Cruising Anchor Chain Length

[model 10]

[QUOTE=kas_
Can one humbly ask how much you think should be down at 25kts if you have a correctly sized, new gen anchor and all chain in 5m of water?


I can't answer for that guy, but I would have every bit of 150' out and we have all the good stuff. Even with no wind I would have a 100' down. I've had our oversize new gen anchor drag several times, I don't trust it any more than any other anchor.

[s/v Jedi]

With a cqr, delta, happy hooker etc. You will need 6:1 or more but for any decent and modern anchor, 3:1 is just fine. We did 40+kts on 3:1

[Budawang]

This is a very interesting thread. We have a 43 foot monohull weighing around 15 tons with 70 metres of 5/16th and a 65 lb (just over 27kg) Manson Supreme anchor. After 5 months of full time cruising along the east coast of Australia, it has set and held like glue. We haven't, however, anchored in extreme conditions.

When we bought the boat I was concerned the 5/16th (8 mm) chain wasn't sufficient but have come to the conclusion that chain diameter isn't as important as having a good anchor and having enough length to let out lots of scope. Correct me if I'm wrong, but there is no way high quality 8 mm chain will break even in extreme conditions. The only advantage of heavier chain is to have more catenary. However, as has been pointed out, in extreme conditions you are not going to have any meaningful catenary regardless of the chain diameter. As has also been pointed out retrieving 3/8th chain in a deep anchorage is also more problematic which could also be a safety issue. If my windlass fails I might have a chance of manually raising my 5/16ths but 3/8ths would be significantly harder . Money is perhaps better spent on a bigger/better anchor, longer chain and good snubber than buying larger diameter chain.

[kas_1611]

Originally Posted by Ecos

I can't answer for that guy, but I would have every bit of 150' out and we have all the good stuff. Even with no wind I would have a 100' down. I've had our oversize new gen anchor drag several times, I don't trust it any more than any other anchor.

Ecos, fairy nuff and an honest answer. So you would lay out 30.5m of chain in 5m of water (6:1 scope) even in calm conditions? That will make you Mr Popular in some of the anchorages we visit. And you go as far as 9:1 in 25kts, in some anchorages at 5m water depth that would put your swinging circle into the "keel on the bottom" areas and again make you Mr Popular with others trying to escape a blow.

Sometimes we don't have the luxury of being able to drop more than 4:1, even in a blow and yes I too have had my oversize Vulcan drag in 45kt winds but that was due to the chain wrapping round the shank and tripping it rather than an catenary or holding issues. Chain wrap being even more of a potential problem if you have 9:1 down.

That said if you have the space then I agree put out more when the weather forecast indicates it might be necessary but at the same time try to figure out why an oversize new gen anchor keeps dragging. My Vulcan actually landed upside down once, they ain't foolproof that's for sure.

[Dockhead]

Originally Posted by kas_1611

. . . Chain wrap being even more of a potential problem if you have 9:1 down.

. . .



And fouling. The area of the seabed swept by the anchor chain goes up by pi times the square of the distance to the anchor and becomes enormous pretty fast. This is a serious issue in rocky places with boulders on the bottom, and one reason Dashew has stated is why he prefers short scopes as little as 2.5:1 (using enormous anchors).



It's one of several good reasons not to use excessive scope.

[noelex 77]

Originally Posted by Black Eagle

4:1 scope in "25 knots of wind (higher in the gusts)"??
The issue is not the catenary or all chain vs chain+rope rode;
it's just a poor scope!!

Originally Posted by Ecos

I can't answer for that guy, but I would have every bit of 150' out and we have all the good stuff. Even with no wind I would have a 100' down. I've had our oversize new gen anchor drag several times, I don't trust it any more than any other anchor.

In his location more than the deployed amount of chain would not have been viable.

There is no need to be fearful of this type of combination (4:1, 5m depth, 25 knots) in a reasonable substrate. Part of the reason for having good anchoring gear is in order to be able to utilise these type of situations.

Moving to an alternative anchorage will still be needed on occasions, but by fitting a better and larger anchor you can minimise the times when this is necessary.

[Yellow bird]

Originally Posted by kas_1611

4:1 with a modern anchor is good for 25kts if you set it properly. Hell I've hung on at 25kts with 3:1 down albeit only for an hour or so. Anchor was well dug in by the end of the wee blow.

Can one humbly ask how much you think should be down at 25kts if you have a correctly sized, new gen anchor and all chain in 5m of water?

The pictures talk by themselves! "Set properly" is much differnt from that (also if the anchor is well dug). No escuse!
If you don't have at least 5/8 meters laying on the ground (with modern anchor, with old model better more) behind the anchor, it means you have a poor scope, and that is a rule with every kind of anchor and every kind of rode!

Sometime,if you are in conditions that don't allowed more scope, you can put a weight on the chain after 7/10 meters behind the anchor, but it's just a palliative, and not the best solution!

[Auspicious]

Originally Posted by Black Eagle

4:1 scope in "25 knots of wind (higher in the gusts)"??
The issue is not the catenary or all chain vs chain+rope rode;
it's just a poor scope!!

Wait. Just what about 25 kts is a big deal?

Originally Posted by Ecos

I can't answer for that guy, but I would have every bit of 150' out and we have all the good stuff. Even with no wind I would have a 100' down. I've had our oversize new gen anchor drag several times, I don't trust it any more than any other anchor.

As noted above 9:1 is a lot of chain. Do you run over to every new boat coming into the anchorage to tell them how much chain you have out? Over winds of just 25 kts?

Originally Posted by Black Eagle

If you don't have at least 5/8 meters laying on the ground (with modern anchor, with old model better more) behind the anchor, it means you have a poor scope, and that is a rule with every kind of anchor and every kind of rode!

Sometime,if you are in conditions that don't allowed more scope, you can put a weight on the chain after 7/10 meters behind the anchor, but it's just a palliative, and not the best solution!

You haven't followed the math. I commend Alain Fraysse's page on rodes. You'll also find that a kellet is useless in high wind and only really plays a useful role in very light wind.

[Yellow bird]

Originally Posted by Auspicious

Wait. Just what about 25 kts is a big deal?
.......................................

You haven't followed the math. I commend Alain Fraysse's page on rodes. You'll also find that a kellet is useless in high wind and only really plays a useful role in very light wind.

I totally agree,
it's just what I said "but it's just a palliative, and not the best solution!"
It was just a comment to Noelex pictures, and a replay to kas.

I don't mind if 25Kts is a big deal or not,
I just said that If you don't have at least 5/8 meters laying on the ground behind the anchor, it means you have a poor scope; regardless of the wind, of the depth, of tha ratio (4:1 is more different in 5m depht than 10m than 15m depth), of the kind of anchor.
It is just a basic rule of anchorage.

[Dockhead]

Originally Posted by Black Eagle

I totally agree,
it's just what I said "but it's just a palliative, and not the best solution!"
It was just a comment to Noelex pictures, and a replay to kas.

I don't mind if 25Kts is a big deal or not,
I just said that If you don't have at least 5/8 meters laying on the ground behind the anchor, it means you have a poor scope; regardless of the wind, of the depth, of tha ratio (4:1 is more different in 5m depht than 10m than 15m depth), of the kind of anchor.
It is just a basic rule of anchorage.

Well, I disagree. It's desirable to have chain on the bottom. That means no angulation on the anchor, and all your catenary is working. But it is quite often not possible in strong conditions even if you let out all your chain, and there are situations where it is better not to exaggerate scope even if you could.


If you plug numbers into Alain's spreadsheet (sta_hom.xls), you'll see.

[Yellow bird]

Originally Posted by Dockhead

Well, I disagree. It's desirable to have chain on the bottom. That means no angulation on the anchor, and all your catenary is working. But it is quite often not possible in strong conditions even if you let out all your chain, and there are situations where it is better not to exaggerate scope even if you could.


If you plug numbers into Alain's spreadsheet (Attachment 201595), you'll see.

And that it's the reason (or one of the reasons) why in strong conditions you can't use only one anchor, but maybe two, or rope on shore or in the mangrovias, or both!
Because if it not possible have enoght rode your anchor doesn't work at its best.

Nobody can persuade me that in the case of the pictures of Noelex, that it is what I'm talking about, with more rode the anchor doesn't work much better!

[model 10]

[QUOTE=Auspicious As noted above 9:1 is a lot of chain. Do you run over to every new boat coming into the anchorage to tell them how much chain you have out? Over winds of just 25 kts?




Sounds like I'm anchoring on a different planet. We almost always anchor in about 10', as does everybody else around me. Nobody goes around warning boats about their scope. 100' of chain is the least I would ever use and we have a 25kg Rocna for a 17,000 lb boat. I can't imagine being at anchor with only 50' of chain on the bottom and a reef in the background.

[noelex 77]

Originally Posted by Black Eagle

And that it's the reason (or one of the reasons) why in strong conditions you can't use only one anchor, but maybe two, or rope on shore or in the mangrovias, or both!
Because if it not possible have enoght rode your anchor doesn't work at its best.

Nobody can persuade me that in the case of the pictures of Noelex, that it is what I'm talking about, with more rode the anchor doesn't work much better!

More scope will lower the angle of the rode and you are perfectly correct: the anchor will work better with a longer scope, considerably better.

The optimum scope is not reached until 10:1 or more.

But good anchoring gear has plenty of reserve to cope with these moderate conditions at 4:1.

None of the other solutions you have suggested (other than the kellet, and I think we agree that this would make a minimal improvement) would have been practical, so the only option facing the skipper was to leave.

The reason for fitting good anchoring gear is to avoid having to do that as much as possible.

[jkleins]

[QUOTE=Ecos;2997727][QUOTE=Auspicious As noted above 9:1 is a lot of chain. Do you run over to every new boat coming into the anchorage to tell them how much chain you have out? Over winds of just 25 kts?









Sounds like I'm anchoring on a different planet. We almost always anchor in about 10', as does everybody else around me. Nobody goes around warning boats about their scope. 100' of chain is the least I would ever use and we have a 25kg Rocna for a 17,000 lb boat. I can't imagine being at anchor with only 50' of chain on the bottom and a reef in the background.[/QUOTE]



Well, if you are really anchoring in 10ft then with another 5ft up to the attachment point you have a scope measurement of 15 ft so 100 ft is really only 6:1 or so and in shallow water adding another 15ft probably doesn’t change the dynamics of those anchoring around you just because most people like to stay a little further away so small adjustments don’t make much difference.

Do the same thing in 25ft of water (30ft x 6 = 180ft vs 30 ft x 5 = 150) This is probably getting closer to a boat length and could possible change someone’s decision about where to anchor. If you were to go crazy and put out 9:1 (30ft x9 = 270ft) I am sure the 90 feet extra that you will swing will change the dynamics of everyone around you in a moderately crowded anchorage. I certainly never plan for people I anchor around to have more then 5:1 scope.

Jim

[Auspicious]

Originally Posted by Ecos

Sounds like I'm anchoring on a different planet. We almost always anchor in about 10', as does everybody else around me. Nobody goes around warning boats about their scope. 100' of chain is the least I would ever use and we have a 25kg Rocna for a 17,000 lb boat. I can't imagine being at anchor with only 50' of chain on the bottom and a reef in the background.

Originally Posted by jkleins

I certainly never plan for people I anchor around to have more then 5:1 scope.

Jim's experience aligns with mine. The 9:1 you specced for 25 kts, which isn't that much wind, is unexpected.



And yes, people do warn other boats about their scope if they are doing something unusual. 9:1 is unusual. Bahamian moor is unusual. Bow and stern anchoring is unusual, shore ropes are unusual (most places). It's polite to let people know when you are doing the unexpected.