Scope, All Chain Rode and Breaking Strength

[cr180]

Originally Posted by JordanH

This thread made me scratch my head...


Presumably, if you need 350' of scope, then your options are 200' of heavy chain + 150' of anchor line, or 350' of lighter chain. At 7:1 scope, that's anchoring in 50' of water.


Your anchor gear works best when the strain on the anchor itself is parallel to the bottom so that the anchor drives in, instead of pulls up and out.


Now think about the angle of your dangle... with 150' of rope road leading to the bottom (remember, only 50') that means you have your 231 lbs, laying flat on the bottom, neatly laid out and no real weight pulling your bow down. In the other case, you have an arc of chain, pulling down your bow and the rest of the lighter chain on the bottom. You have less weight driving the anchor in and more weight holding down your bow. Why would you want that?



I've never heard of a 30' boat breaking an anchor chain due to overloading it. Dragging, sure, but never the chain actually breaking. (Assuming no rust, good condition, yadda yadda). So I don't think "breaking strength" is relevant.


In either case, both gear weighs the same on deck so no advantage to sailing.


I simply don't see any arguments for anything but the heavy chain. This isn't a halyard or jib sheet where lighter&stronger is what you want. This is ground tackle. You want heavy. The chain provides a great deal of holding power.


To really drive the point home, examine what you have if you anchor in 10' of water. You want a scope of 70'. That's 1/5th of the light chain, or 46.2lbs. 70' of the heavy chain is 80.85 lbs. So for the same scope, same anchor, you have almost double the weight of anchor chain on the bottom. The heavy chain wins in just about every case I can see.

Agree.

[MVDarlin]

Note. If you change chain size you will need to change yhe cat head on your winch to match.

[Estica]

Interesting conversation. I’ve never heard a story of a boat breaking loose because chain in good condition (not rusted) broke. It’s always a story about anchor dragging or other hardware coming apart

[cr180]

Originally Posted by Estica

Interesting conversation. I’ve never heard a story of a boat breaking loose because chain in good condition (not rusted) broke. It’s always a story about anchor dragging or other hardware coming apart

Yes, you are exactly right. Ground tackle is a system. Often the bottom holding conditions trump even conservatively sized ground tackle. But the larger chain does add weight which increases catenary in any depth of water and thereby not only adds elasticity but helps the anchor holding.
It should never be about the chain breaking, it should always be about not dragging.

[rslifkin]

Keep in mind, if you're going to add weight, adding it to the anchor will help more than the chain. I'd rather have 100 lbs of chain and 100 lbs of anchor than 150 lbs of chain and 50 lbs of anchor. The bigger anchor will give much more margin for short scope, poor bottoms, etc.

[cr180]

Originally Posted by rslifkin

Keep in mind, if you're going to add weight, adding it to the anchor will help more than the chain. I'd rather have 100 lbs of chain and 100 lbs of anchor than 150 lbs of chain and 50 lbs of anchor. The bigger anchor will give much more margin for short scope, poor bottoms, etc.

Why choose one or the other. Agree with your comments about the benefit of larger anchor. Compliment that with the benefits of larger chain for unexpected severe weather situations.

I run all 3/8 HT chain with an 80 lb Manson.

[thinwater]

Originally Posted by rslifkin

Keep in mind, if you're going to add weight, adding it to the anchor will help more than the chain. I'd rather have 100 lbs of chain and 100 lbs of anchor than 150 lbs of chain and 50 lbs of anchor. The bigger anchor will give much more margin for short scope, poor bottoms, etc.

I think we all generally agree. But there is more.


Say I am lifting the anchor by hand in 15 feet of water. Do I want a 35-pound anchor and 200 feet of 3/8" chain (1.4#/ft), or 56# lift. Or 150# anchor and a 30' chain leader (121# lift). Clearly, the latter rig is lighter but impossible to weigh by hand.


Or say you have a V700 windlass with a max pull of 700 pounds, but probably only 350 sustained without blowing a breaker. Now, lets say the water is 50 feet deep. In the first case the windlass is pulling 105 pounds. In the second case about 145 pounds (some rope weight). Closer. Anchor in 100 feet of water and the heavier anchor is starting to look good. The deeper the water, the more the chain penalty. But the greater the savings on scope.



So a compromise makes sense.


And then there is the matter of shock absorption. The lighter the chain, the greater the need for a snubber, though in shallow water you will need it either way.


It comes down to understanding your personal needs. Personally, I anchor in shallow water, chain catenary doesn't really do much, so the lighter the chain the better and use longer scope (which still isn't much). In deep water, the same answer for different reasons (even light chain gives good catenary). In middle depths, heavy chain works for many people, reducing scope and giving a cushion in the moderate weather they sail in.

[captain38]

A really important question! The responses I have read so far do not mention the most important factor in deciding what chain. Anchoring safety and security is the NUMBER ONE factor to consider, and after that weight in the bow, windless, etc, etc.
So holding power should be the number one decider, and the total weight of of your ground tackle IN THE WATER is a top factor of holding power. You want as much weight in the water as possible.
Therefore, I would choose 5/16" HT for both weight and holding power strength.
Good choice to avoid rope rode, as it is vulnerable to chafe when the wind stops and the rope sinks to the bottom.

[Breaking Waves]

Originally Posted by cr180

I run all 3/8 HT chain with an 80 lb Manson.

One thing I realize from this thread is that the terms 'heavy' and 'oversized' mean different things to different people.

I personally don't consider 3/8" 'heavy' for a 47' (high windage) boat. I have seen serious (engineless in high latitudes) 30'ers with 12mm chain - I consider that on the heavy side but prudent for their circumstances. Back in the day, we had 3/8" on our 37'er for rtw tropical use. 3/8" for a 47'er seems just normal to me. And we ran 120lb anchors on our 47'er (which I personally considered perhaps a little on the 'heavy' side but not by much for a high latitude boat) so 80 also does not seem at all heavy.

I guess there is a 'relative to other cruisers I hang with' to how people use these terms.

[KP44]

Originally Posted by Offshore58

I have a 70,000 lb motor yacht 58' x 16'
I have 5/16 HT chain with a couple of bad links.
Is there repair links and are they recommended ?
Will they go thru the gypse ?
Is this a good enough chain for anchoring occasionally in the Exumas ?

That's funny.
I assume you're a sailor and this is humor.

[KP44]

Originally Posted by rslifkin

Keep in mind, if you're going to add weight, adding it to the anchor will help more than the chain. I'd rather have 100 lbs of chain and 100 lbs of anchor than 150 lbs of chain and 50 lbs of anchor. The bigger anchor will give much more margin for short scope, poor bottoms, etc.

In my experience, the heavier chain makes even a marginal anchor hold better. I will always use an oversized anchor but I will still use the heavier chain unless I need extreme rode length.

[rslifkin]

Originally Posted by KP44

In my experience, the heavier chain makes even a marginal anchor hold better. I will always use an oversized anchor but I will still use the heavier chain unless I need extreme rode length.

The heavier chain will help some, but the point is, the same amount of extra weight added to the anchor will help more. Generally, there's only so much weight that's reasonable to carry in ground tackle (at least until you get into very large boats), so I'd rather have a very generously sized anchor and somewhat lighter (but still plenty strong) chain.

[cr180]

Originally Posted by Breaking Waves

One thing I realize from this thread is that the terms 'heavy' and 'oversized' mean different things to different people.

I personally don't consider 3/8" 'heavy' for a 47' (high windage) boat. I have seen serious (engineless in high latitudes) 30'ers with 12mm chain - I consider that on the heavy side but prudent for their circumstances. Back in the day, we had 3/8" on our 37'er for rtw tropical use. 3/8" for a 47'er seems just normal to me. And we ran 120lb anchors on our 47'er (which I personally considered perhaps a little on the 'heavy' side but not by much for a high latitude boat) so 80 also does not seem at all heavy.

I guess there is a 'relative to other cruisers I hang with' to how people use these terms.

Point noted. But if you undersized size ground tackle based on the notion that the ABYC tables have a safety factor of 3 to 5 on 42 knot wind data, then ???

[cr180]

Originally Posted by rslifkin

The heavier chain will help some, but the point is, the same amount of extra weight added to the anchor will help more. Generally, there's only so much weight that's reasonable to carry in ground tackle (at least until you get into very large boats), so I'd rather have a very generously sized anchor and somewhat lighter (but still plenty strong) chain.

Understand, there’s a limit to how much each boat can carry. But if you are going cruising, the weight of tools, spare parts, clothes, provisions, full tanks, not to mention happy hour liquids, et al sets the water line down some in most boats. So the question is one of priorities. 3/8 HT chain weighs about 1.5 lbs/ft.

[rslifkin]

Originally Posted by cr180

Understand, there’s a limit to how much each boat can carry. But if you are going cruising, the weight of tools, spare parts, clothes, provisions, full tanks, not to mention happy hour liquids, et al sets the water line down some in most boats. So the question is one of priorities. 3/8 HT chain weighs about 1.5 lbs/ft.

I agree that ground tackle weight shouldn't be overly limited on most cruising boats. The issue is that most boats carry all of the ground tackle weight right up at the bow where boats are the most sensitive to added weight, so it's easier to end up with a weight problem there than in many other places.