Anchor chain: downsize from 10mm to 8mm?

[Gary Fox]

Boat is 12 tons displacement. Set-up is Lofrans electric windlass, Rocna 25Kg bower, and other smaller anchors. 10mm chain.
(I want to downsize to a new-gen 20Kg bower when I find a suitable deal, and keep the R25 in the bilges for a rainy day, it is needlessly unwieldy).
There are various clear advantages to lighter chain. However it just seems too thin and fiddly to hold the weight of a double-decker bus crashing up and down on the swell, and the slightest nick or spot of rust, would cause dangerous weakness, as there is no metal in reserve.
I don't trust, (or want to pay for) anything other than standard chain.
I would have to buy a new gypsy but they are available off the shelf.
I feel safe with the 10 mil chain, but are there others with 12 ton boats who use 8mm contentedly?

 

[[2574]]

14t boat, grade 70 8mm chain, 25kg Vulcan bower anchor.

 

[dom]

My boat is around 50', and I use a 25kg Spade with 10mm chain.

I anchor a lot, did the calcs once and concluded that 8mm G80 would suit but never bothered switching.

If you, like me, are sticking with G30/40, I'd be inclined to stick with 10mm, but others will no doubt disagree!

 

[Tranona]

You can never apply enough load with your boat to get anywhere near breaking 8mm. Not only that it is 40% lighter and 40% cheaper. Holding power is a function of the anchor - chain plays very little part. If you can bear with the arguments, anchor threads to which Neeves contributes will explain it in detail. this may also help coxeng.co.uk/anchoring/chain/

 

[Gary Fox]

You can never apply enough load with your boat to get anywhere near breaking 8mm. Not only that it is 40% lighter and 40% cheaper. Holding power is a function of the anchor - chain plays very little part. If you can bear with the arguments, anchor threads to which Neeves contributes will explain it in detail. this may also help coxeng.co.uk/anchoring/chain/

I'm asking about the real, rusty world, where maths don't matter. Thanks for the link anyway, but I'm a lifelong member of the Catenary Counts club; hobbyhorsing is for another thread.

 

[Gary Fox]

14t boat, grade 70 8mm chain, 25kg Vulcan bower anchor.

Thanks, yes it is too pricey, or I would go that route.

 

[Gary Fox]

My boat is around 50', and I use a 25kg Spade with 10mm chain.

I anchor a lot, did the calcs once and concluded that 8mm G80 would suit but never bothered switching.

If you, like me, are sticking with G30/40, I'd be inclined to stick with 10mm, but others will no doubt disagree!

Yes I think I will stick at 10mm as well, it helps to bounce ideas off people, thanks,

 

[Gary Fox]

At least if I stick with 10mm, I will get a better catenary and the anchor will tend to set better (horizontal pull). Thanks chaps

 

[stranded]

14t boat, grade 70 8mm chain, 25kg Vulcan bower anchor.

Same but Bugel anchor. It does look flimsy but four years on in sometimes lumpy conditions we’re still on one piece. We wanted 100m and if we’d stuck with 10mm we’d have become a submarine heading into short steep seas.

 

[Tranona]

I'm asking about the real, rusty world, where maths don't matter. Thanks for the link anyway, but I'm a lifelong member of the Catenary Counts club; hobbyhorsing is for another thread.

The maths are there and they are real and provable There is zero advantage of 10mm over 8 in your situation. Even if Prof Knox calculations are out 5 times you would still be well in the breaking load of the chain In the "real world" with good quality galvanised chain properly looked after, why should rust ever be an issue. Catenary is a belief that is not proven by real facts, but I guess having it proved wrong as it has been many times causes real problems for people who live by beliefs.

Sorry for the rant but that is a proven scientific answer. If you don't intend changing when a proven alternative is offered, why bother to ask?

 

[Boathook]

I'm asking about the real, rusty world, where maths don't matter. Thanks for the link anyway, but I'm a lifelong member of the Catenary Counts club; hobbyhorsing is for another thread.

I've seen the catenary disappear at 20 knots on my 8mm chain, 9m cat. Just as well the anchor held well. This was in a sheltered anchorage so wind only.

 

[Deleted member 36384]

... I'm asking about the real, rusty world, ...

There isa degree of sense in allowing for wastage. i used to work for a charter company and we had many managed boats. When taking on managed boats, we would clean them from top to bottom and removing the anchor chain was part of that process. It was common to find the bitter end heavily corroded for a few meters having sat unused in a damp saline environment for most of its life.

 

[Gary Fox]

I've seen the catenary disappear at 20 knots on my 8mm chain, 9m cat. Just as well the anchor held well. This was in a sheltered anchorage so wind only.

Another reason not to downsize, thanks.

 

[Gary Fox]

The maths are there and they are real and provable There is zero advantage of 10mm over 8 in your situation. Even if Prof Knox calculations are out 5 times you would still be well in the breaking load of the chain In the "real world" with good quality galvanised chain properly looked after, why should rust ever be an issue. Catenary is a belief that is not proven by real facts, but I guess having it proved wrong as it has been many times causes real problems for people who live by beliefs.

Sorry for the rant but that is a proven scientific answer. If you don't intend changing when a proven alternative is offered, why bother to ask?

If you have read the quote you quoted, why bother to post?

 

[Neeves]

Thanks, yes it is too pricey, or I would go that route.

You don't make any sense, at all. You say you are in the catenary club and then imply you would buy G70 8mm if it were cheaper.

Make up your mind.

A decent snubber that costs peanuts will replace the absence of catenary.

Most 8mm chain has a UTS or 4t - you will never develop even 25% of that tension in your rode. If your chain is rusty - it will not improve with time, either get it re-galvanised or buy new chain. Gypsies are freely available but they cost, a lot. Though the savings you make on downsizing the chain, from 10mm to 8mm might go toward the new gypsy. If your windlass is old and the motor looking questionable - maybe think - new windlass. If you are baulking at the cost of G70 then buy 8mm G40 - it too is over strength for its specification. The chain may come from China, but you are quite happy with a Chinese made anchor - so why worry about Chinese made chain (which may come from the same people that make both anchor and chain)

But first up you need to decide if you are actually in the catenary club - or simply don't know. Once you have made your desires clear and they are logical it will be easier to help you.

How to: Dealing with Snatch Loads in an Anchorage

Anchor Snubber Tips

Anchor Snubber Shock Load Test | Practical Sailor

Even better - search out and buy a copy of the July issue of YM - there is an article there on rigging a snubber on a Mono hulls.

If you want more info on downsizing chain - send me a PM with a email address and I'll send you more detail.

And heed Tranona he is correct - but he may be confused as to your conclusions, as I am, as you either believe in catenary OR your intentions are dictated by money (not data).

Jonathan

 

[Tranona]

Indeed very confused. For example I have difficulty in imagining how a "slightest little nick or rust" would weaken chain that as you confirmed is four times stronger than the maximum load that the boat can generate. Nor how the chain is required to hold the weight of the boat crashing up and down in a swell, when this is not putting a load on the chain, but absorbing the movement. As you say a snubber can add to the absorption of snatch loads so that the anchor is left to do its job.

I guess the underlying issue is an unwillingness to accept that there is provable science underpinning the specification of the elements of an anchoring system and how they work together. Relying on feelings and beliefs is perhaps not a good idea when it is so relatively easy to follow the recommendations of suppliers of chain and anchors. In particular the link I gave to Vyv's site confirms the accuracy and reliability of manufacturers claims.

 

[Stemar]

It was common to find the bitter end heavily corroded for a few meters having sat unused in a damp saline environment for most of its life.

That strikes me as a good argument for a mixed rode. That way you get all the chain out from time to time and get a look at it. If you want all chain because you're anchoring in coral or something else that eats rope, at least have a couple of metres of line, which is an important safety factor if you have to leave in a hurry - cut and run!

It's a standard part of my winter maintenance to pull my entire rode out to check it; I'll then leave it on the deck for a couple of wet winter weeks to wash the salt out. I wait for a dry week afterwards before I put it away which, in a soggy Hampshire winter may mean a couple of wet winter months ?

 

[CAPTAIN FANTASTIC]

Under usual conditions, chains very rarely break; what breaks are the connections between chain and anchor and between chain and bow locker end. Surface rust does not affect the strength of the chain.

 

[doug748]

There are various clear advantages to lighter chain.

I think you have made up your mind however, unless you are pulling up the chain by hand or considering racing, I can't imagine what the advantages would be for you.

A new gypsy would cost an arm and a leg, to boot.

.

 

[Stemar]

I think you have made up your mind however, unless you are pulling up the chain by hand or considering racing, I can't imagine what the advantages would be for you.

A new gypsy would cost an arm and a leg, to boot.

.

I'm inclined to agree. If Gary needs new chain anyway, downsizing would make sense, likewise if he were heaving it up by hand and finding it difficult. Otherwise, while anything that adds lightness is a good thing, if it ain't broke...