Maximum chain for stowage

[Ubergeekian]

Thank you for the account of how your previous chain broke. I think people were asking because it's almost unheard of for an anchor chain to break! Glad that it all worked out ok without too much trauma or damage done.

I'd never heard of it either. Although Jumblie has high bows and therefore a fair windage for a 26 footer, I can't believe that the steady windforce should have snapped the chain. Neither, as I wrote, was there much snubbing. So I'm pretty sure it must have been a rusted, damaged or faulty chain link. That's why I'm replacing the whole chain - and going up a size because in my nice, simple book heavy chain is better than light chain!

The best bit was the timing. I'm quite glad it happened at 6am and not 2am!

 

[Robin]

Not terribly interesting, I'm afraid. Went for a wee trip to the north end of Bute. Anchored for the night - 20lb CQR plus all 15m which came with the boat out in about 3m or water. Last foot or so of chain before the anchor - the bit that lived outside - was a bit rusty, the rest looked and looks (what's left of it) fine.

By morning it was blowing nicely - 20kt gusting to about 35kt. About 6am a muffled bang was followed by the gentle thump as we drifted into the shore. Luckily Mr Yanmar did his thing and we motored slowly to Colintraive, picked up a mooring and sat out a real blow (for the sheltered waters of the Clyde) - up to 45 kts for extended periods.

We weren't violently snubbing when the chain broke and although 15m is not much (she lived on the East Coast for years) there was around 5x depth out when it went. The old chain is, I think, 7mm so I am going up to 8mm.

I had a look at the chain locker today. It's a wee bit difficult to tell how much room there is, since the old chain is sitting on a fair bit of braided rope, but from what Quandary says (thanks) I think there will be enough room for 45m. I shall ring the estimable Jane at Largs Chandlery tomorrow and ask her, if she has ordered a 50m bag of the stuff, to keep it all for me. Otherwise 30m will do ... for now.

Shallow water anchoring puts more load on the chain and many years ago when I was involved with laying and maintaining moorings, many of which were drying ones and therefore shallow water, there was some research into the reasons. Sadly I cannot remember the source or the reasons but the gist of it was that snatch loads hugely increase the load on the chain, more than the same snatching would in deeper water and probably because the catenary provided some snatch damping. It was especially valid in our mooring case where Truckline ferry in those days used to pass close by in Poole and send a wall of water across the moorings and especially so near to low water. I think I remember advice in the study to even incorporate old tyres into the riser chains as snubbers, but in our case we were using very much heavier chain and chose not to and never had one break.

In anchoring terms I have always been aware of this shallow water effect and laid out much more scope than the usual 3xdepth or 5xdepth calculations would suggest unless in deeper water. Where we are based the spring rise is only around 2 metres and waters are shallow thus for example in Studland we would anchor in under 4.5m of water or less at HW even with a boat drawing 2.02m. In such cases we would have probably 30m of chain out except for a lunch stop and we always used a nylon snubber line with a rubber mooring compensator wound into it, no snatch ever and much quieter. This has the added benefit of sweeping a larger radius of eel grass from the seabed too as seahorse deterrent. (joke Mr Trewhella and Garrick-Maidment honest...)

7mm chain seems odd to me. The usual sizes were 1/4", 5/16" or 3/8" so if you maybe had the old 1/4" size (6.35mm) that too could be a factor even on a small boat, I never had less than 5/16" or 8mm even on a 21 footer and on both our W33 and last boat a Sun Legende 41 had 3/8" or 10mm.

 

[blueglass]

we have the toppling over problem occasionally after a rough passage. I know its easily prevented by spreading the chain as it comes in, but we only have access to the chain locker from below, so with me at the anchor winch and SWMBO at the locker, that leaves nobody at the helm. Not impossible with a bit of toing and froing but is a tad awkward.

 

[Ubergeekian]

In anchoring terms I have always been aware of this shallow water effect and laid out much more scope than the usual 3xdepth or 5xdepth calculations would suggest unless in deeper water.

Agreed. That's why I had all 15m (I know, I know, it's not enough - "getting more chain" was top of my list of upgrades) out for 3m of water. But, as previously, it really didn't seem to be snatching.

7mm chain seems odd to me. The usual sizes were 1/4", 5/16" or 3/8" so if you maybe had the old 1/4" size (6.35mm) that too could be a factor even on a small boat, I never had less than 5/16" or 8mm even on a 21 footer and on both our W33 and last boat a Sun Legende 41 had 3/8" or 10mm.

I'm guessing. The new stuff looks bigger, but perhaps that's wishful thinking!

 

[Robin]

Agreed. That's why I had all 15m (I know, I know, it's not enough - "getting more chain" was top of my list of upgrades) out for 3m of water. But, as previously, it really didn't seem to be snatching.

I'm guessing. The new stuff looks bigger, but perhaps that's wishful thinking!

3m of depth is actually 4m or more to the bow roller height so 5 x depth would be 20m of chain, 5m more than you had on board.

My guess is you actually had maybe 1/4" chain, untested or calibrated and of dubious age and parentage. A decent length of nice new 8mm stuff from a reputable source with more of it to boot and a nice new snubber line made up as well should improve things no end!

We had 60m of chain on both our last two boats. No problem with tumbling on the W33 which had a goodly drop from the deck to the below deck locker, but on the Sun Legende with the windlass mounted on a plinth inside the anchor locker itself (lift up lid on deck) the drop was short and it needed the odd shove to clear the volcano out of the way when raising the anchor. Tumbling inside the locker after the chain was stowed did occur but never caused a problem with jamming when used next time.

 

[pugwash60]

I know it's not a popular theory amongst everyone on here but I still like as much friction as I can get between the chain and the seabed so the idea of paying 3 X as much for stainless chain which has much less friction (and I'm sure that that's right; it's much harder to pull in by hand as it's so slippery) wouldn't appeal to me. I have 90 m of chain and it's a pain to stow as I have to keep going below to knock over the pile and as I normally sail by myself it slows things down. On the other hand I once anchored with a 45 lb cqr on a rocky bottom and with the full scope out it just held the boat (Elizabethan 31) in 40-55 kts of wind, and I'm sure it was mostly friction doing the work, we did drag a bit in the gusts but only a couple of metres at a time and it gave me the option of stopping under a weather shore and having a cup of coffee and dinner rather than fighting the elements to get to a nicer anchorage.

 

[Ubergeekian]

3m of depth is actually 4m or more to the bow roller height so 5 x depth would be 20m of chain, 5m more than you had on board.

True. But 3 x depth was 12m of chain, 3m less than I had on board, and used.

My guess is you actually had maybe 1/4" chain, untested or calibrated and of dubious age and parentage. A decent length of nice new 8mm stuff from a reputable source with more of it to boot and a nice new snubber line made up as well should improve things no end!

Definitely not 6mm chain. The Jouster (lying Kirkcudbright, no reasonable offer refused) has 6mm, and it's bigger than that. I've just checked the 1986 bill, but it just says "25lb CQR with 5 fathoms of chain and 10 fathoms of rope, £146". There was certainly more than 5 fathoms there, and no join, so yes, unknown age.

I've just rung Largs to up my order, but alas they have got in a 30m length and not, as I hoped, a 50m one. So it'll be 30m for now - quite enough for what I do, especially since I have a 100m anchor warp as well - and I'll add more at some point in the future.

 

[Deleted member 36384]

Pile problems are nearly always associated with the hawse pipe. If you can place the chain locker directly below the hole in the deck and remove the hawse pipe you will not have any issues when letting go or weighing. Alternatively the hawse pipe needs to have the exit point much further from the top of the chain locker.

It is quite easy to make the hole water tight, with or without chain by shaping rubber block / or wood with a latex / soft elastomer profile. If the hole in the deck is offset then a half pipe (removable) that guides the chain over the top of the anchor locker can be rigged.

Its not conventional and you have to unship the chain from the anchor on passage as it wont be constrained by the hawse pipe.

That's my observation from trying to solve single handed anchor weighing issues.

 

[VO5]

I perioically paint the exposed portion of chain on deck with grey Hammerite, keeps the rust away. Also after rough sailing when convenient I make a point of spraying the exposed chain with fresh water anyway.

There are two main causes of rust in exposed chains, one being salt nestling in the nooks and crannies. This guarantees moisture gathering in the links and doing the mischief over time aided by the chemicals contained in the salt.

The other is the effect of industrial pollution.

In the chain locker chain rusts if stowed dirty.

I never stow the chain with mud clinging to it. I keep the chain flaked on deck and then hose it down when I can before stowing it. Then in the locker I give it a prolonged squirt with WD40 or similar.

 

[jdc]

optimal size of chain

Agreed. That's why I had all 15m (I know, I know, it's not enough - "getting more chain" was top of my list of upgrades) out for 3m of water. But, as previously, it really didn't seem to be snatching.

I recently did some calculations to establish if it's better to have a shorter but heavier length of chain or a longer but thinner one, assuming mixed chain-rope rode and a constant overall weight. This graph is for my boat - yours will be slightly different but same principle and conclusions can be drawn.

This graph plots on the y-axis, the total (mixed chain & rope) scope you need when anchoring in 10m of water against chain weight per meter - on the x axis, for a variety of wind forces, for a fixed total chain weight of 120kg.

It shows that you are always 'better' with a shorter but heavier chain. 'Better' is in inverted commas because I define it rather simply as the minimum rode length which just keeps the pull at the anchor horizontal.

We have also all been taught that rode length should be 10m + 3x depth or 5x depth - sorry, but this is complete mathematical bo**$^ks! Graph here, again for my boat (60m of 10mm chain, heavy 42' boat) but everyone's should be broadly similar, plotting for various wind forces the amount of rode required to keep the pull at the anchor near horizontal (near because I take anchor weight into account, but it's actually a tiny effect).

Overlayed in yellow and purple are the normal rules of thumb: the graph shows that when anchored in shallow water one should let out more scope than these suggest, and less when in deep water.

I bet all of us actually do, by instinct maybe, rather close to what my graphs show, so no real revelations, but it's comforting to me at least to understand the physics. Formulae, calculus, many more curves, a JavaScript plotter which allows you to enter parameters for your boat etc all available if anyone interested.