Upgrade chain size or use anchor angel?

[GrahamM376]

Which suggests that 10mm chain is 44% better than 8mm chain, for the same situation, which is quite an improvement.

Whilst any chain may be stretched straight in constant very high winds, I noticed quite a difference when we upgraded from 8mm to 10mm in that the 10mm, being heavier, had a better damping action with less snatching in gusting conditions. Following this train of thought, I would assume that an angel (which I've never tried) would further improve that?

 

[Pye_End]

But as I said before, to make it dead straight would need an infinite amount of load, or an zero weight chain, surely?

Rode weight may well need more force to make it straight, but can't see it needing an 'infinite load' to straighten it. Surely that would mean that any rope or chain could never be made straight horizontally? Perhaps there is a subtlety in the maths, and that the discussion here is making it effectively straight - ie enough to pass on substatial shock loads to the anchor? Cerrtainly mooring ropes can look completely straight, and thet are not zero weight.

 

[CaptainBob]

That seems so often the reality.
It's pretty rare I've wanted to anchor somewhere in a breeze and had space for an 11:1 scope.

LOL no, nor carried enough chain probably!

This anchor maths website is great. I'm just downloading MS's free XL spreadsheet viewer because he's made a sheet you can use to calculate required rode length etc, including an anchor angel in the maths also. The spreadsheet is available, with others, here:

http://alain.fraysse.free.fr/sail/rode/synthesis/synt.htm

Bums, doesn't work in the free viewer for some reason. And doesn't work in Open Office either. Shame.

 

[Chris_Robb]

I like top use a 20 meter length of 18mm nylon with a chain hook when the wind is up.

You set it some 10 to 15 meters out from the bows allowing the chain to dangle in a big loop. When the boat shears in gusts, it is just amazing as to how much the nylon stretches and eliminates the snatch loads.

Just make sure you protect the nylon where it goes over the bow roller.

I think that this could be more effective than an anchor chum (which I have never used). It also means that your rode is all chain, which is easier to recover on a windlass than a warp combination.

 

[bbg]

Rode weight may well need more force to make it straight, but can't see it needing an 'infinite load' to straighten it. Surely that would mean that any rope or chain could never be made straight horizontally? Perhaps there is a subtlety in the maths, and that the discussion here is making it effectively straight - ie enough to pass on substatial shock loads to the anchor? Cerrtainly mooring ropes can look completely straight, and thet are not zero weight.

I believe that is correct. No line can be made to be completely straight.

In the old days of shipbuilding, alignment of propellor shafts was accomplished by using tensioned wires. Even on those very strong, very light, highly tensioned wires, the effect of catenary could not be ignored. If it was, the shaft would be out of alignment.

So your anchor cable will never be "straight". Never. It might be tensioned enough to pull the whole thing off the seabed. But the tension required to get it even close to "straight" would tear it apart.

 

[CaptainBob]

Rode weight may well need more force to make it straight, but can't see it needing an 'infinite load' to straighten it. Surely that would mean that any rope or chain could never be made straight horizontally? Perhaps there is a subtlety in the maths, and that the discussion here is making it effectively straight - ie enough to pass on substatial shock loads to the anchor? Cerrtainly mooring ropes can look completely straight, and thet are not zero weight.

I do think it is impossible for them to be completely, mathematically, horizontal, despite what they appear to be. But it's a moot point as after reading that website link it's clear that the critical point is when the anchor is not pulled horizontal any more, and the chain does not need to be mathematically "straight" for that to happen.

 

[Coaster]

...I'd use a long snubber to reduce snatching.

I always use a chain hook and length of stretchy nylon as a snubber...

Would someone like to comment on how long the snubber should be? We use a 4m length of 14mm for general use on a 34' sloop of about 8 tons displacement, which is convenient and seems effective for moderate conditions.

I have 50m of 16mm octoplait ready to add to our 8mm chain if it's ever required although we've never used it. Should I make up a snubber longer than 4m for use in adverse conditions? If so, will a Witchard chain hook (as used on our 4m snubber) be strong enough? The geometry seems to be such that the snubber line would try to bend the 'shaft' of the hook.

 

[CaptainBob]

I like top use a 20 meter length of 18mm nylon with a chain hook when the wind is up.

You set it some 10 to 15 meters out from the bows allowing the chain to dangle in a big loop. When the boat shears in gusts, it is just amazing as to how much the nylon stretches and eliminates the snatch loads.

Just make sure you protect the nylon where it goes over the bow roller.

I think that this could be more effective than an anchor chum (which I have never used). It also means that your rode is all chain, which is easier to recover on a windlass than a warp combination.

We did have a short length of nylon with one of those rubber snubbers on, to a chain hook also. Perhaps the equivalent stretch of your longer line, with less line?

 

[Conachair]

Shame he hasn't also done the maths with an angel in the system.
.

There are some good spreadsheets in there which allow you to play around as much as you like with different size chain & angels & rope. Pretty pictures too
http://alain.fraysse.free.fr/sail/rode/synthesis/synt.htm

For instance, from sta_mix.xls....

In 10m of water to the bow, 30m of 10mm chain, 10m 19mm rope and 20Kg weight 27m away from the bow...

Takes 178Kg force on the chain to lift all the chain off the seabed. Without the 20kg weight it takes 132Kg to lift the chain. So you gain a bit but maybe less than you think. If you let out another 6m of rope you achieve the same thing. Increasing from a 4:1 to 4.6:1 will have the same effect as a 20Kg weight in the force it takes to lift the whole lot off the bottom.

EDIT.
Ooops, Just saw your other post, shame you can't get into the spreadsheets, very interesting.

 

[Searush]

FWIW I carry a heavy angel (25kg ish) for use in extremis. I fasten it to the bitter end of the chain & then use a shortish length of rope to get the angel on the seabed & lie to around 3x depth of rope.

Mostly the angel stays on or near the seabed, keeping the pull on around 30m of 8mm chain almost horizontal as it should be. On gusts it lifts but has never got anywhere near the surface judging by the angle of the rope & that stops any snubbing which would aggravate any chafe. You still need good anti-chafe tho! The boat is a 31' Pentland Ketch.

I try to avoid situations where I need to use it, but "poo" happens as they say & I have been glad of it once or twice. But the effort of setting & recovering it seems to increase as I age.

Final comment, I sail in waters with 10m tides & with a twin keel so get in as shallow as I can, sometimes letting her dry out at LW.

 

[Salty John]

Would someone like to comment on how long the snubber should be? We use a 4m length of 14mm for general use on a 34' sloop of about 8 tons displacement, which is convenient and seems effective for moderate conditions.

I have 50m of 16mm octoplait ready to add to our 8mm chain if it's ever required although we've never used it. Should I make up a snubber longer than 4m for use in adverse conditions? If so, will a Witchard chain hook (as used on our 4m snubber) be strong enough? The geometry seems to be such that the snubber line would try to bend the 'shaft' of the hook.

I use a 5m length of three strand nylon which I tie to the chain with a rolling hitch. I stopped using a chain hook after the first couple of months - I find they tend to drop off. I prefer a lighter line - I used 12mm on a 41' ketch - because the stretch is the important bit.

 

[John Barry]

Use at least one boat length of octoplait as a snubber. It stretches by about 20%, and removes much of the snubbing force from pitching, yawing and gusting.

I'd suggest that you look at updating your chain from 8mm to 10mm or preferably 11.5mm, but I realize that there's a weight penalty when not at anchor.

From your original post (12m boat, 40m of 8mm chain, 10m of water) you'd have 8° of angulation at 18Kn or wind and about 10° at 23Kn (angulation is the angle the rode makes with the horizontal (0°) at the anchor).

Is 40m your full chain length? Do you have warp on the end to extend it? I can prepare a table for various windspeeds and depths if I know the maximum chain length and the acceptable angulation (which depends on your anchor).

 

[Chris_Robb]

We did have a short length of nylon with one of those rubber snubbers on, to a chain hook also. Perhaps the equivalent stretch of your longer line, with less line?

You need far far more stretch than can be given by a rubber snubber. My snubber line - usually in bad weather out from 10 to 15 meters, with give a couple of meters stretch. That is why they are so effective in stopping the snatch loads when shearing around.

We also have a 4 meter length with hook we use when anchored stern to any where, to tail the chain load off the anchor winch. You should never leave your chain tensioned on the anchor winch.

 

[Chris_Robb]

I use a 5m length of three strand nylon which I tie to the chain with a rolling hitch. I stopped using a chain hook after the first couple of months - I find they tend to drop off. I prefer a lighter line - I used 12mm on a 41' ketch - because the stretch is the important bit.

Agree that 18 mm warp is probably too heavy - but still stretches incredibly. Chain hook?? I don't have a problem anymore with it failing off the chain, but agree that a rolling hitch is just as good.

 

[AngusMcDoon]

A while back for a bit of an experiment I anchored a 10m trimaran (so quite a bit of windage) in 5m of hard sand using the tiniest aluminum Guardian anchor and 50m of ex-climbing rope - 9mm nylon - in 25kts of wind. No chain at all. It was like being moored to a bungy the amount of stretch in the line. It held without problem all day, and it was a real effort getting the anchor out. My conclusion was scope and stretch are good things to have.

 

[GrahamM376]

Would someone like to comment on how long the snubber should be? We use a 4m length of 14mm for general use on a 34' sloop of about 8 tons displacement, which is convenient and seems effective for moderate conditions.

I use about the same length of 12mm stretchy 3 strand, boat's around 9 tons loaded, 38ft. The added advantage of the rope snubber is in stopping the chain under tension rubbing against the hull in wind over tide situations.

 

[vyv_cox]

I use 12 mm braid on braid nylon, originally intended for tethering a large balloon. I usually let between 2-3 metres over the bow roller and cleat it another metre or so away. Stretch is visible in any sea. I have used the same line ever since we began cruising, 1989.

 

[GrahamM376]

You should never leave your chain tensioned on the anchor winch.

Having had to repair a mate's windlass for him after he'd torn the two 2 rear studs out of it and bent the front ones 45 degrees, I would agree with that. He'd never heard of a snubber.

 

[lw395]

FWIW I carry a heavy angel (25kg ish) for use in extremis. I fasten it to the bitter end of the chain & then use a shortish length of rope to get the angel on the seabed & lie to around 3x depth of rope.

Mostly the angel stays on or near the seabed, keeping the pull on around 30m of 8mm chain almost horizontal as it should be. On gusts it lifts but has never got anywhere near the surface judging by the angle of the rope & that stops any snubbing which would aggravate any chafe. You still need good anti-chafe tho! The boat is a 31' Pentland Ketch.

I try to avoid situations where I need to use it, but "poo" happens as they say & I have been glad of it once or twice. But the effort of setting & recovering it seems to increase as I age.

Final comment, I sail in waters with 10m tides & with a twin keel so get in as shallow as I can, sometimes letting her dry out at LW.

Not having a windlass. I used to keep the kellet nearer the boat, so when it came to weighing anchor, you don't have to lift chain at the same time as the kellet.

 

[John Barry]

Not having a windlass. I used to keep the kellet nearer the boat, so when it came to weighing anchor, you don't have to lift chain at the same time as the kellet.

A kellet is more effective the nearer the anchor it is.