Using a ball weight on the anchor chain

[RaymondR]

Originally Posted by MathiasW

So, just a double check on this... At that kind of light wind, I guess at least 100 metres of that chain were on the seabed. If I assume a 10 mm chain (likely yours is less than that), then in water the chain will weigh 2 kg per running metre. The friction force in sand is close to 100% of the weight of the chain, which then gives about 200 kg of holding power by sheer friction - as long as the chain does not start moving. Even sideways.

On the other hand, in 15 kn of wind, a vessel of your size has perhaps a wind load of only 100 kg. Which means, the chain can well support it without the need of an anchor.

But then double the wind speed to 30 kn, which is a factor 4 in the wind load, and the chain is not able anymore to hold your vessel. Even worse, when you need the friction force, in a strong blow, it is not there anymore because the chain has raised above the seabed.

So, not a good idea at all not to have an anchor.

And btw - if anchors really were not needed, then why would commercial large ships not drop the anchor entirely? (Pun intended ) If an anchor is not needed, cost optimisation to increase margins would require you to get rid of it. But they all still have it...

Cheers, Mathias

Anchor Chain Calculator

Hi Mathias,

you got it bro.

The chain alone holding power it the product of the weight of the chain actually on the bottom and the chain/bottom friction factor. Since friction factors mostly never reach unity(generally lucky to make 0.5 in my experience) your total holding is probably going to be less than say 100-150 pounds force. A well dug in anchor along with the contribution of the on-bottom chain will usually do better than this.

[Baby tug]

Y’all are debating this over and over and over again , I watch the video not Long ago of a woman that probably weighed about 100 pounds pulling up an anchor with all chain for a 36 foot sailboat , this is a couple that is sailing all over the world , I would say that most of the holding power in most of the sets that you do with your anchors is pretty much dead weight laying on the bottom , so whatever deadweight added would be beneficial, pretty much all large commercial ships anchors do very little to nothing it’s all the dead weight of the chain pretty much a fact look it up , I don’t know why you’re debating this , A plow anchor completely buried doesn’t really have that much holding power , what is this debate about

[Uncle Bob]

Originally Posted by Baby tug

Y’all are debating this over and over and over again , I watch the video not Long ago of a woman that probably weighed about 100 pounds pulling up an anchor with all chain for a 36 foot sailboat , this is a couple that is sailing all over the world , I would say that most of the holding power in most of the sets that you do with your anchors is pretty much dead weight laying on the bottom so whatever deadweight added would be beneficial, pretty much all large commercial ships their anchors do very little to nothing it’s all the dead weight of the chain pretty much a fact look it up , I don’t know why you’re debating this , A plow anchor completely buried doesn’t really have that much holding power what is this debate about

So I take it you don't bother with an anchor??

[RaymondR]

We've done the friction thing from the chain on the bottom so let's now take a look at what's going on at the anchor.

So the anchor digs into the substrate and the flukes form a flow barrier to an irregular cone of soil which the horizontal force on the anchor then forces the cone through the body of substrate. Consequently a conical shear surface is formed with a base of the projected area of the anchor flukes and a height dependent upon the angle of repose of the material from which the substrate is formed.

Lets assume the an angle of repose of 30 degrees and a base diameter of the cone of 20 inches. So the hypotenuse is 10"/cos 60 = 20" the area of the surface of the cone is 1.5708*10"*20"=314.16 sq inches. Now if we assume that the anchor has buried down until it has found soil with a shear strength of 5 psi we get a horizontal displacement resistance of 314.16*5=1,571 pounds force.

So there we go. our chain which weighs say 300 lbs lying on a surface which provides a friction factor of 0.5 is going to provide a restraint against horizontal displacement of 300*0.5=150 lbs and our anchor buried down into soil with a 5psi shear capacity is going to provide 1,571 lbs of resistance.

[s/v Jedi]

Originally Posted by RaymondR

We've done the friction thing from the chain on the bottom so let's now take a look at what's going on at the anchor.

So the anchor digs into the substrate and the flukes form a flow barrier to an irregular cone of soil which the horizontal force on the anchor then forces the cone through the body of substrate. Consequently a conical shear surface is formed with a base of the projected area of the anchor flukes and a height dependent upon the angle of repose of the material from which the substrate is formed.

Lets assume the an angle of repose of 30 degrees and a base diameter of the cone of 20 inches. So the hypotenuse is 10"/cos 60 = 20" the area of the surface of the cone is 1.5708*10"*20"=314.16 sq inches. Now if we assume that the anchor has buried down until it has found soil with a shear strength of 5 psi we get a horizontal displacement resistance of 314.16*5=1,571 pounds force.

So there we go. our chain which weighs say 300 lbs lying on a surface which provides a friction factor of 0.5 is going to provide a restraint against horizontal displacement of 300*0.5=150 lbs and our anchor buried down into soil with a 5psi shear capacity is going to provide 1,571 lbs of resistance.

That would mean the chain still provides 10% of holding power, which is more than I would have thought…

[RaymondR]

Originally Posted by s/v Jedi

That would mean the chain still provides 10% of holding power, which is more than I would have thought…

Lot of assumptions but probably in the ball park. Be mindful that the assumption of most of the chain is on bottom for the example but I suspect most would not be at maximum load on the anchor.

In another life I was involved in a project where it was proposed that thousands of feet of chain on each of eight anchors be utilized to anchor a floating oil rig in a place where the bottom was a thin layer of sand over a hard limestone bottom. There was not enough chain available so piles were drilled into the bottom as anchors.

[MathiasW]

Originally Posted by s/v Jedi

That would mean the chain still provides 10% of holding power, which is more than I would have thought…

At most, and I guess it is still optimistic, for two reasons:

A) The amount of chain that is lying on the seabed gets smaller and smaller as the wind / swell picks up. So, the contribution that the chain's friction can make gets smaller and smaller, when we would really need it.

B) The friction coefficient of 0.5, or an optimistic 1.0, as I had assumed based on Taylor's work, is only valid as long as the chain does not move. Even sideways. When the chain starts to slip, the friction coefficient gets reduced, which is a well known effect of friction in general. And as it is likely that part of the chain will move at least sideways in a lot of swell, when the vessel moves a lot, it will mean that the contribution friction can make is even less.

So, bottom line, I would not want to rely on what friction can do for me.

Cheers, Mathias

Anchor Chain Calculator

[MathiasW]

Originally Posted by Baby tug

Y’all are debating this over and over and over again , I watch the video not Long ago of a woman that probably weighed about 100 pounds pulling up an anchor with all chain for a 36 foot sailboat , this is a couple that is sailing all over the world , I would say that most of the holding power in most of the sets that you do with your anchors is pretty much dead weight laying on the bottom , so whatever deadweight added would be beneficial, pretty much all large commercial ships anchors do very little to nothing it’s all the dead weight of the chain pretty much a fact look it up , I don’t know why you’re debating this , A plow anchor completely buried doesn’t really have that much holding power , what is this debate about

Quite obviously, watching a video is not the same as actually living on the hook, as I happen to do. I can assure you that in 80% of my anchoring it is not the dead weight that is holding my vessel in place - at least for an hour of the day. We have squalls coming in regularly, in Costa Rica we had 40+ kn wind every afternoon. We have been in tight anchorages where we could not pay out enough chain - and slipped in a squall as many around us did as well. And I have seen a few vessels ending up on shore, unfortunately.

Do not be misguided when seeing somebody pulling up an anchor "easily". It is a technique you can develop, and the force required is much less than the anchor holding power, as it is a vertical pull, and ideally you used the rocking of the vessel directly over the anchor to loosen the anchor before attempting to weigh it.

As to big commercial ships - there is a reason why they are not allowed at anchor when it blows really hard and have to take to sea then. Our vessels can sustain far more wind at anchor than a commercial ship can, if our anchor gear is well designed. And as I said before, even the big boys need the anchor, or they would have done away with it ages ago and saved that expense. I think we can safely trust commercial enterprises to cut costs wherever they can. If they don't, there must be a reason...

I guess we will keep having this discussion as long as there are comments like yours coming in.

Cheers, Mathias

www.anchorchaincalculator.com

[boat driver]

Originally Posted by thinwater

Please take a length of chain (the amount the will be in the sea floor, perhaps 40 feet) and tell me if you think it would even hold your dinghy in a blow. You will be able to drag it with one finger.


Really, comparing heavy fishing boat practice with recreational boat practice is pointless. They have little in common.

A ship uses chain to anchor the ship, the anchor itself simply provides an added drag to the chain. This is simply due to the concept that a ship could not lift an anchor of calculated size.
secondly, one tug boat technique is unwind the tow cable in a big loop and come back alongside the barge.

and yes, comparing a ship to yacht is not really realistic, but advertising an all purpose anchor is just as impractical. There is no one type all use anchor, and if in doubt, simply look at the types of anchors on different ships.

[RaymondR]

Hi again Mathius,

even with a unity friction factor and with all the chain on bottom the best you could do is 300# of restraint.

And my guess as to the actual would be in the 1.5-3.0 range favouring the bottom end.

[MathiasW]

Originally Posted by RaymondR

Hi again Mathius,

even with a unity friction factor and with all the chain on bottom the best you could do is 300# of restraint.

And my guess as to the actual would be in the 1.5-3.0 range favouring the bottom end.

Hi Raymond,

yes, indeed, it can never amount to much, really....

Cheers, Mathias

[mrcarson]

Originally Posted by MathiasW

Alright, here we go again... this myth never seems to die...

That is just utter nonsense. If the chain is holding you, you would not need an anchor to begin with, would you. Just put some chain out and you will be good.

The anchor will hold the vessel, nothing else. The chain will, by way of gravity, rise and fall and thereby act as a temporary energy storage to absorb shock loads. Assisted by elastic snubbers or ropes.

If the chain does not have a catenary shape before the gust / swell hits the vessel, it cannot absorb the shock load and the anchor will be directly exposed to this load increase, if you do not have an elastic snubber / rope on the other side to compensate.

For this reason it is important that there is enough chain, and yes, in this sense the chain is holding you as well, as it absorbs some of the shock loads. The same can be said about a very elastic snubber.

But do not think it is the chain's friction on the seabed that is doing this. That friction is only a tiny contribution. You will realise this if you try to pull 20 metres of 10 mm chain stretched out on the beach. Rather easy! And a joke for just about any vessel to pull away in seconds.

The chain ONLY contributes via gravity, absorbing energy burst as potential energy when getting lifted off the seabed. In deep water it can form a very nice catenary and then will work very well, even in a storm. In shallow water it cannot.

Cheers,

Mathias

https://anchorchaincalculator.com

https://trimaran-san.de/die-kettenku...atiker-ankert/

Mathias.
Have you ever seen the size of SHIP Chain links. they can weigh up to 1/2 ton and more each. I've been anchoring for a while. Mostly Yachts etc NEED the pick to stick a point into the bed. but heavier chain can hold. I've seen Admiralty and navy film of pick and chain trials. back in the 50/70's.
Mainly Bulk and Tankers. The picks just laying there. Lots chain out and just rising and falling with the sets, but never all down to pick.
as long as you lay plenty
I was a crane operator in prev life Back in '60/70'sas well as a diesel Tech. Often went into local oil refinery to lift and change the mooring chains every 5ish yrs. Tanker moorings where they lay just off and discharged.
MONSTER mussels on there, one was a full meal Yummm. Talking to crews and skippers enlightened you a lot to the anchoring and running off rather than heading for harbour.
NOTHING will hold any vessel in REAL bad weather. The further offshore the safer.
We used to oxy cut the chains into 3 or 5 link lengths and use them as the tug and work boat mooring anchors. after tidal movement had buried them in the sand along the coastline (divers checked)

[mrcarson]

Originally Posted by MathiasW

So, just a double check on this... At that kind of light wind, I guess at least 100 metres of that chain were on the seabed. If I assume a 10 mm chain (likely yours is less than that), then in water the chain will weigh 2 kg per running metre. The friction force in sand is close to 100% of the weight of the chain, which then gives about 200 kg of holding power by sheer friction - as long as the chain does not start moving. Even sideways.

On the other hand, in 15 kn of wind, a vessel of your size has perhaps a wind load of only 100 kg. Which means, the chain can well support it without the need of an anchor.

But then double the wind speed to 30 kn, which is a factor 4 in the wind load, and the chain is not able anymore to hold your vessel. Even worse, when you need the friction force, in a strong blow, it is not there anymore because the chain has raised above the seabed.

So, not a good idea at all not to have an anchor.

And btw - if anchors really were not needed, then why would commercial large ships not drop the anchor entirely? (Pun intended ) If an anchor is not needed, cost optimisation to increase margins would require you to get rid of it. But they all still have it...

Cheers, Mathias

Anchor Chain Calculator

Hi. As you say Stronger winds would probably drag her back. (8mm short link BBB) I was just experimenting (slight boredom with a little interest.
Yacht sized gear would need a pick and I've seen Bruce and CQR bury thenselves several feet into clay and mud. Not so much in sand. They tend to slide.
Back then (50's) I was decky on North sea Trawlers. We sometimes dropped a pick. In those days the kellick was then slid down to where skipper reckoned was half way down chain from bow to seabed.
The idea being. big waves/rough water. The lump would absorbe enough of the rise/fall so as the load/pressure, never much. went past the point of contact with seabed. Hence negating most if not all loading/Pressure on contact point of pick with the seabed???. We never did such.
Usually. rough weather (Real) We'd lay to engine ticking over, bow into seas for whatever time, hrs/days. Till shoal came. (We had lots of cod in the water in those days. Till the Spaniards and Russians started). or weather abated so we could fish again. It did get a bit bouncy out in North sea in Winter offshore. 110ft steel, trawler.
The trawl settled us down a lot though. Just not the rolling.

[StuM]

Originally Posted by mrcarson

Back then (50's) I was decky on North sea Trawlers. We sometimes dropped a pick. In those days the kellick was then slid down to where skipper reckoned was half way down chain from bow to seabed.

kellet: weight attached to anchor rode.
kellick (or killick): a small anchor attached to a rope (often a "jury rig" consisting of a stone attached to the rope)

[mrcarson]

Originally Posted by StuM

kellet: weight attached to anchor rode.
kellick (or killick): a small anchor attached to a rope (often a "jury rig" consisting of a stone attached to the rope)

Yea sorry Old fart mixing irish words again. I married 2 of them.