Anchor fail

[Neeves]

Thanks Dom for the clarification, I'm surprised (and glad to be educated and my ideas found wanting). Its good to learn ones assumptions are wrong. Like Greeny I'd like to see some data. In the absence of data - I will be more cautious.

I'd add - my whole idea of using a decent snubber is to reduce the shock loads. Others, and sadly many, simply use a snubber to take the tension off the windlass which is admirable - but a short piece of rope will protect the windlass but do nothing else. A long, and importantly, elastic, think nylon (better dynamic climbing rope) will offer protection to the windlass and will tame shock loads. If you are taming shock loads the reduction in strength (say 25% - so now our chosen rode of 14mm anchor plait has a UTS of 3t (not the 4t specified) and the WLL has reduced from 1t to 750kg is not a major issue - because if you have removed the shock loads (they are taken within the snubber) then they will be a few 100kg (at most) and no-where near the 750kg 'limit'. I am assuming (sorry I keep making assumptions ) the use of the rolling hitch only produces a temporary loss in strength and that it is not permanent.

This raises another issue - you should not use a long elastic snubber alone, by itself (perfectly happy if you are alone but much more fun if there are tow of you ). The snubber needs a back up - some form of chain lock (we use a short dyneema strop and a chain hook, if it were a mixed rode then another rolling hitch is needed attached to a strong point). Snubbers are consumables, like sails or anchor chain - it will wear out and if you do not replace frequently/occasionally it will fail with a sound like gunshot (so you will not miss the failure). You don't wan the tension suddenly transferred to the windlass - so use a back up.

But returning to the deleterious impact of the rolling hitch (and prussic knot) there needs to be another idea for attaching a snubber to a mixed rode. As though I minimise the dangers I'm all for maintaining the integrity of any item of equipment.

I'm also keen to see the data.

Jonathan

 

[Neeves]

Returning to the theme of the thread and the additional data, the photograph of the location, that Zoidberg has provided it would be interesting the learn of the thought process of the owner of the yacht. He knew bad weather was forecast yet he appears to have anchored facing the brunt of the weather and the seas that I assume (again) would develop. Snubbers might not have been much use, simply delaying the inevitable - as if the rode had not failed - the anchor might well have been plucked out.

A completely different facet - our insurance premiums increases if the insurance companies face higher than expected (or normal losses). If the yacht had been lost we would inevitably have been paying for the settlement paid to the owner.

???

Jonathan

 

[JumbleDuck]

All this depends on there being shock loads to start with. Since nobody worried about this stuff twenty years ago, it's either largely imaginary (an option I am not dismissing) or its related to changes in boat design. The impression I get is that the problem is generally reported by people with modern boats (plumb stems and flat underwater sections) or catamarans, and I suspect that these behave very differently from older designs. If my boat (long keel, curved stem) pulls back against her chain she jsut dips her bows slightly and comes to a gentle stop.

 

[zoidberg]

Returning to the theme of the thread and the additional data, the photograph of the location, that Zoidberg has provided it would be interesting the learn of the thought process of the owner of the yacht. He knew bad weather was forecast yet he appears to have anchored facing the brunt of the weather and the seas

A completely different facet - our insurance premiums increases if the insurance companies face higher than expected (or normal losses). If the yacht had been lost we would inevitably have been paying for the settlement paid to the owner.

I continue to wonder WHY the fellow sailed close past the entrance to Newlyn harbour, anchoring less than half-a-mile away on a leeshore. Had he intended to enter Penzance, also close nearby, but needed to await its opening, then there's a charted anchorage just outside.

Could it possibly be that he was uninsured, and that Newlyn's harbour entry form ( online ) indicates BOLDLY that they will require sight of the vessel's insurance schedule? Yes, it's speculation....

 

[TernVI]

Mariners have been anchoring for many centuries. I seem to recall that St Paul was wrecked on a leeshore after his boat's anchor failed to hold....
I read these tales, ancient and modern, and ask myself what knowledge/understanding/seacraft I can glean from them - for my own benefit.

One thing was evident, from a superficial peek at the site if this latest Penzance stranding.... the 'perp' helpfully anchored in line of sight from the Newlyn Harbour Office window, so the lifeboat crews didn't have far to go.

Would scarcely have got the engines warm.....

In the event, the beach got to the boat quicker.

A GPS anchor alarm might have come in handy. But possibly, by the time the boat moved enough to trigger that, it was in conditions where motoring to safety might be difficult?

 

[Neeves]

All this depends on there being shock loads to start with. Since nobody worried about this stuff twenty years ago, it's either largely imaginary (an option I am not dismissing) or its related to changes in boat design. The impression I get is that the problem is generally reported by people with modern boats (plumb stems and flat underwater sections) or catamarans, and I suspect that these behave very differently from older designs. If my boat (long keel, curved stem) pulls back against her chain she jsut dips her bows slightly and comes to a gentle stop.

JD - you may be correct that the need for a snubber, or snubbers (a bridle) is a result of modern yacht designs. The fact that your yacht does not yaw, does not horse (because, you deduce, it is of a 'traditional' design) and you are never subject to bullets coming from variable directions in an anchorage is no reason to reject the need, for snubber(s). I can also assure you that a number of the members here, some of whom sail more traditional designs, do you use snubbers (in their elastic form) and you can thus focus your imagination in another direction . I can also confirm that some with traditional designs do not feel the need for snubbers - but then some carry excessive kilograms of chain that would be anathema to those with plastic fantastics. No-one has ever said everyone should use a snubber, fortunately the choice is that of the owner.

You must have noticed that the purveyors of new yachts, Bennys, Jennys and Hanses etc do seem to conduct reasonable business - partially because there are not enough of the traditional design's available (and people are time poor). There are thus a rather large number of AWBs possible more than those of a more traditional build - you might actually be well outnumbered (you would be here - in the lucky country).

So no reason to reject an answer to a problem - just because it is unknown to you.

Jonathan

 

[dom]

Thanks Dom for the clarification, I'm surprised (and glad to be educated and my ideas found wanting). Its good to learn ones assumptions are wrong. Like Greeny I'd like to see some data. In the absence of data - I will be more cautious.

@ Neeves (many great points as ever ) & @greeny : entirely sensible to ask for data here but I'm not sure there is any, for the reason that a Prusik or rolling hitch type knot will generally be expected to fail before the line to which it is attached. The relevance in this case is that dynamic climbing rope of around 10.5mm will typically have an ultimate strength of around 2.5-3 tons and 12.5mm up to around 5 tons. So that is close enough to the kind of anchor rodes we are talking about here to raise the question.

However, we do know that the radius of the turn is crucial with rope strength, and for 10-18 mm ropes 10cm is the normal minimum radius before any strength loss occurs. The effect isn't linear so a cleat with a much tighter radius than 10cm will be much much better than a really sharp bend in a knot. When I asked a chap from Marlow about this he pointed out that a rolling hitch is designed to twist the line to which it is attached through a sharp turn of about 90 degrees and one can see this in practice. The first link below provides data with similar radius turns in which light the 25% seems pretty conservative.

The aforementioned Prusik knots are also interesting in that most assume their strength to be about twice the rated strength of the cord used to tie one. Which makes intuitive sense in that the loop has two ends. Except that's wrong, it's only about the strength of the line itself, second reference (second link).

Finally re rope rodes: ask any climber and they will wax lyrical about rope maintenance. For rope is not like chain which, if it doesn't look manky, will probably be fine. Leave a salt laden rope in a wet anchor locker for years where it is rarely/never inspected for chafe/damage and where little/no regard is given to its age/use one can expect it to fail FAR below its ratings. Unlike chain, rope rodes often fail, so one should make sure to implement a proper maintenance schedule. Neeves and others points about avoiding chafe are also hugely important, as may turn out to be the case with the unfortunate grounding in question.

Knot Break Strength vs. Rope Break Strength

http://itrsonline.org/wordpress/wp-content/uploads/2015/02/004.Evans_.2014.pdf

 

[JumbleDuck]

JD - you may be correct that the need for a snubber, or snubbers (a bridle) is a result of modern yacht designs. The fact that your yacht does not yaw, does not horse (because, you deduce, it is of a 'traditional' design) and you are never subject to bullets coming from variable directions in an anchorage is no reason to reject the need, for snubber(s).

"Horse"? My boats yaws around like anything, thanks to high bows, but at the end of each swoop she comes to a graceful and gradual stop before heading back the other way. No hint of a jerk (I'll let someone else make the joke).

On that basis, no, I don't need a snubber. I do have a short length of rope with a chain hook on it which I use through a fairlead to pull the chain to one side of the bow roller to stop it banging across and back during the swoops.

I can also assure you that a number of the members here, some of whom sail more traditional designs, do you use snubbers (in their elastic form) and you can thus focus your imagination in another direction .

People do all sorts of strange things.

You must have noticed that the purveyors of new yachts, Bennys, Jennys and Hanses etc do seem to conduct reasonable business - partially because there are not enough of the traditional design's available (and people are time poor). There are thus a rather large number of AWBs possible more than those of a more traditional build - you might actually be well outnumbered (you would be here - in the lucky country).

So no reason to reject an answer to a problem - just because it is unknown to you.

If people experience the problem then of course they should deal with it in an effective way. However, I think a lot of the discussion on snubbing here is based on unsupported anecdote and myth, and using them has become a bit of a fad. I have seen several boats recently religiously deploying long snubbers on lovely calm evenings. All good fun, I suppose.

 

[Neeves]

Could it possibly be that he was uninsured, and that Newlyn's harbour entry form ( online ) indicates BOLDLY that they will require sight of the vessel's insurance schedule? Yes, it's speculation....

We have a similar restriction here, though I have only heard of it applied to a marina - and in 20 years here have only been asked to produce the insurance certificate once.

But it does make me query - can you be refused entry in time of danger and potential loss of vessel/life? And how do they deal with you when its blowing 50 knots and teeming with rain after you have made the shelter of the safe haven...???

Jonathan

 

[greeny]

@ Neeves (many great points as ever ) & @greeny : entirely sensible to ask for data here but I'm not sure there is any, for the reason that a Prusik or rolling hitch type knot will generally be expected to fail before the line to which it is attached. The relevance in this case is that dynamic climbing rope of around 10.5mm will typically have an ultimate strength of around 2.5-3 tons and 12.5mm up to around 5 tons. So that is close enough to the kind of anchor rodes we are talking about here to raise the question.

So you're saying the prussic/rolling hitch on the snubber attachment will fail before the main anchor warp. That's what I thought. The failure is not the main line. Forget the question I'm getting confused, I'll carry on doing what I was shown to do.

 

[boomerangben]

Long snubbers make sense to me. It is then area under the force extension graph that absorbs the energy of the moving vessel. The longer the available stretch the more energy can be absorbed. Managing the practical issues of fibre rode components is obviously key.
But on a slightly different aspect, if a snubber is run down one side of the deck to a stern cleat, this sets up asymmetric forces on the bow roller and stern cleat. Depending on the vessel and geometry I imagine there is a tendency for the mooring system to increase yawing compared with a say mixed rode made off on a centreline Samson post. Is this significant?

 

[anoccasionalyachtsman]

Long snubbers make sense to me. It is then area under the force extension graph that absorbs the energy of the moving vessel. The longer the available stretch the more energy can be absorbed. Managing the practical issues of fibre rode components is obviously key.
But on a slightly different aspect, if a snubber is run down one side of the deck to a stern cleat, this sets up asymmetric forces on the bow roller and stern cleat. Depending on the vessel and geometry I imagine there is a tendency for the mooring system to increase yawing compared with a say mixed rode made off on a centreline Samson post. Is this significant?

The anchor doesn't know where the rope is cleated - it's arguing with the bow roller.

 

[boomerangben]

Long snubbers make sense to me. It is then area under the force extension graph that absorbs the energy of the moving vessel. The longer the available stretch the more energy can be absorbed. Managing the practical issues of fibre rode components is obviously key.
But on a slightly different aspect, if a snubber is run down one side of the deck to a stern cleat, this sets up asymmetric forces on the bow roller and stern cleat. Depending on the vessel and geometry

The anchor doesn't know where the rope is cleated - it's arguing with the bow roller.

But the anchor is (hopefully) nailed in the seabed and irrelevant to what is happening on deck. Even if the anchor, bow roller and the centreline of the vessel are in a straight line, cleating the rode off centre creates a tendency to yaw unless by chance all the forces resolve through the yaw axis.
The vessel knows exactly where the rode is secured to, exactly what wind and waves are causing it to move about and what direction the rode leaves the bow roller. The anchor just knows how hard the boat is pulling and where the bow roller is relative to it

 

[James_Calvert]

Interesting debate here.

I think the net horizontal force on the bow roller would counteract the effect of the off-centre cleating, maybe over compensate a bit.

Imagine towing a flat bottomed tender with the painter attached to a stern quarter passing through a ring on the top of its bow. I think the tender would align itself so the painter was straight.

 

[JumbleDuck]

But the anchor is (hopefully) nailed in the seabed and irrelevant to what is happening on deck. Even if the anchor, bow roller and the centreline of the vessel are in a straight line, cleating the rode off centre creates a tendency to yaw unless by chance all the forces resolve through the yaw axis

'Fraid not. Anoccasionalyachtsman and James_Calvert are quite right: once the rope has come through the bow roller it makes no difference where it's cleated. If you take it to a cleat on the quarter, the inward pull on that cleat will be exactly balanced by the outward force on the bowroller, and the moment produces by those two will be exactly balanced by the off-centre longitudinal force at the back.

 

[anoccasionalyachtsman]

Imagine towing a flat bottomed tender with the painter attached to a stern quarter passing through a ring on the top of its bow. I think the tender would align itself so the painter was straight.

Suppose that you set it up as you describe and let the dinghy take up its position of equilibrium. Now superglue the painter to the bow ring - if you're right then the dinghy will swing 'straight'.

Edit: to be more clear, glue the painter and then free it from the quarter fastening.

 

[Neeves]

A key to initiating the snubber at the transom is getting the snubber running through and from the bow roller in a straight line with a minimum chance of abrasion. It really depends on what you have available that you can use so that the snubber runs straight but a simple answer is a set up like a barber haul, a strop with a block from one toe rail with the length ensuring the snubber runs straight over the bow roller (you will still need to protect the snubber - the chain is also on the bow roller and the front of the bow roller will abrade the snubber as you yaw).

You can crudely define what the tensions are on your rode. You need to know the specification of your snubber but its extension will define what tension is imposed. If you speak to Marlow (who also make dynamic climbing rope), or any rope maker, they will be able to advise the specification omitted from public view.

I'd advocate you consider whether you can set up a bridle, a snubber from each transom horn cleat and then running outboard at the bow. As you have a deck length snubber the length outboard at the bow can be quite short allowing you to maximise the angle between the 2 snubbers which will help to reduce yawing. Having 2 snubbers will also prolong their life., again you need to watch for abrasion and the arrangement will depend on what is at the bow. One yacht with which I was involved we took the snubbers outboard at the amidship cleats but 'controlled the snubbers when outboard with LFRs on short strops, as you control spinnaker sheet/guy. It works and the yacht went up to Alaska, from Vancouver.

Most climbing ropes (or they are here) used in gyms are 12mm or near 12 mm which is a bit beefy for a 30' yacht. Sadly I haver not found gyms here using anything smaller which means that if you want to use climbing rope and it is available in sizes from 8mm to 12mm - then for smaller sizes you need to buy it, new. I'd guess if you know anyone who climbs or maybe tap into a rock climbing club or tree surgeons you might find an old thinner rope - and if it has been discarded by a climber he should make sure it is not going to be used for height safety - which might mean landfill or application on yacht!

12mm rope is a devil to knot, I initially used hayyard knots but having proven my system I invested in new ropes and had loops sewn on each end by the rope maker (a sail loft would do this for you). If you have a bigger yacht you might consider larger than 12mm (but I suspect as JD might suggest - larger cruising yachts don't move as friskily as smaller ones and have less need for snubbers) and I sourced 14mm ropes for a 50' cat (which definitely need sewn loops).

I have a pdf of our arrangement - no link. Happy to forward - but I need your email address.

We have 2 reasons to be fixated with snubbers/bridles - we have a cat which demands a bridle anyway. We went through the evolution where our bridles got longer and longer and incorporated those rubber dog bone things (waste of time and money) and we use lightweight chain and have thus sacrificed catenary. We saved money, weight and introduced another problem - which is now solved.

Our arrangement is to run from the transom to a turning block on each bow to LFRs incorporated in the centrae attachment position (a hook) on the chain and then back to the bow. This is about 15m each side. This is what we use 'everyday'. We have 30m available and if the wind gets up or we are anchored subject to swell from the Tasman Sea we can extend by simply deploying more snubber from each transom. Because we double back from the attachment point on the bow the amount extra forward we release is not that 15m but a fraction of it. Because we do most of the 'work' at the transom you really only need to visit the bow to move the back up chain hook.

We use 12mm ropes, 38' x 7t cat - windage of a 45' AWB - I think we should be using 10mm (I will try - and whether we notice the difference don't know.

JD has a point - there is some religious zealotry in all of this - and the subjective part is not 'does it work?' too many say yes it does - the unknown is the size of rope needed. People have tried to define rope size vs vessel size/type but all the data I see seems overly generous, too beefy, like our use of 12mm. there is probably a trade off between rope diameter and length - it needs a mathematician or - suck it and see.

Jonathan