Anchor chain size advantages

[conachair]

Originally Posted by thinwater

Agreed 100%. If you run the math on 50' of water with that boat that is exactly how it works, and that is why I have said there is truth in many points of view. For your situation it is a very good solution..

And here's the maths...
https://www.desmos.com/calculator/lszqjjyer4

So for 8mm chain with a force of 100Kg (which ain't a lot! )..

a scope of 4:1 in 10m water will have the chain just lifting off the seabed at the anchor, or about 3.8:1 in 12m water (just under 40')

Feel free to check the equations anyone.

[brianlara 3]

Originally Posted by conachair

And here's the maths...
https://www.desmos.com/calculator/lszqjjyer4

So for 8mm chain with a force of 100Kg (which ain't a lot! )..

a scope of 4:1 in 10m water will have the chain just lifting off the seabed at the anchor, or about 3.8:1 in 12m water (just under 40')

Feel free to check the equations anyone.

Who cares ?????????

[conachair]

Originally Posted by brianlara 3

Who cares ?????????

Anyone who is interested how the real world behaves.

[brianlara 3]

So me on the hook for the last 2,548 days, often in Tasman Sea open roadsteads, variously from 20' to 50' of water in winds regularly 30 plus knots minimum and gusting 60......!!
And this is'nt real world........me tinks you lost some marbles Sir Sonny Jim.
Bloody hard soaring like an eagle when I have to walk with...............(I'm being nice here/rules).
O M G ! ! !

H E L L O O O O.

[conachair]

Originally Posted by brianlara 3

So me on the hook for the last 2,548 days, often in Tasman Sea open roadsteads, variously from 20' to 50' of water in winds regularly 30 plus knots minimum and gusting 60......!!
And this is'nt real world........me tinks you lost some marbles Sir Sonny Jim.
Bloody hard soaring like an eagle when I have to walk with...............(I'm being nice here/rules).
O M G ! ! !

H E L L O O O O.

Physics will tell you what's happening to your chain in the 60Kn gusts, you don't know that bit of the real world. It's why the things we make work. Otherwise you're just guessing.
I live on the hook as well, good anchors work, what happens to the chain can be answered by simple equations. Matters not if you like it or not, the answers don't change.

[brianlara 3]

Once there were masses of theoretical experts such as yourself Sir who were also anchored to q w e r t y sea beds.
Along came a simple sailor, far less intelligent than his advisers....
he found that Hades was not in fact just around the (horizontal) corner.What he found was a land mass which was not aflame. A fool named Columbus.
My suspicion is that you have probably never ever anchored on the edge of oblivion or anything even close.
If I'm wrong then talk about.
Or continue by pm if you wish.
Public bun fights are so undignifying.

[conachair]

Originally Posted by brianlara 3

Once there were masses of theoretical experts such as yourself Sir who were also anchored to q w e r t y sea beds.
Along came a simple sailor, far less intelligent than his advisers....
he found that Hades was not in fact just around the (horizontal) corner.What he found was a land mass which was not aflame. A fool named Columbus.
My suspicion is that you have probably never ever anchored on the edge of oblivion or anything even close.
If I'm wrong then talk about.
Or continue by pm if you wish.
Public bun fights are so undignifying.

Yur guess is very wrong, anchored in many places far from help in some nasty condiions, experience and a good anchor will tend keep you safe. You are obviously very experienced and know what works. Pysics will tell you what the curve of your chain looks like. Two very different things. If you don't like it then don't cross any bridges because you don't like people calculating why things work

[jdazey]

Originally Posted by thinwater

The funny thing about this thread is that there is room for everyone to be partially right.

• Scope helps. Lower angle, more catenary (chain), more stretch (rope).
• Catenary helps. Not much in shallow water (<10'), but quite a bit in deep (>20 feet) water.
• A kellet can help, particularly by keeping rope away from the keel. The effect is about the same as the same mass of chain, obviously.
• More weight in the anchor helps. Hold is typically about mass^1.1, but the exponent is greater in some bottoms.

What is the correct safety factor, when folks speak of "sleeping at night" rather than anything calculated? How long is a piece of string?

It's rather silly to think that this could be one-size-fits-all. My answer (which I will not share) works for my boat, where I am.

That just about covers it.

[double u]

37' sloop, 2m draft (fin&skeg), all up ~7-8k kg
10mm chain, cqr 60lbs later bügel 20k, scope 1:5 or greater
watched groundtackle umpteen times (3rtws) snorkeling:
winds >22-25kn: chain lifted off bottom all the way to the anchor, catenary very difficult to ascertain, never did look like much
anchored in bays surrounded by mountains: lots of sailing around in gusty conditions as the heavy chain pulls boat forward in the lulls, boat "bearing away" up to ~60° in the gusts, rounding up & putting strain on groundtackle
next time: definitely smaller chain size!

[Olddave]

Hi W,
Interesting post, what depth? Obviously fairly shallow if you are watching with snorkel. I like your theory that the weight of the chain causes the boat to sail around on the anchor, but if it's shallow, maybe something else is contributing?
D.

[double u]

@10' of course only little sailing around
I'm talking ~30-60', the deeper the more pronounced the "sailing" is of course
with spare tackle (20kg brittany, 10m chain, remainder nylon) sailing around too of course, only the TWA much less=less load on the groundtackle (as boat is not being "brought up short" so intensely)

[Andy on Destiny]

I think that there is a lot of talk about ultimate Strength, but nobody breaks their chains. We use or Anchor for 90% of the summer that is about 180 nights and twice, or three times a day during our sail and ski season in the arctic. Its not about strength its about weight on the bottom, and heavy chain is weight. Sure you can put 100 kg of chain down which triples the weight of your Anchor but if you use a thin chain you have to let out more length to achieve that weight and there are plenty of times when you do not have that luxury of room in the anchorage.

I would choose a heavy chain any day over a light long one, and you save on buying a new gypsy plus when or if you ever need to re galvanise your chain will not lose half its strength that it will if it is a high tempered steel.

Our vessel is 48' 44,000lbs 1/2 chain,180' + 110lbs Lewmar claw port anchor and 60lbs spade on starboard, each chain also has 150' of rode but we never use it, that is there only if we ever are forced to anchor in deep water over 60' Note our chain weights 3lbs per feet so with full chain out we have over 500 lbs in the water. We do not move ever.

[Olddave]

W,
So it's pretty obvious that it's the weight of the chain.
Well I guess that's another reason to carry lots of chain with smaller diameter links. It would be interesting to get Brianlara3's take on that.
I am big on putting more chain out when the wind increases. Most of my anchoring experience comes from work boats. If we started to drag, we would let go another couple of shackles and drop the other anchor to the seabed directly under foot. That helps to reduce sailing around.
D.

[Olddave]

Originally Posted by Andy on Destiny

I think that there is a lot of talk about ultimate Strength, but nobody breaks their chains. We use or Anchor for 90% of the summer that is about 180 nights and twice, or three times a day during our sail and ski season in the arctic. Its not about strength its about weight on the bottom, and heavy chain is weight. Sure you can put 100 kg of chain down which triples the weight of your Anchor but if you use a thin chain you have to let out more length to achieve that weight and there are plenty of times when you do not have that luxury of room in the anchorage.

I would choose a heavy chain any day over a light long one, and you save on buying a new gypsy plus when or if you ever need to re galvanise your chain will not lose half its strength that it will if it is a high tempered steel.

Our vessel is 48' 44,000lbs 1/2 chain,180' + 110lbs Lewmar claw port anchor and 60lbs spade on starboard, each chain also has 150' of rode but we never use it, that is there only if we ever are forced to anchor in deep water over 60' Note our chain weights 3lbs per feet so with full chain out we have over 500 lbs in the water. We do not move ever.

Andy,
I fully accept what you are saying, I am just surprised that you only have 180' of chain.
You must tuck into some amazing places if you haven't got room to use more.
D.

[Andy on Destiny]

Hi Dave,

Yes generally we are in very tight anchorges, I am not fond of stopping overnight with guests to have to get up midway through because of a wind shift, so we use heavy short tackle with a scope of 4: 1.

Overall it is a weight issue, sure longer chain would be great but we have 2 working windlasses so we had to have less chain in the locker. We moved the chain locker 1m at to help distribution. But I would still rather have a short heavy chain.

Cheers Andy