How long a mooring line on the anchor snubber

tudorsailor

tudorsailor

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I need to replace the line on my anchor hook. I recall reading somewhere that the line should be nice and long so as to absorb shock as the anchor chain goes taut. To do this I would have to take the line back to the midships cleat.

However does this make sense? Surely with the caternary of the anchor chain, the change from big curve to completely straight is the main shock absorption, and adding lots of polypropylene will make little difference

Thoughts?

TudorSailor
 
tudorsailor said:
I need to replace the line on my anchor hook. I recall reading somewhere that the line should be nice and long so as to absorb shock as the anchor chain goes taut. To do this I would have to take the line back to the midships cleat.

However does this make sense? Surely with the caternary of the anchor chain, the change from big curve to completely straight is the main shock absorption, and adding lots of polypropylene will make little difference

Thoughts?

TudorSailor
Click to expand...

I add a mooring rubber shock absorber.
 
tudorsailor said:
To do this I would have to take the line back to the midships cleat.
Click to expand...

?

You can do that, but if you don't want to, just pay out the same length of line over the bow instead, and secure the end to a bow cleat / samson post / etc. Nothing says the chain hook has to be above the waterline.

tudorsailor said:
Surely with the caternary of the anchor chain, the change from big curve to completely straight is the main shock absorption, and adding lots of polypropylene will make little difference
Click to expand...

People who know about these things have worked out (and confirmed from experience) that for the majority of yachts the chain becomes nearly straight at about Force 6. If you want any shock absorbing effect above that, stretchy rope is the only way to get it. Nylon is stretchier than polyprop, I believe.

Pete
 
I guess it depends on whether you are planning on long-term or short-term use. Our anchor snubber is just a couple of metres long and "Y" shaped - there's a chain hook and two legs that we lash to the forward mooring cleats. But we only anchor short-term for lunch or an afternoon kip - the snubber is really just there to take the load off the windlass bearings. If you are planning on anchoring long-term and possibly in poor weather conditions, there may be an argument for a longer snubber with some intentional stretch.
 
parsifal said:
Why not attach the line to the samson-post, then pay out more chain until the line takes the strain?
Click to expand...

I always attach the hook with line and then let the anchor chain out until the line is under load and there is a loop of redundant chain. My question is whether to make the line off to a cleat at the bow or to a cleat amidships.

TudorSailor
 
tudorsailor said:
I always attach the hook with line and then let the anchor chain out until the line is under load and there is a loop of redundant chain. My question is whether to make the line off to a cleat at the bow or to a cleat amidships.
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Either would work, but you'll get more movement over the bow roller if the snubber line runs down the side deck. If the lead isn't perfect this would cause more chafe.

Pete
 
I can't see what's wrong with attaching to the bow cleat, as you do now, and just having a line as long as you want. All it means is that the hook will be that much further away from the boat, which is not going to be a problem. That's what I do, except I attach the line to the chain with a rolling hitch instead of a hook.
 
tudorsailor said:
I always attach the hook with line and then let the anchor chain out until the line is under load and there is a loop of redundant chain. My question is whether to make the line off to a cleat at the bow or to a cleat amidships.

TudorSailor
Click to expand...

No, the closer you can make-fast the snubber line to the edge of the boat the better. The line will move less and there will be much less chance of wearing through the line. Even so any part that touches your fairleads, etc will need substantial anti-chafe over quite a long distance in really strong winds. Even then, you will need to be able to veer it a couple of inches every hour or so in really heavy conditions.

You need to use three strand nylon and a minimum of about 20ft to be effective (more the better). Again don't make it too thick or the loads generated won't stretch the line by much - 12mm is the maximum up to about a 10 ton boat. This has a three ton breaking strain, but the loads on your anchor will be fraction of that. Ten millimetre would do easily, but chafe a bigger issue.
 
And it depends on where you are going to sleep. If it goes to the midships cleat there will be more likely hood of it rubbing on the side of the boat especially in light winds. I always find that noises get louder the closer you are to nodding off! If you have a reasonably raked bow then, even in light airs, it will drop down vertically and clear of the hull.
 
My snubber is 12 mm nylon doublebraid, used with 8 mm chain. Under most conditions I let out 2 - 3 metres after attaching the hook to the chain. As conditions worsen the stretch in the snubber becomes quite obvious, upon which I usually transfer the fixed end to the midships cleats, adding a further 4 - 5 metres or so. Simply letting more out runs the risk that the weight of chain will not be acting downwards on the hook, upon which it could detach.
 
We use a chain hook and run the snubber from the aft cleats, giving us about 12m of snubber. We are currently trying 11mm climbing rope, it is built specifically to be elastic. We use hose pipe on areas of wear. Rubber snubbers are a waste of time and money, they are lovely and stretchy but reach their maximum elongation under low loads, so just when you need them they become useless, whereas nylon is elastic almost until it fails, say 2t. We ran a test on 8mm chain, in air, 30m at a 5:1 scope. All the chain was off the ground at an 80kg load, so maybe 70kg in water - this is the load generated at under 20 knots. Any frictional advantage of your chain has then disappeared and any gust will generate sufficient momentum for you to enjoy a snatch load, chain is pretty inelastic so that snatch is on the anchor and whatever the chain is attached to on your yacht - nylon gives elasticity (but there is little give in 2m of nylon) - go for as long as you can. If you have a beamy yacht, we have a cat - then have 2 snubbers, one down each sidedeck (we run ours, 12m each side, through turning blocks on the bow). When all deployed we have enough slack chain to more than compensate for the elasticity and this slack, being heavyish, ensures the chain hook does not fall off when winds are light.

Jonathan
 
tudorsailor said:
I always attach the hook with line and then let the anchor chain out until the line is under load and there is a loop of redundant chain. My question is whether to make the line off to a cleat at the bow or to a cleat amidships. TudorSailor
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Over the bow. Let enough out so if you're riding the anchor with wind over tide the rope (not the chain) is hard against the topsides.
 
Neeves said:
We use a chain hook and run the snubber from the aft cleats, giving us about 12m of snubber. We are currently trying 11mm climbing rope, it is built specifically to be elastic. We use hose pipe on areas of wear. Rubber snubbers are a waste of time and money, they are lovely and stretchy but reach their maximum elongation under low loads, so just when you need them they become useless, whereas nylon is elastic almost until it fails, say 2t. We ran a test on 8mm chain, in air, 30m at a 5:1 scope. All the chain was off the ground at an 80kg load, so maybe 70kg in water - this is the load generated at under 20 knots. Any frictional advantage of your chain has then disappeared and any gust will generate sufficient momentum for you to enjoy a snatch load, chain is pretty inelastic so that snatch is on the anchor and whatever the chain is attached to on your yacht - nylon gives elasticity (but there is little give in 2m of nylon) - go for as long as you can. If you have a beamy yacht, we have a cat - then have 2 snubbers, one down each sidedeck (we run ours, 12m each side, through turning blocks on the bow). When all deployed we have enough slack chain to more than compensate for the elasticity and this slack, being heavyish, ensures the chain hook does not fall off when winds are light.

Jonathan
Click to expand...

In the Med we have noticed a profound difference in the behaviour of boats at anchor between those on 10mm chain and those on 8mm. 10mm is clearly superior. Out here there is no substitute for scope wind can rise from nothing to 50 kts in a couple of minutes without warning, then it goes away just as quickly, at 6:1 scope it takes a 40KT wind to to pull 10mm chain straight with a 12 ton boat, the snubber we use is a simple chain hook and 20mtrs of 12mm nylon which is passed over the second bow roller and made off to a cleat. At 50kts of wind (if its set to blow all night) we put a piece of pipe over the snubber line to protect from chaff on the cheeks of the bow roller, up till then its not an issue. ANYTHING for a quiet night! if you call 50kts of wind howling around quiet.

Some skippers out here have a big shackle and attach it to a spare anchor and pay this out over the anchor chain (so the shackle is over not through the chain so it can slide along the chain, the line is attached to the spare anchor so it can be restrained half way down the scope). They are using the spare anchor as an angel. This seems to work well when chain is undersized.
 
Where do I find the figures that you quote for how much wind it takes to pull the chain straight? My yacht is 20tons and the chain is 12mm. So how much wind would it take to straighten the chain. I too am anchoring in the Med - The Adriatic this season where the Bora can blow with gusto apparently.

TudorSailor
 
tudorsailor said:
I always attach the hook with line and then let the anchor chain out until the line is under load and there is a loop of redundant chain. My question is whether to make the line off to a cleat at the bow or to a cleat amidships.

TudorSailor
Click to expand...

This site suggests taking it to a cleat at the bow...

http://www.muir.com.au/accessories/pleasure-accessories/dock-and-anchor-line/snubber-line-kits.html

...surely something that can be knocked up without needing a spliced hook.

The Rocna website recommends tying a warp to the chain using "a rolling hitch plus loose clove hitch (or two) to secure the working end". Also at the bow:

http://www.rocna.com/kb/Snubbers

No need to go back to a midships cleat looking at their advice...

Andy
 
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tudorsailor said:
This gets more interesting still

This site clearly states that a long snubber is recommended http://www.morganscloud.com/2010/07/22/anchor-rode-snubbers/

They have a link to a "thesis" on anchoring with spreadsheets to calculate load. Fascinating http://alain.fraysse.free.fr/sail/rode/forces/forces.htm

TudorSailor
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Hmmm, good article. I like the suggestion made in the comments of using a double rolling hitch tied off with a couple of half-turns rather than a hook - the author said they replaced their heavy-duty hook with one that had a spring-loaded clip to prevent it falling off. "It should do" they said. Call me old fashioned, but I prefer to take any element of 'should' out of any kind of engineering solution.

To summarise the article: only a long snubber can absorb shock and take the load off the windlass. Fair point, well made.

Andy
 
Another reason I would avoid having lines running down the side decks is that I might forget they are there when I'm making my pyjama-clad, bleary-eyed way forward in the middle of the night to relight the anchor lamp. There's enough trip hazards on a yacht's deck without adding more. :)
 
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