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Anchor chain


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Here is a pic of our anchor. I don't know what make it is, estimated weight is 8kg and we have never used it, nor do we expect to.

However, having an anchor on board is a requirement so I would like to set it up with a length of chain, just in case.

The boat is 10.5m and 8 tonnes. The maximum depth we would ever anchor in is 3 meters on a mud bottom, maximum current 2km/hour.

Stowage is a bit of an issue so what would be the minimum chain size and length that I could safely get away with?

20190618_084059.jpg

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From its condition I would say the anchor has never been used and came with the boat, and if you think that one is small then you ought to see the little mini version on board as well.

It is intended to buy 8mm shortlink and I am aware of the old length of chain = boat length rule but because we don't have good stowage for chain and 8mm costs an eye watering NZD22 a meter, I was hoping given our anchoring conditions that we could get away with a bit less.

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The NZD22/meter was from the hardware store Leroy Merlin in Nancy. Since then I have found tested 8mm chain from the ship Chandler in Metz at €5.80/meter. But we are on our way to Toul at the moment and the Chandler in Metz doesnt arrange delivery. So we will try our luck in Toul where there are a few boatyards.

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Interesting about the Euro versus Chinese chain KM.

The 8 mm short link chain offered at €5.80/metre, assuming I can get my hands on it, is made in France, Grade 40, ISO 4565, whatever all that means.

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looks like a home made POS to me!

I've only just twigged as to what POS means, or rather what I hope it doesn't mean.

My opinion is that when you see the same bit of gear on a lot of different boats it's because it's a proven piece of equipment and well suited to its purpose. This is the case with my POS which is identical To everybody else's POS, differing only in size. They are found on private boats from around 8 - 9 meters all the way up to the 80 meter commercial vessels so obviously suitable for canals and rivers.

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Thanks to KM for a detailed description of the ins and outs of anchor chain. I have found a source of the 8mm grade 40 chain where we are here in Toul, cost €7 per meter, a bit more than the other guy but then I don't have to pay for delivery.

I'm reluctant to buy 10m of it.

I started this post querying whether I could get away with less than 10m of chain in my rode. There are two reasons for this. Firstly, here's a picture of the foredeck.20190620_084729.jpg

As you can see its not exactly well set up for handling an anchor. The only place I can see to stow an anchor rode is in a plastic bin on the foredeck.

Secondly, everybody knows that in a chain/rope rode the chain should equal the length of the boat. Well, why? What is the correlation between chain length and boat length? So if you have a 15m super slippery ultra lightweight low volume low windage race yacht you need 15m of chain in your rode. Yet I with my 10m high wooded heavy bluff bowed dumpy putterboat only need 10m of chain. So how does that make any sense?

So, kicking all the 'everybody knows' sacred cows, here's another one. Whilst chain does of course provide protection against chafe from the sea bottom and it limits sheering, I do not believe that it does much to improve holding. I have been anchored twice on all chain in well over 60 knots of sustained breeze (in a yacht, not the putterboat). This is the sort of stuff that when you go forward to check your gear you crawl on your hands and knees - the wind is too strong to stand up in. in these conditions I note that the chain leaves the fair lead and enters the sea about 15m ahead of the boat and the chain is bar tight and dead straight. Not an inch of cantenary in it at all. So the chain will provide cantenary and thereby give a horizontal pull on the anchor in benign conditions, when you don't need it. And in severe conditions when you do need it, you don't get it. My opinion is that 8 and 10mm chain used by the average boater is too light to provide any useful benefit in terms of holding, exceptions in regard to chafe and sheering as noted above.

And that is why I am reluctant to fork our dollars and give myself storage problems when anchoring in canals may be regarded as anchoring in a puddle in a paddock. This is not the Hauraki Gulf.

Right, now I'll tie myself to the stake for my heretical comments on chain. Roll up with the matches.

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If the chain is bar-tight, surely the effects of gravity are working exactly the same way and the catenary force is still active - it still wants to pull the chain down?

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Of course in these conditions it is not possible to see the anchor stock but by implication if the chain is bar tight then the anchor stock is in line with the chain and not lying on the sea bed as it should be.

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Right, now we are off to collect the chain. I don't necessarily agree with the purchase for the reasons stated above but if your wife tell you to buy chain, then you buy chain. (Sigh)

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If that is the case Chris, the anchor will pull out. Once the angle is towards the surface, it relies purely on the shear strength and weight of the seabed material. Its essential that the pull is along the seabed to retain holding power. Hence, more scope for better holding. With a long scope, it does not take a huge weight to deflect the rode sufficiently to keep the angle of pull parallel to the seabed.

In your experience above, even when the chain looks bar tight and straight, it is almost certainly NOT going directly to the anchor, or it would not stay put...

IMO. Knot me would likely have more to say... 

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If that is the case Chris, the anchor will pull out.

 

I don't think it would. At a 10 : 1 scope in heavy conditions and assuming the anchor rode bar tight and the stock of the anchor in line with the rode then the angle of the anchor stock with the seabed would be 6°. If the flukes of the anchor rotate 30° either side of the stock which I think would be about that without actually measuring, then the anchor would still dig in.

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it depends on the depth, often in shallowish water the chain will appear to be straight when actually, depending on how much you have out, it is lying along the bottom. Given that most of the anchor chains Chris was once used to probably 2 links of that size would hold his previous H28 forever.  ;-)  ;-)

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It's a bit chilly today, but this summer's heatwave is due to start tomorrow around lunchtime with temps approaching 40°. So we are staying put today and I have been passing the time reading a great many scholarly articles on the benefits or lack thereof of chain induced cantenary in the anchor rode. Surprisingly, the results of a lot of research would be 50 : 50 either way. The best answer to the question would be 'it depends..'

So the benefits of chain in the anchor rode in terms of improved holding are not set in stone and therefore I feel a bit justified in my views.

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Hi Chris, interested in seeing what research you are looking at?  As a simpleton I can't imagine a situation where gravity, expressed through the catenary effect, wouldn't be a help in holding your anchor to the sea bottom.  I've been wrong before though!

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May be you could use anchor without chain in calm conditions and slide a prepared weight down line if it becomes windy. Save cost of chain. Less chafe would be advantage of a short piece of chain.

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