Recomended anchor chain and rode

[Keith Ingebrigtson]

I have a Catalina 30 and wish to replace my anchor chain and rode. I can't seem to find recommendations on size of chain, length for my boat. I am thinking of 50ft of chain, the chain I have looks like it is 30 years old and I don't trust it. Any recommendations?
Keith
Safari Spirit
Pleasant Harbor, Wa

 

[Capt jgw]

Do you have a windlass? You will not enjoy pulling 50' of chain plus the weight of the anchor by hand. I have 20' of 3/8" chain (bigger than it needs to be, 5/16" would be enough for my 36 footer.) and a 35# anchor and it's about all I can handle. And around here we're often anchoring deep enough to have it all hanging. With a windlass all chain is the way to go, size and type determined by what fits the gypsy. Length determined by depth of water you expect to be anchoring in. (Five to seven times depth, including distance from water to bow roller. I carry 600' total.) All that assuming you will be anchoring often. If you only want it for emergency use, getting the tackle back aboard is less of a concern.

 

[jviss]

Capt. JGW, your ground tackle is indeed extreme! 600' of 3/8" chain, for a 30' boat? I have never heard of such a thing. That's in the neighborhood of 900 lb. of chain.

All chain is great, but few carry more than about 150'. For a chain/rope rode, the conventional thinking is the boat length of chain, then rope. So, 30' of chain, minimum.

 

[Capt jgw]

Actually only 20' chain, the rest 5/8" nylon. That's heavy enough.

 

[David in Sandusky]

I think the "standard" recommendation is a boatlength (30') of chain and the rest nylon. From my experience chartering in the San Juans, I would go for about 200 feet total length which would give you a scope of 7:1 in 25 feet of water at high tide (assuming your bow is 4 feet above the water.) The chain is enough to keep the rode pulling horizontally on the anchor in most protected anchorages. Nylon is a great natural shock absorber. And you avoid putting a large weight of chain in your bow where it will encourage "hobby horsing" in a seaway.

All chain is a necessity where coral could cut a fiber rode. The other advantage is that its 5:1 scope allows boats to lie closer together in a crowded anchorage. But I am not aware of any other advantages to an all chain rode. As noted by the need for a windlass, such a rode is significantly harder to recover than nylon and chain without a windlass.

I am aware of no solid data that shows a five to one chain rode will hold any better than a seven to one nylon and chain rode.

 

[Kings Gambit]

I can't seem to find recommendations on size of chain, length for my boat.

Astonishing.

 

[thinwater]

I am aware of no solid data that shows a five to one chain rode will hold any better than a seven to one nylon and chain rode.

And I don't think you will. The actual scope at the bottom will be similar in storm winds, and unless the chain guy has a long snubber or the water is very deep (>15 feet), the shock loads will be greater. In fact, before windlasses became common place, that much chain rode was very unusual for practical reasons. Now that folks have windlasses, all chain is actually easier to handle than rope, and so the popular choice is all chain.

All chain is nice for reducing swing in moderate weather in tight harbors (in storm winds it's off the bottom and there is not difference). If there are a sharp rock or coral it is something to consider, but 30' will do. Another thing to remember is that a large boat puts a much great cutting force on the rode, a smaller boat much less so, because the load is much lower in relation to the surface area of the rope. Thus, large boats will favor chain for many reasons that do not apply to the OP. Horses for courses, and the big boat answer is not better for the smaller boat.

As for the OP (30' mono), 1/4 G4 (2600-pound WLL) is all the chain the needs, particularly when coupled with 1/2-inch nylon. ABYC only calls for 1400-pound WLL. A modern (Spade/Rocna/ Mantus/Manson Supreme) 25-pound anchor should do fine. The rode tension will never actually exceed about 500 pounds, even in storm winds and some wave action (yes, I do have the data--I have a book on anchoring and rigging coming out in a few months). A Fortress FX-12 or 16 would make a great secondary (depends on the common bottoms types).

BTW, this image is from ABYC H-40 table 1. Actually loads have been measure by several investigators and found to be 3-5 times lower, if a nylon rode or 30-foot snubber is used.

 

[jviss]

All chain is nice for reducing swing in moderate weather in tight harbors (in storm winds it's off the bottom and there is not difference).

Oh, really? 150' of chain, bar-tight and off the bottom in "storm winds," which are - what/ 50kts.? Please substantiate this claim. Sounds ridiculous to me.

 

[Alan Gomes]

Oh, really? 150' of chain, bar-tight and off the bottom in "storm winds," which are - what/ 50kts.? Please substantiate this claim. Sounds ridiculous to me.

Here ya go:
http://kb.rocna.com/kb/Scope_vs_catenary
(See also http://kb.rocna.com/kb/Rode_optimizations#Minimal_practical_chain_lengths)

 

[Meriachee]

Chain reduces swinging swinging. Who knew.

 

[thinwater]

Oh, really? 150' of chain, bar-tight and off the bottom in "storm winds," which are - what/ 50kts.? Please substantiate this claim. Sounds ridiculous to me.

I'm assuming we are anchoring in about 20 feet of water at about 7:1 scope.

Many people have done the math. I have dived in much lighter conditions. Bottom line, it is established fact that at about 40 knots, using G4 chain, the rode will lift off the bottom. For BBB it will take another 5 knots. In shallower water or at lower scope the value is lower. At that point, the scope is still very high, of course, and will exceed 10:1 to over 60 knots. No, the chain does not suddenly become straight and I did not suggest that it did. I did not suggest that holding capacity would suddenly drop. Depending on how much chain is burried with the anchor, yawing may or may not be transmitted to the anchor. The shock absorption capacity of the caternary fades badly at about the same time, but again, does not instantly go to zero.

My point is that by the time the winds reach 50 knots, very little of the chain will be on the bottom, not enough to damp the swing. This is obvious and has been noted by many. There have been studies at large scale that confirm that chain is only the main damping factor in light to moderate conditions. After that, the shape of the boat above and below the water are the main factors.

It may seem ridiculous to you, but consider that the tension on that chain is over 1000 pounds. Imagine pulling that chain with a block and tackle. Can you imagine it staying on the bottom? I cannot. I think this is obvious too.

 

[jviss]

Here ya go:
http://kb.rocna.com/kb/Scope_vs_catenary
(See also http://kb.rocna.com/kb/Rode_optimizations#Minimal_practical_chain_lengths)

It's a computer simulation, and he doesn't provide the code, or the principles of the model. I've seen many bias-confirming models, e.g., most climate change models.

 

[jviss]

It may seem ridiculous to you, but consider that the tension on that chain is over 1000 pounds. Imagine pulling that chain with a block and tackle. Can you imagine it staying on the bottom? I cannot. I think this is obvious too.

If yo look at the Rocna simulation linked by Alan Gomes, you would need not 1,000 lbs. to straighten out the chain, but 4,500 lb. The model shows some catenary left at 720 lb.s pull (320 daN).

So, what is it? 1,000 lbs. pull in a 50 kt blow, or 4,500 lb.? Of course, it depends on your windage, i.e., your boat. How much pull does a 36' sloop generate in 50 kt?

Personal experience; in a 50 kt blow, once, many boats on rope dragged, most on all-chain didn't. Shallow, sand anchorage (Block Island New Harbor).

 

[Apex]

egads....another which anchor is best internet argument....lol. submit your opinion, claim your expertise, subset of facts, puff out your chest. there will be contradicting opinions based on a different variable subset.


to the original poster, perhaps simply stating that recommended anchor & rhode likely wont be found for a specific model, rather generalized recommebdations from anchor mfr and sme (subject matter "experts").
there is some good information posted in here despite penile comparison arguments. good luck in your hunt.

 

[Ron20324]

I'm surprised no one has mentioned a kellet.

 

[justsomeguy]

I'm surprised no one has mentioned a kellet.

Oh no you didn't!

 

[Gunni]

Ol' Keith is likely under his desk wishing he never brought the question up! You will need to consider the depth of water you typically anchor in, whether you have a windlass, type and weight of anchor. The newer spade-style anchors will work on much shorter scope, and a heavier anchor stays more securely set. With a 30 ft boat I would also be careful not to put too much weight (chain) in the bow. Always have a PlanB - secondary anchor.

 

[mm2347]

I think the "standard" recommendation is a boatlength (30') of chain and the rest nylon. From my experience chartering in the San Juans, I would go for about 200 feet total length which would give you a scope of 7:1 in 25 feet of water at high tide (assuming your bow is 4 feet above the water.) The chain is enough to keep the rode pulling horizontally on the anchor in most protected anchorages. Nylon is a great natural shock absorber. And you avoid putting a large weight of chain in your bow where it will encourage "hobby horsing" in a seaway.

All chain is a necessity where coral could cut a fiber rode. The other advantage is that its 5:1 scope allows boats to lie closer together in a crowded anchorage. But I am not aware of any other advantages to an all chain rode. As noted by the need for a windlass, such a rode is significantly harder to recover than nylon and chain without a windlass.

I am aware of no solid data that shows a five to one chain rode will hold any better than a seven to one nylon and chain rode.

Our boats do not apply an even or steady load on the anchor. The jerky movement increases the forces greatly and should be absorbed before transmitted into the boat or down to the anchor. A straight chain will not do it. A chain is pulled straight in moderate winds that are of little concern of dragging an anchor but all the shock forces from gusts or waves are transmitted thru the chain into the boat. Make sure if using all chain to use a snubber to absorb the shocks.

 

[jviss]

I could very well be wrong, but I always thought all-chain was better than chain to rope. Most big, expensive boats I see, cruising around, use all chain. I just assumed, because of the weight, that all-chain provided a straighter pull on the anchor. And, chain last longer - less fear that your rope is at end of life, and might part.

We use a snubber - only about 10 or 12 feet from the cleat to the hook. I don't recall the size, maybe 3/4", three-strand nylon. I made it maybe 15 years ago, so it's probably due for replacement (!), but if it parts it won't be a disaster.

So, what's better? I say chain. Straighter pull on the anchor, and much longer service life. And, less expensive, long term, if you are replacing your nylon rode ever five years. I just priced both, 5/8" nylon is $1.49/ft., 5/16" G4 chain is $3.40/ft. (at Defender). So, for a little more than double, you can have chain.

I wouldn't do chain without a windlass, though. If you're hauling by hand, I think rope is the answer.

 

[thinwater]

If yo look at the Rocna simulation linked by Alan Gomes, you would need not 1,000 lbs. to straighten out the chain, but 4,500 lb. The model shows some catenary left at 720 lb.s pull (320 daN).

So, what is it? 1,000 lbs. pull in a 50 kt blow, or 4,500 lb.? Of course, it depends on your windage, i.e., your boat. How much pull does a 36' sloop generate in 50 kt?

Personal experience; in a 50 kt blow, once, many boats on rope dragged, most on all-chain didn't. Shallow, sand anchorage (Block Island New Harbor).

a. I (we) did not say the chain was straight, we said the last link had just come off the bottom. Thus, both figures are correct. Without double checking the figures, 1000 pounds (150' 1/4-inch chain) will lift the last link and 5000 pounds will get it pretty darn straight. Yes, there is a little catenary remaining at 720 pounds. Google "catenary calculator" and you will find many on-line versions that will give you this information. A standard engineering calculation, though you do have to correct for the density of water and dynamic effects.

b. A boat generates peak loads about equal to the ABYC H-40 table 1 figures in the worst case, shallow water, all chain case. If the rode is nylon, if there is enough chain to maintain catenary, or the boat is well protected from waves, the figure can be about 3-5 times less and more steady. You can get a load cell and measure this. I have and others have. Google it. Many variables. But as a rough rule, if you can pull in the chain in 15 knots (50 pounds?), then 50 knots will be 50*(50/15)^2=560 pounds plus 2-3 times that in the gusts and waves (pulling by hand is more of an average, since there is lost of catenary). So yes, 1000 pounds is reasonable. I've seen readings much higher than that on my 32-foot catamaran (chain + 35-foot snubber).

c. "... many boats on rope dragged, most on all-chain didn't." Though anecdotal reports are vital to building understand, this sort are difficult to evaluate. For example, it may also be true that " ... only 5 percent of the boats on rope dragged, but 10 percent on chain dragged," or that "... many boats with undersized anchors dragged, but few with larger anchors (folks with a windlass tend to use bigger anchors)." Personally, I've dragged with an undersized Delta (I upgraded later) on all chain in 20 knots and stood strong with a Fortress 1/2 that weight in the same location in 50 knots on all rope (with enough scope). Thus, my experience says this is a poor correlation, though chain is a little more mistake proof. Folks have circled the world using rope; I suspect they knew how to use it.