Chain Versus Rope Scope ?

[s/v Jedi]

Originally Posted by cfarrar

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.

Very good photo. It also shows a Maxwell chain stopper. Get one.

cheers,
Nick.

[wsmurdoch]

I've enjoyed working my way through this site.

Tuning an Anchor Rode

Bill

[avb3]

Originally Posted by wsmurdoch

I've enjoyed working my way through this site.

Tuning an Anchor Rode

Bill

Thanks for that link. I suspect some "traditionalists" with lot of experience will disagree with many of the conclusions therein, but it seems to be made from a scientific point of view.

Bookmarked for sure!

[s/v Jedi]

It's a shame I wrote this in Dutch but some can read it while Google translate will come up with some funny but little accurate translations; this is from 2006 after our hurricane adventures:

Part 1 - the gear http://www.sv-jedi.org/sv_jedi/2006/...er_uitrus.html

Part 2 - the method http://www.sv-jedi.org/sv_jedi/2006/..._anker_me.html

It's a bit funny too, except when you're French...

ciao!
Nick.

[jewel114]

Her's my take. Double the length of the boat in chain (for bottom abrasion) and then 3 strand nylon. If you look at the breaking strength of each part of the system, shackles etc, you'll have a surprise. Weakest link in a chain kinda thing.
If you watch your rode at a rough anghorage it tightens and loosens when you have enough scope (7:1)min. If you swing too much because of a tight anchorage, set up a Bahamian Moor rather than sacrifice scope.
Read tests by anchor manufacturers, tells most.

[s/v Jedi]

Originally Posted by jewel114

Her's my take. Double the length of the boat in chain (for bottom abrasion) and then 3 strand nylon. If you look at the breaking strength of each part of the system, shackles etc, you'll have a surprise. Weakest link in a chain kinda thing.
If you watch your rode at a rough anghorage it tightens and loosens when you have enough scope (7:1)min. If you swing too much because of a tight anchorage, set up a Bahamian Moor rather than sacrifice scope.
Read tests by anchor manufacturers, tells most.

7:1 wt-frak, that is way too much. I might do that in a hurricane. Anchor gear must work 100% at 5:1 scope. If you drag with that, you need a bigger or better anchor, or both.

What is your reason for the nylon?

cheers,
Nick.

[Mike OReilly]

Originally Posted by s/v Jedi

7:1 wt-frak, that is way too much. I might do that in a hurricane. Anchor gear must work 100% at 5:1 scope. If you drag with that, you need a bigger or better anchor, or both.

CYA (Canadian Yachting Association) standard that is taught:

3:1 for lunch stop
5:1 standard overnight
7:1 storm (or leaving boat for long time)

Same for ASA/RYA and others?

Nylon snubbers for sure.

Seems to me going with a fixed chain/nylon rode (like double LOA for chain) will only be perfect for a specific range of anchoring conditions. That would be fine if your anchoring is limited to this range, but not so otherwise.

[avb3]

Originally Posted by s/v Jedi

7:1 wt-frak, that is way too much. I might do that in a hurricane. Anchor gear must work 100% at 5:1 scope. If you drag with that, you need a bigger or better anchor, or both.

What is your reason for the nylon?

cheers,
Nick.

Perhaps the same reason this conclusion was reached? Go towards bottom of page, point 6, Conclusions.

[sabray]

Why use 3 strand? Octoplait or similar are so much better, they store better have good anchor rhode stats. I still have some 3 strand as secondary because it's money but no reason to buy 3 strand new. For anchor rhode buy some plaited line.

[delmarrey]

Originally Posted by sabray

Why use 3 strand? Octoplait or similar are so much better, they store better have good anchor rhode stats. I still have some 3 strand as secondary because it's money but no reason to buy 3 strand new. For anchor rhode buy some plaited line.

What I hate about 3 strand is it will try to untwist under load, which is when I'm weighing anchor, twisting the chain too.

[jeremiason]

We have been fulltime cruisers for about 16 months. During that time we have been on the hook about 60% of the time and so far haven't dragged (Thank you sea gods).

We use all chain rode with a Rocna 55lbs anchor and a 5/8" 12 foot long nylon snubber on our Catalina 47. We routinely anchor at 5 to 1 scope and let out chain in the event of rough seas or heavy winds.

Over the summer, we were in the Sea of Cortez and expereinced two extreme winds events while at anchor. The first was a "Chubasco", which hit us with 55 knot winds for about 20 minutes and then continued for another 2.5 hours at 40 knots. We also expereicened an Elephante, which blew at 40 knots for 13 hours. We have also been on the hook during a number of 25 knot plus blows for extended periods.

During one 25 knot blow along Baja California, I dove the anchor to make sure it was holding ok... What I found was pretty shocking. At the time I was anchored in 30 feet of water with 175 feet of chain out.

I swam from the bow and followed the rode, after about 75 feet, the chain took a 90 degree turn in the sand and ran to the anchor. In other words, my 37,000 lbs. boat was riding along in 25 knots of wind, using the weight of the chain only. So regardless of what the experts say, at least in this instance the weight of the chain did help.

Look the fact is, chain lasts longer, won't caffe, provides more weight for cantanary and with a proper windless is easier to handle...

In my humble opinion, if your boat can handle the weight... Chain is the way to go.

[Dockhead]

Originally Posted by Jim Cate

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

Well, yes. I think this is why my primary rode is all chain.

I think most of us were responding to the myth that chain increases ultimate holding power due to catenary. In ultimate conditions I think that, contrary to what this myth says, it's clear that rope is actually better than chain, but for the issue of chafe.

Rope has a lot of other advantages too. But like you, I use chain, nearly half a ton of it

[conachair]

[QUOTE=delmarrey;854912

So with that, one needs enough chain to keep the boat from lifting the shank, and that's where scope comes in. The harder the blow the more scope, and then maybe a killet or two.[/QUOTE]

Except that isn't the case.

Synthesis

Takes less of a blow than you think to lift the chain off the seabed, even with extra weight. Any keen snorklers here to confirm that?

[Dockhead]

Originally Posted by jeremiason

During one 25 knot blow along Baja California, I dove the anchor to make sure it was holding ok... What I found was pretty shocking. At the time I was anchored in 30 feet of water with 175 feet of chain out.

I swam from the bow and followed the rode, after about 75 feet, the chain took a 90 degree turn in the sand and ran to the anchor. In other words, my 37,000 lbs. boat was riding along in 25 knots of wind, using the weight of the chain only. So regardless of what the experts say, at least in this instance the weight of the chain did help.

I think you might consider conducting a review of your anchor setting procedures!!

[Dockhead]

Originally Posted by conachair

Except that isn't the case.

Synthesis

Takes less of a blow than you think to lift the chain off the seabed, even with extra weight. Any keen snorklers here to confirm that?

Exactly right. I think that was Dashew's main point -- the ability of the weight of chain to keep the shank down diminishes with increasing load -- exactly the opposite of what you want. At some point it disappears, when the chain goes bar-tight.

I have had 330 feet of 1/2" chain bar tight, weighing nearly half a ton, so it's not only survival storms where this happens!! This happened to me in a moderate gale, about 30 knots of wind. The 121 pound Rocna didn't budge an inch, but the snubber parted during the night!

The point of scope is not to have a greater weight of chain out, but to change the geometry between your bow and the anchor. The longer the rode, the shallower the angle, for a given water depth. Dashew's point was that this effect -- the real purpose of scope -- is the same whether you have heavy chain, light chain, rope, or whatever.