Dragging of anchors

[Neeves]

We have a mark on our snubbers, at the turning block (this is at about 9m) and we can see how the snubbers stretch. If the wind is blowing, say, at 30 knots the snubbers are already stretched and unless you mark where zero is you do not know what the base line is - and the gusts might be 40 knots.

We do not use a buoy on a short line and have never had the need (but one day maybe). We would not consider our anchor 'set' unless it has disappeared (it has no roll bar) - and then of course if you have no datum you do not how disappeared it is! We mark (different colour cable ties) the chain closest to the anchor at 1m intervals from the shackle - then we know how much chain is buried. If we had a buoyed line I'd be marking the line as well so that I knew how deep the anchor was buried - though you can crudely work out the depth, of the shackle, using simple geometry.

Jonathan

edit - because the snubber absorbs all the shock loads (assuming the correct length of snubber) the chain hook does not actually need to be strong, it just needs to stay on and if the chain is in tension it should not fall off anyway. Modern fashion is for dyneema soft shackles (and as I mention we find them far too fiddly to attach to 8mm chain) instead of a chain hook. One reason is you can retrieve the chain over the bow roller and then disengage the soft shackle. The implication is that you need the strength of the dyneema - I suspect its not the strength that is needed but abrasion resistance. We are happy using a chain hook, a one handed operation. Of course if you have a very short snubber then the chain hook (or the soft shackle) takes a full snatch load and does need to be strong. - close edit

 

[vyv_cox]

We don't have a problem with the chain hook coming off as it doesn't touch the bottom. The chain hook is very strong and convenient to deploy and remove. I forgot to mention that the snubber line goes through blocks on its way to the bow roller and the line is protected from chafe as it goes over the roller with hose. All very easy to use and works well as it is. It has taken some time to perfect it

Much the same arrangement for us. The forged chain hook is good, has never come off unintentionally but falls off as soon as we begin to haul in chain. There has never been a time when we needed to detach the snubber in a big hurry but I think that a soft shackle might slow the procedure down a bit. Our snubber goes from the cleat to the second bow roller where I slide a short length of plastic tube to protect from chafe and reduce the transmitted noise in the forecabin. I do use a soft shackle to attach the anchor shackle to the boat when we are sailing, easier to set than the previous hard one.

 

[sailaboutvic]

We also don't use the dog bone any more,
We had three, all have broken at one time of another.

I was a little confused why Jonathan had an 14 mts bridal that's why I asked the question about size, but now having explained how he has it fitted, I can see why it's so long.

For us It will Depend on the depth of water we have anchored and what wind condition we are expecting, how much snubber we let out,
Our bow is about one point five meter above the water, so If we have four below us, we let out five , (3.5 in the water 1.5 above) on the other hand, if we are in 8 mts plus of water and we are expecting a blow than six or seven goes out,
What I don't want to do , is having it dragging on the bottom , in which case there a chance of the hook coming off the chain.
we fine this work for us on an 12 mts boat 9 tons, mind you with all the crap we have more like 11 tons.

Our snubber (bridle) comes up at the bow and goes through the fair leads on both sides of the bow and onto the cleats which I have reinforced some time back.
We use a hook because if we need to get it off quickly, we can, we don't want to mess about undoing a shackle, yes, it is possible for it to come off the chain, although we have only had it happen once.

Short snubber, seem to be very common, just sitting above the water, I guess all that would doing is taken the stress away from the windlass and not much else in a blow
Going back to what Riva said regarding an anchor stuck inside the hoop of a Rocna.
I can easily see how that would be possible.

 

[GHA]

Sorry that's new to me and I'm not sure I understand it. Any references?

The energy in a moving boat is = 1/2 x mass x velocity squared, and if you want to stop it the energy transfered will be force x displacement (which for us could probably safely be the same as distance over which the snubber stops the boat) . So with just chain in a gust, the catinary disappears over a very short distance and with force=mass x acceleration the force can be extremely high.

A slight ,err, drift ...

In my experience the anchor works hardest in strong gusty conditions where the boat gets blown around with big gusts from different directions . Energy is proportional to V squared so keeping the boat as slow as we can helps lots - has anyone tried a drogue off the bow to slow the boat down in nasty gusty weather? A riding sail has very good press to help as well.


(and, please, someone check those equations? ta)

 

[JumbleDuck]

Is the regular use of snubbers a new thing, perhaps because of modern lighter boats or perhaps because of modern stem designs? My boat is 26', long keeled and 4 tons, so she doesn't skite around much. When she does blow back in a gust, she does so fairly sedately and when the chain gets taut she dips her bow gently - the curved stem seems to provide a hydrostatic spring as it dips in. Maybe lower displacement ratio boats blow back faster and then vertical stems provide less bounce?

Note: I'm not arguing with anyone who snubs, but I'm curious as to why snubbers seem to be more of A Thing now than they were twenty years ago.

 

[geem]

Is the regular use of snubbers a new thing, perhaps because of modern lighter boats or perhaps because of modern stem designs? My boat is 26', long keeled and 4 tons, so she doesn't skite around much. When she does blow back in a gust, she does so fairly sedately and when the chain gets taut she dips her bow gently - the curved stem seems to provide a hydrostatic spring as it dips in. Maybe lower displacement ratio boats blow back faster and then vertical stems provide less bounce?

Note: I'm not arguing with anyone who snubs, but I'm curious as to why snubbers seem to be more of A Thing now than they were twenty years ago.

I have been using snubbers for more than 20 years. Certainly not new to me

 

[JumbleDuck]

I have been using snubbers for more than 20 years. Certainly not new to me

I'm sure they are not new, but there seems to be a lot more discussion of them now, hence my "...regular use..." in the previous post.

The only problem I get during windy conditions at anchor is the boat yawing and then sailing across the wind and back. That itself is not the issue, and boats of all designs seem to do it, but every time she changes direction the chain bangs across the bow roller, which is a bit noisy. I normally tie the chain to one side, or put it through a fairlead instead of over the roller.

 

[Neeves]

The energy in a moving boat is = 1/2 x mass x velocity squared, and if you want to stop it the energy transfered will be force x displacement (which for us could probably safely be the same as distance over which the snubber stops the boat) . So with just chain in a gust, the catinary disappears over a very short distance and with force=mass x acceleration the force can be extremely high.

(and, please, someone check those equations? ta)

The formula is correct, 0.5 x Mass x Velocity squared.

The formula answers JD - its velocity squared - so a skittish yacht develops more energy because it yaws quickly.

Modern yachts have high windage (big hulls with lots of accommodation), are light, but low wetted surface area and fin keels - and tend to be skittish compared to heavier, more squat, hulls, high underwater accommodation, with long keels. As yachts have tended to toward increased skittishness there has been a need to counter the resultant increase in snatch loads at anchor. Adding chain weight either longer or bigger diam is one answer - but there is a limit - hence the 'recent' interest in elastic snubbers.

It is possible to calculate the energy absorbing characteristics of nylon cordage. By calculating the energy of the moving yacht you can define exactly what size and length of snubber you need.

One big unknown - what would be a good and sensible figure for the velocity of a yacht yawing at anchor? 1 knot, 2m/sec??

Snubbers have been mentioned for decades - but only short things, - to take the load off the windlass (edit - and to stop the chain rattling on the bow roller - close edit). Original use of snubbers mentioned samson posts - but they have gone the way of long keels!

We are at a point of transition between the catenarists and the minimalists. As you point out - not long ago (elastic) snubbers were simply not mentioned, similarly high tensile chain was not mentioned.

And returning to the thread - 10-15 years ago, having an anchor drag was not unusual now....

Jonathan

 

[geem]

I'm sure they are not new, but there seems to be a lot more discussion of them now, hence my "...regular use..." in the previous post.

The only problem I get during windy conditions at anchor is the boat yawing and then sailing across the wind and back. That itself is not the issue, and boats of all designs seem to do it, but every time she changes direction the chain bangs across the bow roller, which is a bit noisy. I normally tie the chain to one side, or put it through a fairlead instead of over the roller.

Being a ketch we have additional windage at the back of the boat that acts like the tail fin on a plane. It keeps us pointing into the wind and we don't sail around our anchor so much. Gusts from different directions when anchored is where the long snubber really comes into its own. It vastly reduces snatch and we get no noise at all from the chain as it just hangs in a large bight below the snubber. Lots of love aboards have cured the yawing around at anchor without realizing. They have added so much kit to the back of the boat such as arches, solar panels, wind turbines, antenna, etc that it acts like my mizzen mast and keep them head to wind at anchor....

 

[Neeves]

A slight ,err, drift ...

In my experience the anchor works hardest in strong gusty conditions where the boat gets blown around with big gusts from different directions . Energy is proportional to V squared so keeping the boat as slow as we can helps lots - has anyone tried a drogue off the bow to slow the boat down in nasty gusty weather? A riding sail has very good press to help as well/QUOTE]

The RN used to advocate dropping a second anchor so that it simply scraped across the seabed - a sort of friction brake.

I'd wondered about a bucket, as i do not have a drogue of the size or strength needed - but never tried it.

Jonathan

 

[Neeves]

Being a ketch we have additional windage at the back of the boat that acts like the tail fin on a plane. It keeps us pointing into the wind and we don't sail around our anchor so much. Gusts from different directions when anchored is where the long snubber really comes into its own. It vastly reduces snatch and we get no noise at all from the chain as it just hangs in a large bight below the snubber. Lots of love aboards have cured the yawing around at anchor without realizing. They have added so much kit to the back of the boat such as arches, solar panels, wind turbines, antenna, etc that it acts like my mizzen mast and keep them head to wind at anchor....

There is a danger of increasing the population - an unanticipated side effect perhaps.

 

[JumbleDuck]

We are at a point of transition between the catenarists and the minimalists. As you point out - not long ago (elastic) snubbers were simply not mentioned, similarly high tensile chain was not mentioned.

Given that (a) modern anchors will happily attach a battleship to a pot of meat paste (OK, maybe a slight exaggeration) and (b) springy nylon snubbers are A Good Thing with modern boats, what's the point of using chain at all, except perhaps a wee bit at the anchor for abrasion resistance? My Hunter 490 has 20m of braided nylon, 2m of chain and a claw, and it gives a very comfortable ride.

 

[NormanS]

The energy in a moving boat is = 1/2 x mass x velocity squared, and if you want to stop it the energy transfered will be force x displacement (which for us could probably safely be the same as distance over which the snubber stops the boat) . So with just chain in a gust, the catinary disappears over a very short distance and with force=mass x acceleration the force can be extremely high.


(and, please, someone check those equations? ta)

Oh dear! Anchoring used to be so much simpler before we had to worry about all these formulae.

 

[Neeves]

JD

Coral eats nylon overnight?

Lots of people use mixed rodes its not really unusual. If you use a mixed rode you do not need a snubber (though you might want a bridle (depends if your yacht is beamy).

Jonathan

 

[geem]

There is a danger of increasing the population - an unanticipated side effect perhaps.

nothing wrong with love...

 

[JumbleDuck]

Coral eats nylon overnight?

Lots of people use mixed rodes its not really unusual.

Not much coral here, although clearly an issue where it is.

 

[Neeves]

Not much coral here, although clearly an issue where it is.

Maybe not enough nylon in their diet perhaps?

Not actually much coral here, Sydney, but because The Reef is such an attraction and every yacht will go, or has ambitions to go, the standard rode is chain. But I am sure round you - lots of mixed rodes, quite normal - and they do not worry about catenary.

Jonathan

 

[lw395]

...

Snubbers have been mentioned for decades - but only short things, - to take the load off the windlass (edit - and to stop the chain rattling on the bow roller - close edit). Original use of snubbers mentioned samson posts - but they have gone the way of long keels!

We are at a point of transition between the catenarists and the minimalists. As you point out - not long ago (elastic) snubbers were simply not mentioned, similarly high tensile chain was not mentioned.

And returning to the thread - 10-15 years ago, having an anchor drag was not unusual now....

Jonathan

When I did my YM theory, just over 30 years ago, 3x scope was plenty and a CQR was something to covet.

I guess in those days there were better anchorages (not filled with moorings) and the season consisted of July and August?

Actually I think the theory was mostly cribbed from RN practice with battleships, yachts just chucked out more string until it stopped dragging?

 

[Delfin]

JD

Coral eats nylon overnight?

Lots of people use mixed rodes its not really unusual. If you use a mixed rode you do not need a snubber (though you might want a bridle (depends if your yacht is beamy).

Jonathan

I would add that in crowded anchorages I would rather be near all chain anchored boats than one with rode out because of the increased wandering around on the rode. Advantage for your neighbors, if not yourself perhaps..

 

[JumbleDuck]

When I did my YM theory, just over 30 years ago, 3x scope was plenty and a CQR was something to covet.

I guess in those days there were better anchorages (not filled with moorings) and the season consisted of July and August?

Perhaps it's modern lighter boats surging around faster and imposing bigger shock loadings on anchors which has driven the adoption of both modern anchors and snubbers?

Isn't 3x scope still plenty, with chain?