Anchor Chum

[hattie]

I am looking to buy a 25kg anchor chum. I have not seen these for sale anywhere. Can anyone point me in the right direction as to where I might be able to get one and how much they cost?

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[Deep_6]

I have seen them advertised in the Compass catalogue but can't recall the weight.
I have used a 55lb scale weight before as a chum and it worked very well.

Try this link also: http://www.highlandecom.com/anchor/<P ID="edit"><FONT SIZE=-1>Edited by Deep_6 on 01/08/2003 23:15 (server time).</FONT></P>

 

[hattie]

Thank you so much for your reply. I have contacted Caley Marina and have asked for a price list for their different weights of anchor buddies. Much appreciated!

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[Deep_6]

Your welcome and happy sailing.
M

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[craigbalsillie]

Re: Anchor Chum (newby alert)

What's an anchor chum?



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[chippie]

Re: Anchor Chum (newby alert)

I know them by the brand name of anchor buddy. Basically a weight that is attached to the anchor warp to create a more horizontal pull and act as a shock absorber so motion is transmitted to the line and not the anchor.

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[craigbalsillie]

Thanks for that. nm

.

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[hylas]

A Marketing gadget...

Sorry to disturb this thread.. but an anchor "Chum" or buddy or sentinel or angel or...
is just one more "Gadjet" to have on board..

The weight of the chain has nearly NO action in the holding of an anchor as well as for shock absorbing effect.. and adding a "chum" will not increase the holding of a bad anchor..

Holding is related to the SURFACE AREA burried on and also with the angle of pulling... the "chum" will have NO action on the surface and a negligeable action on the pulling angle..

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[SlowlyButSurely]

Re: A Marketing gadget...

Nonsense dear boy. If you don't believe me try this simple experiment:
Lay 50 metres of 3/8 chain out on a sandy beach. Now try dragging it along. You'll find that you can, just. Next add the smallest CQR you can find. Now attempt to pull the chain!



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[vyv_cox]

Employment for a chum

Actually, this weekend we saw an excellent example of a case where a chum would have been very useful. Sunday morning on the Haringvliet, no wind, sunny and warm. By lunchtime a sea-breeze of about force 4 had set in and there are few places where one can get out of the chop. One such is behind the breakwater at Middelharnis. Towards the outer end this is a notoriously difficult place to anchor because the depth goes from about 15 metres to 3 metres in a boat length. We watched boat after boat make several attempts to get their anchors to bite but every one dragged at least once. The effective way seemed to be to let out an excess of warp and to let the boat move back very slowly, ensuring that the pull came as close to, or even beyond, horizontal. I remarked to Jill at the time that a chum would have helped a great deal.

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[Jacket]

Re: A Marketing gadget...

Rubbish. Dig out your catenary (sp?) equations from school physics and do the maths. For a typical weight of chum to have no effect on the snatching loads on the anchor, the yacht would be ahving to exert a dynamic pull of about 350 tonnes. Even allowing for a yacht exerting dynamic loads of about 10 times its own weight (and 'd have thought that it would have to be pretty gusty for that) you'd need a pretty big yacht to exert that sort of pull. OK, so the numbers are a bit debatable, depending on what you view as a useful reduction in snatching load, but shurely it shows that a chums not totally useless?

Putting out a similar weight of chain would have a similar effect, but drastically increase your swinging circle. If you're relying on warp, then a chum's probably worth a try.

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[MedMan]

Re: A Marketing gadget...

The weight of the chain has a major influence on the holding power of an anchor for the very reasons you have given to suggest that it doesn't!

You are correct in saying that two of the most important (but not the only two) factors influencing holding are surface area embedded and the angle of pull. Whilst the weight of chain does not affect the area embedded it has a dramatic affect on the angle of pull. Try this simple experiment in your garden:

Set up the clothes line as taught as you can so that it is straight - the condition you are trying to avoid with your anchor chain. Now wrap a bag of sugar (1 kg) in a cloth and hang it from the middle of the line and look at the dramatic change in angle of the line. If you still need convincing, repeat the experiment with 25 bags of sugar and just try pulling on the end of the line to bring it back to a straight line.

The curve in which an anchor chain lies under the influence of gravity is known as the catenary. Any physicist or engineer (I am neither) could produce you an equation to calculate the shape of the curve. The factors you have to put into the equation are the weight per unit length of the chain and the pull exerted upon it by the yacht. The heavier the chain the greater the pull needs to be before the length of chain next to the anchor is pulled above the horizontal.


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[hylas]

Re: A Marketing gadget...

The purpose of my previous answer was to intiate the discussion and for me the opportunity to “KILL” some old beliefs.. Thanks to all who have answered.. I will try to give an answer to all of you..

SlowlyButSurely

I already have followed your suggestion.. some time aggo and together with an engineer of the National school of engineering of Monastir, I went to a beach with some anchors, a tractor and a lap top computer equiped with a strain gauge..

At first we have tested a small prototype of a new design of anchor (now well introduced in the market).
With a small 3 (three) kg model, we break 6 consecutive times a 12 mm diameter nylon rope before changing it for a 16 mm diameter rope.. The small 3 kg anchor held 1475 daN...

Then we had tested the chain only.. It was 810 cm of 8 mm chain weigthing 11.75 kg (nearly four time the weight of the anchor) the holding was 31.2 daN..

Now, look at the figure:
For the anchor, the holding ratio was 1475 / 3 = 491 time the anchor’s weight
For the chain, the ratio was 2.65 time its weight
The percentage of holding given by the chain was 2.1 % or let’s say NEGLIGEABLE..

Then my conclusion: “this is the anchor which hold the boat and not the chain.. “ (or in your case, if it is the chain, it is time to think changing your anchor.. :0) )


vyv_cox

Thanks for your experience.. you said that “that a chum would have helped a great deal. “ But wich proof of that do you have?? Did you try one and what was the result??

The “Chum” proposed at the beginning of this thread was 25 kg (or in the water 21.5 kg..) the weight of a 10 mm chain is 2.25 kg by meter, or 10 meters of 10 mm chain have roughtly the same weight of the previous “chum”
I believe that 10 meters more of chain will have the same effect of the “chum” and are both cheaper and much more easy to use...

Jacket

Sorry but it seems that we dont use the same catenary formula.. I use a small Excel software to make all the calculation (I can send it to anybody who will ask for it at my personal E.mail adress: hylas@free.fr)
It seems obvious that a pull of 350 tons is not required to lift a 25 kg weight... It must be something wrong in your calculation???

Let’s try again.. On a boat anchored with 30 m of 10 mm chain in 5 meters of water height
With a 30 kg “chum” located near the bow roller, the pulling effort is the same than with the chain only = 175 daN
With the same “chum” located near the anchor, the result is improved: 331 daN and the improvment is 156 daN,
if the “chum” would have been located in the middle of the chain, the improvement would have been only 78 daN
Then I have to agree with you: a chum is not totally useless but it’s action is not very important compared with the holding of the anchor.. (156 daN for a 30 kg chum) and could have been easily remplaced by the same amount of chain..

The swinging circle did remain nearly the same, the only difference is that you reach the maximum radius with a little stronger wind gust and this will be exactly the same if you are using a chain or a rope rode..
When your moring line is pulled straight, chum or not chum, your radius is the same..


MedMan

As shown before, the weight of the chain has ony a negligeable influence on the holding power of the anchor: 2.1 %... (assuming that the chain is still lying on the bottom)

The weight of the chain has a negligeable action on the angle of pull: in the previous example, to lift 30 m of 10 mm chain from the horizontal, a pull of 175 daN is enough... with a 25 to 30 knots of wind, your chain is already bar tight and no more horizontal.. (calculated using the catenary equation)


Now.. my turn to ask questions???

1°) What is exactly the use of the chum??
- To reduce the swinging radius?
- To reduce the pulling angle on the anchor shank?
- To damp the peaks of pulling force?

2°) where should the chum be placed??
- near the bow?
- Near the middle of the line?
- Near the anchor??

3° ) what is your opinion about the “ANTI-CHUM”..

Have you ever think of attaching your biggest fender in the middle of your mooring rode??
- With no or light wind, your line will be lifted up, reducing your swinging radius..
- The pulling angle on the anchor shank is maximum and the efficiency of your anchor is minimum.. but who care? As there is no or only light wind..
- When the pulling force increase (with the increase of wind..) the fender is pulled down, the pulling angle decrease and the efficiency of the anchor increase proportionnaly with the increase of wind..
- The buoyancy of the fender has a damping effect against the peacks of the pulling force..

And last.. you don’t have to charge your boat with unnecessary weights nor to invest in expensive equipment as you already have a fender on board..

By experience, I know that anchoring and mooring are certainly the two topics which are still keeping a lot of wrong beliefs....

Peaceful anchorages to all..

Alain


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[chippie]

Re: A Marketing gadget...

Could you please explain to me why it is deemed important to have at least some chain between the anchor and the rope. I was under the impression that it caused the drag to be more horizontal at the anchor. Some older traditional anchors had very long shanks to achieve the same effect.
A mate of mine did some diving off the boat and as a matter of course had a look at the anchor. In mild conditions the(weight of) chain seemed to be holding the boat with minimal set on the anchor.
Have I been misinformed, or is your post only relating to the anchor buddy?

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[Strathglass]

Caley Marina have about half a dozen lying on the floor just as you enter the showroom.

Iain

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[MedMan]

Re: A Marketing gadget...

Hylas!

You say that “anchoring and mooring are two topics which are still keeping a lot of wrong beliefs.” With the greatest of respect I would suggest that you are guilty of introducing a number of “wrong beliefs” yourself and, far from clarifying the situation, you are confusing it.

I do not doubt that your beach tests with anchors and a tractor yielded useful information about the relative holding power of different anchors, but they were a 2D simulation of a 3D problem. Pulling an anchor with a tractor ensures that the pull is always horizontal. Whilst it is an accepted scientific procedure to eliminate all variables but one in order to investigate the effect of changing the one that remains – in your case the type of anchor – one must never forget that the results obtained give information about only that variable, not the real-world situation.

I am bemused by the description of your test using chain only. No-one to my knowledge has ever suggested that the friction of chain on the sea bed contributes significantly to the holding power of ground tackle. I am surprised that you found that it contributed as much as 2.1%. The importance of the weight of the chain is in maintaining a horizontal pull on the shank of the anchor, the all-important variable that you eliminated in your tractor tests.

Simple physics tells us that any force above the horizontal can be resolved into two components; one horizontal and the other vertically upwards. It is the vertical component that causes the anchor to break out and the greater the angle, the greater the vertical component. Did you do any tests to compare the breaking out force required for different angles of pull?

You have quoted some figures purporting to relate to the real-world 3D situation, but you have not made clear what you mean by them. You say that: “On a boat anchored with 30 m of 10 mm chain in 5 meters of water height with a 30 kg chum located near the bow roller, the pulling effort is the same than with the chain only = 175 daN” What do you mean by “pulling effort?” The effort required to do what?

I agree with you that 10 metres of extra chain will have a similar effect to adding a 25kg chum and it is certainly easier to deploy. However, the point has already been made that, in some circumstances, adding a further 10m to one’s swinging circle can cause problems of its own.

You say that: “I have to agree with you: a chum is not totally useless but its action is not very important compared with the holding of the anchor.” You cannot separate the two in this way. The figures that you have obtained for the holding power of an anchor are from your 2D non-real-world experiments and only apply to a horizontal pull on the anchor. The whole point about the catenary of chain, with or without a chum, is that it maintains that horizontal pull in the real-world 3D situation that we actually live in.

Taking this assertion one stage further, the minimum length of chain required in any given wind-speed is that required to ensure that at least one link of the chain is lying flat on the sea bed. Any more gives a wider swinging circle than necessary; any less and the pull will rise above the horizontal and dramatically reduce the holding power of the anchor. A chum enables the same situation to be achieved with less chain and, therefore, a smaller swinging circle.


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[vyv_cox]

Re: A Marketing gadget...

There's a lot of good data on anchoring at <A target="_blank" HREF=http://www.dulhunty.com/dmp1.htm>http://www.dulhunty.com/dmp1.htm</A> I cannot say that I agree with his anchor recommendation and the site omits some well-known European designs but there is a lot of basic information, especially warp loads due to windage.

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[SlowlyButSurely]

Re: A Marketing gadget...

Alain,

I am somewhat mystifed by your reference to the chain becoming bar taut. I've been using the same 35lb CQR with 3/8 chain for the last 17 years and I have never seen it anywhere near bar taut, even in a gale. In fact I find it very hard to believe that with a scope of chain 3 times the depth of water it could be pulled bar taut before the chain broke.

When I have been able to observe the anchor and chain under load, in the med, there has always been a substantial length of chain lying along the bottom.

Could you please explain how this practical experience can be reconciled with your catenary calculations?

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[hylas]

Re:sorry for the delay..

Sorry for the delai… I was practicing anchoring in a small isolated cove on the south of the island of Tenerife.. (and with 40 knots of wind..) and I didn’t have any connection to Internet… I’m back again now into the “civilisation” in the small marina of San Sebastian of the island of la Gomera…

Dear Medman..

Sorry for introducing a number of “wrong beliefs”.. This topic of “anchors tests” has been deeply discussed with all world wide specialists of anchors.. and the conclusion was that there is no perfect method of testing wich will perfectly reproduce the real anchoring conditions..

I have tested anchors, both by pulling them in the water from a beach with a tractor and as well in deep water, pulled by a boat..
It is easier to have more standart results with the first method.. pulling anchor with a boat, with the same anchor digg in nearly the same ground, you can have differences of several hundreds of daN..
When you can precisely place the anchors you are tested very close to the track of the previous test.. results are much more reproductibles..
Regardless the method of tests.. they are all very instructives about the behaviour of various anchors and oabout the comparative results..

During discussions about anchors and anchoring, I have been told quite often that it is the chain and not the anchor which hold the boat.. I didn’t invent it.. and this is wrong.. the friction of the chain is negligeable..

The belief that “the weight of the chain is in maintaining a horizontal pull on the shank” is also a wrong one.. or, let’s say, it is perfectly rigth with light winds, when nobody cares about anchor’s holding.. but wrong with strong winds (more than 25/30 knots) when holding is realy important.. For me, the ONLY purpose of the chain is to avoid wearing of the rode in contact with the sea bed..

I can not agree more with you about the two forces: the horizontal and the vertical one.. and this repartition is related to the angle of pull.. which is itself in relation with the SCOPE… The relation of the anchor holding power to the angle of pull is different for each anchor, but generaly speaking very well known..

The “Pulling effort” (175 daN) of my previous example was not the force required to have the mooring line perfectly straight, but the force required to lift the last link of the chain from the horizontal.. (you are perfectly right to ask the question and I apologize as I was not precise enough..)

You are right again when you said that “adding a further 10m to
one’s swinging circle can cause problems of its own.” But if this is the case, as far as I’m concerned, I’m prefer to anchor elsewhere..

But NO, “The figures that I have obtained for the holding power of an anchor are not from my 2D “non-real-world experiments” but are computed using the “catenary formula” or as you said “the real-world 3D situation that we actually live in.”.. and it will be by far more efficient to decrease the angle of pull by adding more lenght of rode ( and will not be related to the force of the pull) than using any type of “chum”..

The question of the “smaller swinging circle” is also a “wrong belief”.. With a “chum” and no or low wind, the swinging circle will not be related to the chum, but to the portion of chain lying on the bottom..
If you want your chum to be efficient for kepping the anchor’s shank as horizontal as possible, the “chum” has to be located as close as possible to the anchor shank.. and then will not have any action in reducing the swinging circle..
This was one of my previous question.. Where are you locating your “chum”??..


Dear SlowlyButSurely,

On a purely theoriticaly side, you are perfectly right: the force to have a chain perfectly “bar tight” is infinite..
But on the “real world” the force to lift the last chain’s link from the horizontal can be calculated using the “catenary” formula..

If you are relying on the weight of the chain to have the most horinzontal pull, you need to have the most heavy and the most long one.. Using a standard scope (I currently use 5) and a standard size (related to your boat charateristics) the pull of your chain will not longer be horizontal for wind speeds of 25/30 knots and the angle of pull will be related with the strenght of the wind.. the more wind, the biggest angle.. (or the lowest holding)(and more: to the peak of force given by the waves and this could be several TONS..)

If you are relying on the scope to reduce the angle of pull, (for example with only rope) your maximum angle will always remain the same, regardless of the pulling force..




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[GrahamC]

The original "Chum" anchor traveller referred to the saddle arrangement that slips over the set anchor chain and allowed the weight to slide down to where it would be most effective.
This item was manufactured in Edinburgh by an agricultural engineering firm called "Geo Henderson and Co", they supplied a weight as an extra but a 56lb was a cheap substitute, I like all the scientific stuff, but it did the job of reducing the swinging circle, and ironed out the snatch and jerk in a swell. Do not know who makes it now
Regards
GrahamC


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