortress, which drops very slowly). Finally, all anchors are more vulnerable to weakening due to yawing when the chain is off the bottom, which is probably the actual cause of most dragging of well-set anchors.

---

I do a lot of anchoring testing. This spring I did a series of test on riding sails (3 designs). Rode types, kellets and yawing. Just yesterday I was testing several variations on bridles, though that was probably trimaran-specific. It is not a simple topic, though most of the time you can just chuck the anchor and 5:1 scope and all is well. But optimizing is complicated. You could say to same of sailing, of course. That Volvo crew could make any boat go faster!

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post #496 of 535 Old 05-16-2019
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Re: Not Getting the All-Chain Thing

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This spring I did a series of test on riding sails (3 designs).
Could you share any of that with us?

I'm thinking I need to make a riding sail.

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Re: Not Getting the All-Chain Thing

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Could you share any of that with us?

I'm thinking I need to make a riding sail.
That was for Practical Sailor. I just mailed one of the test sails back to the vendor yesterday. I don't know when the article will print.

There is no 1-paragraph answer. It depends on the boat and what fits. However, I suggest one of the twin luff V-shaped sails; they outperformed traditional single luff sails in every way and are much more stable in a strong wind. My personal choice, if I were going to make my own, is diamond of fabric laid over the end of boom, with the boom then elevated. Paratech designed it, but never marketed it. The Fin Delta is a neat commercial option, more suitable if you have a bimini, but far more complex to build.

See top of page 29. https://www.seaanchor.com/wp-content...structions.pdf

A few of my notes, just as I began testing. Sail Delmarva: Riding Sails

They really do help, even more than chain, once the wind gets up. Yawing has always scared me, since it loosens the anchor.

Note for single luff riding sails: They are NOT set on the center line. The front corner should be offset at least 4-6 feet from the leach.

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Re: Not Getting the All-Chain Thing

That fabric laid overt the boom looks interesting. It'd be really quick to rig, so if that works at all it'd be pretty slick.

I'm curious why lifting the rudder would help. I would think the rudder would resist side-to-side motion.

Like I said, my boat swings all over at anchor. The stack pack acts like a quadruple reefed sail, so once it gets moving it really goes. It can be quite alarming when you're swimming off the back of the boat...

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Re: Not Getting the All-Chain Thing

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I'm curious why lifting the rudder would help. I would think the rudder would resist side-to-side motion....
Yawing is cause by the center of windage being farther forward than the center of lateral resistance. Adding a riding sail moves the windage aft. Lifting the rudder moves the CLR forward.

Yes, it really helps. A lifting rudder should always be raised. A lifting centerboard can go either way (some times up is better, sometimes not). The absolute WORST is CB up and rudder down.

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post #500 of 535 Old 05-16-2019
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Re: Not Getting the All-Chain Thing

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Originally Posted by pdqaltair View Post
If you have not seen these extreme loads, it is probably because you have not experienced a worst case (shallow water, steep waves, relatively short scope).
Quite right, I would not anchor in those conditions and if conditions changed while I was anchored, I would leave. Shallow water, steep waves implies long fetch, weíre talking lee shore, no one should stay anchored in such a situation.

There is now a theory on the table that ďscopeĒ means chain thatís lying on the ground. So Iím leaving that discussion behind. Letís discuss how a snubber reduces load on the rode.

I suppose when the chain is a straight line between anchor and bow roller, then the spring in a snubber would offer protection, but letís be fair, how many times would any sailor allow that condition to occur? Any catenary, no matter how small, offers protection/cushion.

In 5 metres of water at 5:1 scope, the chain I have out weighs 70-odd pounds, much more, I suspect than the average kellet that is deemed to provide adequate catenary.

The snubber would also need to have at least the same tensile strength as the chain otherwise it represents a weak link. Thatís a big piece of rope in a 10mm all-chain rode.

If there is rope in the rode (not Dyneema) the rope cushions the load and no snubber required.

Finally, given that the majority of sailors anchor anchor on 5:1 scope (at least they do where I sail), boats anchoring on 10:1 scope cause a lot of angst as their swing circle in a busy anchorage will cause all kinds of problems when the wind shifts.
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