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Old 07-01-2012, 13:08   #16
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Re: Chain versus rope scope?

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Originally Posted by s/v Jedi View Post
Sure, but without the weight, you would rip it apart. Fluke area and weight go hand in hand. Aluminium isn't suitable for primairy anchors so I leave that out.

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That's odd b/c the aluminum Fortress claims to be the best. Fortress Anchors - Myths and Facts
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Old 07-01-2012, 13:13   #17
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Quote:
Originally Posted by delmarrey

That's odd b/c the aluminum Fortress claims to be the best. Fortress Anchors - Myths and Facts
I take it you're not trolling me? If you would have come up with an aluminium Spade as primary, I could have believed it, but a Fortress?! As primairy?!

If there is one thing you should do, it is forget that idea. Please...

cheers,
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Old 07-01-2012, 13:17   #18
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Re: Chain versus rope scope?

Rather than discuss which anchor is best, a topic which we know can spiral into a chasm we will never get out of, let's assume you are really, really happy with YOUR primary anchor.

The question remains, chain versus rope and scope and why.

I've had some good answers for me to consider, and I much appreciate them. Besides, I have a pretty good idea which anchor I am interested in, but I leave that for another time.
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Old 07-01-2012, 13:23   #19
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I agree with the thoughts oboutt anchor holding power being more important then chain weight. Under most circumstances the weight of the chain adds to a more stable less sailing around anchored experience. It can lay on the bottom and survive chafe. Killers are great for prestorm anchors. Used to hold the line on the bottom. Otherwise great nuisance. I used one a while it became more a hazard then help.
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Old 07-01-2012, 13:28   #20
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Re: Chain versus rope scope?

I won't argue the point b/c I don't own one but I do machine different grades of aluminum and can tell you some exotic grades wear just as well as some steel anchors might. Fortress Anchors - Testimonials

Although, I prefer the Bruce or Delta's to the sand draggers b/c they'll go as deep as the bottom will allow. Sometimes have trouble getting them up.
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Old 07-01-2012, 13:32   #21
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Re: Chain versus rope scope?

If abrasion was not a possibility then i believe we would all use rope with a high hold anchor.
Scope helps set the anchor with a horizontal pull, ratio to depth ensures same setting angle re-gardless.
Size of anchor is critical in the way of holding power relative to the load the vessel will exert in the conditions allowed for.
What you are trying to do by using a 'rule of thumb' scope is set the anchor to the designers brief, where he considered load, type of ground, ultimate strength etc etc.
Increasing the scope in a blow simply gives you more catenery effect (shock absorption) as correctly mentioned previously.
Cheers Frank
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Old 07-01-2012, 13:37   #22
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pirate Re: Chain versus rope scope?

Reason for all chain...no chafe, excellent damping, makes its own alarm as it transits the bottom... counteracts the outboard hanging of the stern...
Not a weight worrier...
I'm not a round the cans player, just a going somewhere plodder...
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Old 07-01-2012, 13:49   #23
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Re: Chain versus rope scope?

Here in Australia we usually set all chain and most common is a plough anchor, once we have set the anchor i usually pull up a half metre of the chain using 8mm rope with a SS 6 mm round bar bent hook on the end. I cleat this off.
If loads increase due to tide or wind strength the hook bends straight and the boat shudders as the half metre slack suddenly takes up. It certainly wakes everyone on board and has proven its worth many times.
Works for us. Cheers
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Old 07-01-2012, 13:55   #24
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Re: Chain versus rope scope?

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Originally Posted by avb3 View Post
Rather than discuss which anchor is best, a topic which we know can spiral into a chasm we will never get out of, let's assume you are really, really happy with YOUR primary anchor.

The question remains, chain versus rope and scope and why.
But HopCar and Dockhead explained all that in the first couple of posts (in a very complete, nothing to be added to it, way)... and we want to play too

ciao!
Nick.
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Old 07-01-2012, 15:37   #25
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Re: Chain versus rope scope?

Something to consider:

When one is cruising, one spends days, weeks, months at anchor. The vast majority of this time is not in extreme conditions, where the hypothetical "lifting of an all chain rode" into a bar-tight line is an issue. Once you reach that state, the holding power of the anchor is indeed the primary concern, and having a really good hook is all that will keep you in place.

But for the other 99% (?) of the time, the dampening effect of the chain's weight, and the friction of dragging it around on the bottom make one's life much easier and more comfortable on board. The freedom from worry about chafe helps too!

The obsession about ultimate holding in storm conditions seems to drive most of these discussions, and I reckon that there are other factors that should be considered when designing your ground tackle... virtually none of which lead me to a rope rode!

Cheers,

Jim
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Old 07-01-2012, 15:50   #26
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Quote:
Originally Posted by Jim Cate
The obsession about ultimate holding in storm conditions seems to drive most of these discussions, and I reckon that there are other factors that should be considered when designing your ground tackle... virtually none of which lead me to a rope rode!
Agreed. Full chain is the way to go for the primary anchor.

cheers,
Nick.
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Old 07-01-2012, 15:51   #27
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Re: Chain versus rope scope?

We all agree that if chafe is an issue, chain is the only way to go but someone needs to put to rest this notion that chain increases ultimate holding power when using proper scope. Calculations and reports from people (myself included) who have witnessed chains that are straight as an arrow hasn't done it. I challenge someone to do a whole bunch of pull tests with the exact same anchor on the same bottom with reasonable scope (say 6:1) using an all chain rode and a combination rode (where's Maine Sail?). I am positive that there will be no statistically significant difference. In real world conditions where there are dynamics involved, a well tuned combination rode will actually have the lowest loads on the anchor due to the stretch in the line. I think that it is worth noting that fortress, the undisputed highest holding power anchors, recommends a very short chain leader (6-12') only instead of all chain.

It is true that in calm weather, chain will keep your swing circle down. It is also true that in extremely deep water, chain does start to have catenary but this is a very unusual place for one of our boats to be anchored. Of course you can get catenary with short lengths of rode as well if you use heavy enough chain but it would be ridiculously heavy and impractical to carry around.

For all of this arguing that chain does not increase holding power, I prefer an all chain primary rode with a snubber. I prefer this because of chafe and how the chain reacts in the very lightly loaded conditions that it is normally in. Since the advantage of chain is the abrasion resistance, I prefer smaller diameter high tensile to deal with all of the weight.

Regarding the original question, the only difference is that without any chain, some anchors will struggle to set at very low scope. Ideally, there would be no upward pull on the anchor (think of it as at least the last link of chain sitting on the bottom if not more). The two ways to do this are to increase scope and to put enough weight in the rode to eliminate any upwards force. If you play around with the numbers of this, you will see that you get the same holding power in a much lighter package by increasing scope slightly and using a combination rode than by using an all chain rode. In situations where the holding power of your anchor will actually be tested, you will be at a scope such that this vertical force is basically negligible. In truth, anchors can tolerate some vertical force without degraded performance which explains why they still do well once set even without any chain at all. In the end, you should basically use the same scope whether it is a mixed rode or all chain unless you want to go to really short scope in calm weather where chain does slightly better.
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Old 07-01-2012, 15:55   #28
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Re: Chain versus rope scope?

Well said...Cheers
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Old 07-01-2012, 15:57   #29
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Re: Chain versus rope scope?

On my previous boat I had 30' of chain and then 3-plait nylon rode. The rode would often slip on the windlass and would get jammed in the hawspipe when I was trying to get the anchor up. Very annoying.

I then went to 30' of chain and 8-plait nylon rode, which is more limp than 3-plait. It did not hang up in the hawspipe but it still slipped on the windlass. Often I had to pull the anchor up by hand.

Now I have 200 feet of chain. It never slips, never hangs up and never chafes. A snubber with a chain hook is a minor expense item. I would never go back to nylon rode.

Plus, as others have noted, more weight on the bottom NEVER hurts. It's better to have the weight in the anchor, but weight in the rode helps in most situations.

I also believe in a second anchor. I have a 75 lb Luke stored in the bilge. If heavy winds are forecast, I'll put that down as well.
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Old 07-01-2012, 16:18   #30
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Re: Chain versus rope scope?

Well said, Klem. I'm not selling anchors, but this photo by Peter Smith shows how catenary disappears under high loads. Clearly chain is for other purposes, as you and others explain so aptly.
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