How Chain Size Impacts the Catenary

[craigsmith]

Originally Posted by lancelot9898

After thinking about the arguments some more and considering how the catenary effect is "gone" under storm conditions as the anchor rode is almost straight, I think that chain weight remains an important component since the force exerted by the chain while being less than the force loading upon the boat it remains significant.

No. If the catenary effect is "gone" then the weight of the chain is clearly by definition no longer significant. It is only significant so long as it is serving to reduce the vertical loading on the anchor. If the chain's straight, it's not doing much is it? You don't even need to do the numbers, it's simple common sense. QED.

Originally Posted by lancelot9898

Plus the dynamic loading is probably the critical situation causing anchor break out and again the chain weight will be an important contibutor as the boat surges back and forth. Appreciate your calculations.

No. If the catenary effect is "gone" then it can't possibly be "an important contributor", huh.

The only effective means of dampening dynamic loading is by way of dedicated snubber / rope.

Fishwife is spot on.

[lancelot9898]

Originally Posted by craigsmith

No. If the catenary effect is "gone" then the weight of the chain is clearly by definition no longer significant. It is only significant so long as it is serving to reduce the vertical loading on the anchor. If the chain's straight, it's not doing much is it? You don't even need to do the numbers, it's simple common sense. QED.


No. If the catenary effect is "gone" then it can't possibly be "an important contributor", huh.

The only effective means of dampening dynamic loading is by way of dedicated snubber / rope.

Fishwife is spot on.

Do a force diagram on the boat with and without chain under severe conditions! And unless we exist with zero gravity here on earth I think you'll find your assumptions wrong.

[fishwife]

I'd agree that the weight of the chain, even when the catenary has 'disappeared' exerts a component of vertical force into the equation, however, in practical applications I fail to see the relevance. Weight of chain does have a part to play in resistance to horizontal force but when the horizontal force overcomes the other elements, what matters is the ability of the anchor points (anchor and bow) to resist the combined forces. The theory is all well and good but the practice comes down to how likely you are to drag or even loose all purchase on the bottom. I know from practical experience in several storms that scope is king, be it chain, rope or a combination.

P.

[estarzinger]

I swear to myself I will stay away from anchoring threads, and then can't control myself.

Four points on chain that don't seem to have been made:

#1. Often in strong winds, the load on the rode is not steady - the wind is gusting and the boat is swinging. In this case, the weight of the chain is helpful to give the anchor an opportunity to set/rest in the low points of the cyclic loading - when the load decreases the chain lowers the angle of pull on the anchor (compared to rope) and allows it to dig more deeply. With rope the angle will often stay high and not give the same opportunity for the anchor to get more settled.

#2 When the boat is swings back and forth, as most modern boats do quite a bit, the friction of the chain on the bottom is quite high and damps down all the shock loads.

#3 In rocks, I have often dove on my anchor rodes in quite strong winds and found the chain snaked thru and under the rocks making a horizontal pull on the anchor. While with rope, the rope almost always 'floats' up and free of the rocks and is directly pulling with a vertical component on the anchor.

These are all direct personal observation from frequently diving on my gear. I don't really care what the theoritical models say, because if they don't include these points they are not accurately modelling the real world.

#4 All this is pretty irrelevant to the reason to use chain, which is that long term it is a ton more reliable than rope.

And no, I really don't want to debate any of this with Craig, who has developed an amazingly unpleasant style for a Kiwi.

[MarkJ]

Originally Posted by donradcliffe

anchor including the dynamic effects of wind, waves, sailing at the anchor, damping from movement of the chain through the water, stretch in a snubber, etc.?'

One of the things I look at is the fetch and liklihood of waves.
Pulling neatly back on a stright bit of chain seems fine. Then you cop one wave and whammo!

[colemj]

Originally Posted by estarzinger

I swear to myself I will stay away from anchoring threads, and then can't control myself.

Four points on chain that don't seem to have been made:

#1. Often in strong winds, the load on the rode is not steady - the wind is gusting and the boat is swinging. In this case, the weight of the chain is helpful to give the anchor an opportunity to set/rest in the low points of the cyclic loading - when the load decreases the chain lowers the angle of pull on the anchor (compared to rope) and allows it to dig more deeply. With rope the angle will often stay high and not give the same opportunity for the anchor to get more settled.

#2 When the boat is swings back and forth, as most modern boats do quite a bit, the friction of the chain on the bottom is quite high and damps down all the shock loads.

#3 In rocks, I have often dove on my anchor rodes in quite strong winds and found the chain snaked thru and under the rocks making a horizontal pull on the anchor. While with rope, the rope almost always 'floats' up and free of the rocks and is directly pulling with a vertical component on the anchor.

These are all direct personal observation from frequently diving on my gear. I don't really care what the theoritical models say, because if they don't include these points they are not accurately modelling the real world.

#4 All this is pretty irrelevant to the reason to use chain, which is that long term it is a ton more reliable than rope.

And no, I really don't want to debate any of this with Craig, who has developed an amazingly unpleasant style for a Kiwi.

I don't think anyone was advocating all rope, but a combination rode. And the specific debate was whether the greater initial static cantenary of chain was useful to the holding power of the anchor system. Not about the usefulness of chain for all other aspects of anchoring.

Your first point addresses the debate somewhat, but don't you think the "rest" the anchor experiences that is afforded by the weight of the chain would be similar to that afforded by the elasticity of nylon mitigating the force on the anchor? Also, if the pull on the rode declines so that the chain resumes a good cantanery, I doubt there would be enough pull on the already well-set anchor to cause it to bury further.

Most of your points would be addressed by a combination rode also, as no one would suggest that it is a good idea to not have a chain portion where the rode lies along the bottom.

I'm curious about point #3. When the chain is snaked through and around rocks, do you think that there is really any pull on the anchor at all? I've had our chain 90* around a coral head once and there wasn't any force getting back to the anchor (I dove and watched).

My experiences have been different than yours on point #4. On our combination rode, the chain always wore out before the rope. I could agree with your statement if you changed the word "reliable" to "convenient" (the reason we now have all chain).

Mark

[estarzinger]

Originally Posted by colemj

the specific debate was whether the greater initial static cantenary

I thought my first three points all had some relevance to chain catenary (compared to rope) - but yes in a dynamic and not static situation. The world is after all a dynamic place.

Most of your points would be addressed by a combination rode also,

YEs, agreed. Almost all of us, who use a snubber on all chain, are actually using a 'combination rode'. So in actual practice this debate has long been solved and agreed by cruisers.

The only debate is the proportion of rope vs chain in the combination, but even in that, out in the cruising fleet there is a pretty decent consensus that of the rode that actually is usually put out (as opposed to the rode that usually sits in the locker), most of it should be chain.

I know there are a few mavericks who use more rope, and with a multihull you may be one of them, but if you look around the anchorage in say Ushuaia or Bora Bora you will not see all that wide a variation.

I could agree with your statement if you changed the word "reliable" to "convenient" (the reason we now have all chain).

I know what you mean about convenient and agree on chain's attractiveness on that, but no reliable is what I meant. Rope is very very vulnerable to chafe in storms. If you look at moorings, where that is much greater experience, the failure mode is the rope chafes or the shackles and swivels break (or the pins come out). Putting chafe aside, get rope anywhere near coral and you have an instant failure, and the same can be said if you anchor in harbours where they is any metal junk on the bottom. Putting being cut on the bottom aside, when I look at where the rope runs over my gypsy it is clearly being degraded while the chain is not.

So, my experience is that chain is way more reliable out in the real world. I have sure had rope chafe and cut, but have never actualy broken any chain. All I have ever done is regalvinaze it. Have you ever actually broken any chain?

[Bash]

Originally Posted by hummingway

Given a situation where a tide is going to turn you around 180 degrees in the course of a night it would seem to me that catenary has a role to play in anchoring.

Despite the one-word dismissal by the resident anchor salesman, I would chime in that my own experience at anchor supports hummingway's observation. We have semi-diurnal tides in SF Bay, and it's a rare evening where I don't go through a complete tidal shift because it only takes six hours to go from high to low. Weighing anchor in this situation often involves having the windlass spin the boat around because the anchor is actually sitting astern of the boat, still in the original position and orientation where it was set. What has happened is that the wind and tides have not provided sufficient force to move the chain.

To state, dismissively, that catenary has nothing to do with this is somewhat naive.

[noelex 77]

Originally Posted by estarzinger

#3 In rocks, I have often dove on my anchor rodes in quite strong winds and found the chain snaked thru and under the rocks making a horizontal pull on the anchor. While with rope, the rope almost always 'floats' up and free of the rocks and is directly pulling with a vertical component on the anchor.

.

I have noted this on several occasions myself.
Just yesterday my wife jumped in for a swim and to check the depth of some rocks within our swinging circle. She swam over to the anchor to watch it set. (worth doing if you are interested in how anchors work)
Anyway it did not set or move at all. The chain had caught around some rocks and this was taking all the reverse pull. A quick motor forward released the chain and the anchor set normally.
Its not common and the chain often releases with a small change in wind direction, but this is lesson to those that believe a reverse pull guarantees the holding power of the anchor.
Use an anchor that sets reliably and an anchor alarm as back up.

I do agree with the posts that suggest all chain rode for cruising boats, as others have pointed out it has a lot of benefits, but I do no believe any significant increase in holding power is one of these advantages.

.

[Hiracer]

As a matter of physics, weight helps chain catenary. But I agree with Craig that catenary is not very important.

Catenary as a substitute for a snubber is a false path because in conditions where you need it most, there is no catenary for all practical purposes. So never swap out your snubber for catenary.

Catenary to reduce vertical force vectors at the anchor fails to appreciate the overwhelming role that scope plays, especially in high winds.

Catenary can help for some of the reasons stated in this thread, but in each case the weight dedicated to a heavier chain would have been better served by using a longer chain of normal weight.

Again, this is because catenary functionally disappears when you need it most, and scope becomes significantly more important. So put your chain weight into length, not thickness. All of us can only carry so much chain weight. Between thickness and length, length is by far the more useful of the two, once thickness reaches the minimum needed for the job.

[gvolos]

I used to skipper on a Little Harbor 62. The boat arrived in Europe with 70 meters of 10mm chain and a 75lb CQR primary anchor. What a joke!! After dragging all over the place here in the windy Aegean, I convinced the owner to change everything. New Delta (can't remember the weight but larger then the CQR), new 120 meters of 12 mm chain, and new 2500w Lofran. That was the end of my worries. I don't know if it was the anchor, the scope or the chain size, but it's definitely the worst thing anyone can skimp on.
Just my two cents.

[rebel heart]

Originally Posted by SvenG

Why is it that every single anchoring thread on CF has to be about the soft bottom Rocna miracle anchor ?

Is there really no other aspect of anchoring anywhere that is worth discussing ?

Wow.



-Sven

I feel your pain. Craig even went onto my blog and criticized me for putting my family at risk for not using a Rocna anchor (over a Manson Supreme).

Rebel Heart - Sailing, cruising, liveaboard blog and website - Eric's Blog - our new manson supreme*anchor

I'm sure this post will get deleted, while Craig will continue to bash everyone who doesn't completely subscribe to his line of thinking. Somehow, Rocna Inc. has become the all seeing and unfailing eye of anchoring.

[bene505]

I've always marvelled at the "3:1 for chain, 7:1 for line" discussions.

For instance, what happens when al your chain is out and then you let out 10 feet of line that's attached at the end of your chain. By the 7:1 rules you are now worse off than if you reeled the line back in. Hogwash.

For a limited weight (and $) money budget, it's best to have some good chain that meets your needs and then back that up with a ton of line to provide great scope (and shock absorption) when the weather gets really nasty. And focus on chafe prevention.

At least from my little experience, that's what I think. But then I always seem to be over hard sand in 10 feet of water.

Regards,
Brad

[MarkJ]

Originally Posted by bene505

. But then I always seem to be over hard sand in 10 feet of water.

Regards,
Brad

Luxury. I havent anchored in 10 feet over sand for more than 12 months.

Tonight it is 13 meters (42 feet) over muck. thats about the norm....
I had 40 meters out and came too close to another boat they have 50 out, so I went down to 50.
no one much seems to like that 3:1 they all going more.

As for 'Garbage in: Garbage out' comments. He ain't gunna sell much insulting potential customers

[sailorboy1]

I find it interesting that if you click the link on CF to Mason Surpreme and then click the sizing tab, that it starts by talking about how critical the chain is and when in doubt to size the chain higher. Seems in lots of ways the opposite to what their competitor is saying here on CF.

And lets be fair; not everything Craig says is wrong! It's just that we don't necessary believe everything he says is right. Do your our research and make your own decision based on it and I would bet you end up with as good an answer as anyone else, just different.