Chain vs rope scope question

[Neil Gordon]

Currently I anchor with 30' of 3/8" chain and 1/2" rope thereafter. I'm not likely to go all chain, but I am thinking of adding an additional 30'. I typically anchor in 20' of (high tide) water. How much less scope might I put out if I double the chain length?

[kerrydeare]

Currently I anchor with 30' of 3/8" chain and 1/2" rope thereafter. I'm not likely to go all chain, but I am thinking of adding an additional 30'. I typically anchor in 20' of (high tide) water. How much less scope might I put out if I double the chain length?

For me. this is a "how long is a piece of string" question, Neil. Not to be facetious about it, but the issues hinge on your particular type and size of anchor, technique, conditions (including the bottom, etc.), the anchorage situation, etc. I know that you are well aware of all this, but just thought it worth mentioning.

In your specific case, I had the same boat and a similar (I think) anchoring rig for a long time. I routinely used 60 feet or slightly more of chain (in my case 5/16 and not 3/8) fitted with 300 feet of New England 9/16 rope on the genuine CQR 35. In a wide range of conditions over time, I cannot say for sure that the 60 feet or so of chain, together with the 25 or 50 or more feet of rope, ever pulled the chain completely off the bottom. I suspect I would have been able to identify that situation but I don't ever recall doing so. I am not talking about hurricanne winds, but Force 9 or 10 happened several times over the years. We also routinely carried but rarely deployed 2 Danforth 20H anchors, plus a Fortress, etc., etc, each with its own chain and rode. Most often it was just too complicated (and even dangerous) to set up more complicated anchor schemes while single-handing. I don't know how all that got stuffed into such a little boat, but it did. In all cases I let out all the chain and began to set the anchor by backing to pull the chain straight, and then I let out rode based on conditions. We'd then hammer the whole thing by backing down at high revs to make sure.

Over a very long period of time, I cannot recall dragging that rig (but I am sure it must have happened). I never fitted a windlass but instead used one of those plastic milk crates (with some sort of non-skid on the bottom) to handle the chain. If it seemed reasonable, I simply flaked the chain into the crate until the next anchorage. Often the crate itself was secured with small stuff,and just as often the entire chain was fed to the locker, depending, etc. The "windlass" consisted of several pairs of sturdy work gloves with plastic snap hooks attached so they could hang on the lifelines and dry.

I hope this gives a few ideas that may be useful. Of course all internet sailing discussions eventually become questions about anchors or Hitler, but let's just skip that part for now. And please ignore my pedantics.

Armond

[fmueller]

Neil,

I’m no expert but I don’t think the catenary effect of the weight of chain changes the suggested scope you should have out much or at all for boats of our displacement. In high wind and current even an all chain road will be essentially straight line bow to anchor.

Catenary does become effective for much larger ships because mass (of the chain) increases cubically by volume - while load (wind and water on the hull surface mostly) increases arithmetically the by the square of surface. That’s why you often see an anchored tanker and the anchor chain will just drop nearly vertically out of the hawspipe.

Chain prevents wear against rock and especially coral. Someone more experienced will comment, but some chain helps with initial bite and set. I’ve read 30 ft is generally enough for that effect.

One other thought is that a significant length of nylon offers shock absorbing to the rig and that is no small thing in keeping the anchor from yanking free after initial set. That’s why snubbers are used on all chain rigs.

Cheers

[Neil Gordon]

>>For me. this is a "how long is a piece of string" question, Neil. <<

The string part totals around 300', but that's not my question.

>>... type and size of anchor, technique, conditions (including the bottom, etc.), the anchorage situation, etc.<<

22 lb. Lewmar Claw on the roller. Typical bottom is mud or sand. Typical situation is I'm surrounded by boats with all chain... I figure if I double my chain to 60', I'd be closer to all chain than I am now... and might be able to swing in a smaller circle, more like my neighbors.

I know that you are well aware of all this, but just thought it worth mentioning.

In your specific case, I had the same boat and a similar (I think) anchoring rig for a long time. I routinely used 60 feet or slightly more of chain (in my case 5/16 and not 3/8) fitted with 300 feet of New England 9/16 rope on the genuine CQR 35. We also routinely carried but rarely deployed 2 Danforth 20H andchors, plus a Fortress, etc., etc, each with its own chain and rode. I don't know how all that got stuffed into such a little boat, but it did.

>> The "windlass" consisted of several pairs of sturdy work gloves with plastic snap hooks attached so they could hang on the lifelines and dry.<<

I use a human windlass, too. Easiest is if there's some bounce in the bow... hold when it goes up, pull when it goes down. At most, I'm pulling 20' of chain + anchor, most of which is in the water. Doubling the chain length won't change the weight of what I'm lifting, although I'll be dong it for longer.

>>Of course all internet sailing discussions eventually become questions about ...<<

Wheels v tillers, locked v unlocked props, and more.

[Steve Laume]

Raven runs 90' of 5/16" chain with another 200' of 5/8" nylon spliced to it. I like to anchor as shallow as I can and almost always put out all the chain and some nylon. This gives me at least 5 to one in most cases. I also have about a 30' length of 1/2" nylon with a locking chain hook on the end. My usual method is to let out almost all of the chain, then hook the snubber to it and let out enough nylon to catch up on the snubber. The snubber is already run through the Stbd chock. Once it takes a load I take the anchor rode through the port chock and cleat it off so that I have created a bridle. Having a snubber and the rode connecting the boat to the chain makes me feel good. 3/8" chain is heavy and much stronger than it needs to be. I went with 5/16" at about 1# per foot and got a pail from Defender. I have had a couple of incidents where nylon may very well have chafed though. Chain helps you sleep well, Steve.

https://www.defender.com/product.jsp?na ... &id=325302

[fmueller]

Neil,

Here’s a good write up on catenary effect on the Rocna site. That is the heart of your question.

http://kb.rocna.com/kb/Scope_vs_catenary

[Steve Laume]

Whenever I am preparing to anchor in a crowded spot, I try to talk to those around me. I want to know what kind of anchor they are on and more importantly, how much scope they have out. If they are on 3 to 1 and I put out 7 to 1 there could be problems in a wind shift. It also lets me know if they ahve clew about what they are doing.

There have been many times where Raven swings around on her chain with not pull on the anchor at all, Steve.

[wikakaru]

Hi Neil,

I cruised for over 7 years on several different boats. One was a 22,000 lb steel cutter equipped with a 30 kg (66 lb) Bruce anchor, the other was a 14,000 lb cutter equipped with a 20 kg (44 lb) Vulcan anchor. I found on both of these boats, day after day, in good weather and foul, that I almost never used more than 3:1 scope with all chain and virtually never dragged anchor. The only exceptions were a couple of places in the Caribbean with thin (as in an inch or two) sand over featureless limestone, where there was just nothing for the anchor to dig into, and a few places with very thin (as in not viscous) mud, where a larger surface area anchor like a Fortress would have been more effective.

As I later moved to smaller boats that didn't have windlasses, I had to move from all-chain to chain/nylon combination. My solution was to equip the boat with enough chain for 3:1 scope in the kind of places I typically anchored, and have the rest nylon. When I anchored I would put out all the chain, which gave me 3:1 scope, plus about 15 feet of nylon to act as a snubber. If for some reason I had to anchor in an unusually deep anchorage I would use additional rode as appropriate. I think this is the best compromise for most situations short of world cruising, when I would opt for all chain and a windlass to handle it.

If you don't have excellent holding when backing down on your anchor (zero movement at full RPM in reverse gear) with 3:1 scope in at least 95% of the places you anchor, then there is a problem with your choice of anchor or your anchoring technique. I had 3-bladed props on both of my big cruising boats, and I found that if the anchor didn't move in full reverse with that kind of pull, it wasn't going to move in any weather short of a hurricane.

I suggest that, since you typically anchor in 20 feet of water at high tide, you should have 60 feet of chain. Try that with your current anchor, and (assuming you have good anchoring technique) if you don't stay stuck at full RPM in reverse with that setup, upgrade your anchor next.

Smooth sailing,

--Jim

[kerrydeare]

... 22 lb. Lewmar Claw on the roller. Typical bottom is mud or sand. Typical situation is I'm surrounded by boats with all chain... I figure if I double my chain to 60', I'd be closer to all chain than I am now... and might be able to swing in a smaller circle ...

First of all, hats off to Jim's comments directly above. The fact that we fully agree is merely coincidence (lame humor).

For me that 22 pound anchor would be light, but of course "it depends." After I responded I was again thinking about what actually happened over time, and I am pretty sure I had to use the engine to dislodge the anchor many many times, it was set so well. Not particularly convenient, but safe.

Regarding crowded conditions, I suspect where you commonly sail the harbors are usually crowded and sometimes filled with enthusiastic "amateurs" (no disrespect intended). That unfortunately gives you fewer options, but I'd venture to say that doubling the chain will give you a much better set of choices even though you may at times not quite meet the so-called experts suggestions on scope. BTW and again I know you know, don't forget to add 5 feet to the 20 foot depth. Then if you go 7 to 1 you are somewhere in southern New Hampshire.

Another thing that happened all too often was that, despite being an early arrival at the anchorage, I ended up moving for safety just because it was easier than messing with possibly armed Merkins (yeah, I know about no politics here, but then an old guy sometimes just needs a break).

[kerrydeare]

... I try to talk to those around me. I want to know what kind of anchor they are on and more importantly, how much scope they have out ... lets me know if they [know] what they are doing ...

Steve, chatting folks up never hurts. This is not to mention that it often results in free scotch (not necessarily single malt). Would that the planet worked this way.

[Neil Gordon]

For me that 22 pound anchor would be light, but of course "it depends."

it sets easily, holds when I back down hard, and resets when the wind/current changes. It also trips easily once the chain is straight up and down. Is there anything else it's supposed to do?

I also have a 22 lb. Danforth.

Oh, and also a quite cute 15 lb. CQR, in the basement, which the prior owner used as a primary, although I'm not sure they ever anchored other than for lunch. I don't tend to stop just for lunch, but if I do, I'd just as soon set my primary.

[kerrydeare]

... it sets easily, holds when I back down hard, and resets when the wind/current changes. It also trips easily once the chain is straight up and down. Is there anything else it's supposed to do? ...

If I knew the answer I guess I'd be a famous sailing author (which I'm not). I guess I always go with "bigger is better."

For a while I sailed with a couple in the Bahama Islands who had a boat in the 40 range that was quite nice. He used to call his CQR 65 on all chain a "portable mooring" and admitted that it was a handful at times. Even so, none of us minded rafting on his boat and getting a sound night's sleep.

[wikakaru]

For me that 22 pound anchor would be light, but of course "it depends."

it sets easily, holds when I back down hard, and resets when the wind/current changes. It also trips easily once the chain is straight up and down. Is there anything else it's supposed to do?

I also have a 22 lb. Danforth.

Oh, and also a quite cute 15 lb. CQR, in the basement, which the prior owner used as a primary, although I'm not sure they ever anchored other than for lunch. I don't tend to stop just for lunch, but if I do, I'd just as soon set my primary.

That's about all you can ask for in an anchor. I think 22 lbs. is a reasonable size for coastal cruising for a CD28. My very rough and very conservative rule of thumb for sizing a Bruce anchor is about 3 pounds of anchor for every 1,000 pounds of displacement, or 27 lbs. for your 9,000 lb. CD28. Of course, they don't make anchors that size. According to Bruce's sizing guide, the 22 lb. anchor is considered a "storm anchor" for 29-32 foot boats, so they think you have a bit more anchor than you need. The bottom line is how it performs for you, and if you have good results when backing down hard against the anchor, there's no reason to change.
http://2.bp.blogspot.com/-nrRel8XGPw8/T ... Anchor.jpg

With the Danforth you have a pretty good mud anchor (though you will have to watch for wind/current shifts).

The basement is a nice place to keep that "cute" 15 lb. CQR.

Smooth sailing (and anchoring),

--Jim

[kerrydeare]

... With the Danforth you have a pretty good mud anchor (though you will have to watch for wind/current shifts) ...

Not to get too far off Neil's subject (I think we have enough time Covidly speaking), I've often thought the Danforth or "Ogg" anchor really gets a worse rep these days than necessary. This is the anchor that "won" the Normandy invasion by pulling those landing craft off the beach when the time came (I defer to the military types among us who have acquaintance with such issues).

Speaking strictly of the older "high tensile" models (i.e., the genuine high tensile that may no longer even be manufactured), I've owned and still have a basement full of the Danforths: the 5H (dinghy), the 12H, the 20H, and, prize of prizes, the 35H. Long ago I set my CD28 on the 5H and found that while it was quite small, just about any wind would set the little thing so deep that getting it out became an issue.

I only had a single 5H for the dinghy, but the 12's and 20's were always rigged in pairs and so set, usually in a tide stream. When the tide turned they didn't have to re-set, and they performed very well. I once laid in Hurricane Gloria (1985) on a pair of 20H on long chain and very long rode and even though it required a dive mask to go forward and check the gear, these anchors never failed. I never did find conditions that required the 35H, but then I only had a small boat. The 35H would be a real "monster" on the foredeck, even though 35 pounds is not all that heavy.

Just making a pitch for these classics (which of course are for sale to a good home).

[jbenagh]

Neil,
in anticipation of heading to Maine this summer, I bought 130* feet of chain this winter. I used to have 30 feet of chain and then 1/2 in nylon rode. What we found last few times in Penobscot Bay and further east, we were the only boat on rope and let out a lot more scope than other boats which was a problem when we pulled into an anchorage at 5-6pm (afternoon is the best sailing winds there). So far, in the first ~10 days in Casco Bay we've typically anchored (in very settled weather) on 3:1 with a 1/2 in pennant on a chain hook, the chain drops straight down and we are very compact. There are more boats with nylon in Casco Bay than further east I think.
*Why 130 feet? Two reasons. The old chain was 30 feet so I can keep my old rode markers and just remember they are 100 feet bigger than they say. Also most places we anchor are right around 30 feet at high tide (including bow height) so at 5:1, we'd be just barely on the rode and wouldn't use the chain hook. Oh and a 3rd reason is that 130 feet of 5/16 BBB is about 150lbs and the boat sailed fine with my kids in the v berth when they weighed about that much so I figured it wouldn't hurt the performance much.
I don't have a windlass (yet) and it it more work to haul up the extra chain but manageable. In 30 foot depth I'm hauling the same weight at a time as I was before. You really do notice when the 35lb CQR adds to the chain weight. I made a 1/2 in PVC stick to rearrange the chain pile in the rode compartment, otherwise the chain cones way too early.
I thought I might offload the chain except when cruising but it's quite a project to coordinate the tide at the dock so I think I'll leave it.
Jeff