Anchor snubber design.

[Neeves]

I agree with what you say Jonathan, except the last statement. Seems to me it's about force not energy, and once the elastic stop stretching the force the boat the boat's reverse power applies to one end of the anchor snubber is the force being transmitted to the anchor at the other end. The elastic smooths out transient peaks in that force, but doesn't stop your engine pulling the anchor with all the force it would do with simply a length of chain. The result is that having a snubber in situ while power setting doesn't inhibit the set.

I agree with everything else you say.

I've watched people set with a snubber - what happens is that the energy of the moving yacht (the power of the engine) drive the yacht back. As the yacht is going backward it develops more energy than the engine is providing (it develops momentum) so the engine is providing X and the momentum is developing Y - this is transferred in total to the snubber, the energy in the snubber increases (X + Y) until it is larger than the energy provided by the engine and at some point the yacht stops moving back ward and the energy in the nylon (X + Y), now being greater than anything the engine (X) is offering pulls the boat forward., you can set up a yo-yo effect.

If your clutch on the windlass is set just right, the chain slips out.

Yes, X + Y will be higher than anything the engine can produce - but it is very temporary. I believe you are better to simply sit on reverse at whatever revs you choose and drive the anchor in a sustained manner. You can hold those revs for as long as you want.

Roughly a 10hp engine will develop about 100kg of tension at about 5:1 with a reasonably efficient prop.

Now someone will come along and shoot me down - or even better describe this with perfect physics.

You need, with my scenario, to have a chain lock - get the load off the windlass, massage (or father/mother) those seals.

Jonathan

 

[Neeves]

John Knox suggested setting using momentum because it gives you more force, power (whatever). I'm a bit twitchy about the idea of having a, say, 14t yacht reversing up at ?? 2 knots. Its very uncontrollable, considering you are reversing up and you will have a variable wind adding to what ever you do.

I prefer the sustained application of tension (with a chain lock).

I'm not that fussed about applying huge tensions - we just want to know the anchor has set, that its not caught something untoward in the toe. In most seabeds that is sufficient and the wind will do the rest (and if the wind is insufficient then power setting at max revs for 3 minutes was a complete waste of time).

In thin mud or weed we would be a bit more careful and take bit more time. We would try to avoid dense weed but needs must and. also with thin mud, its a suck it and see - until you are confident you have real hold.

Jonathan

 

[Neeves]

if you check this video

https://www.youtube.com/watch?v=-Q7-alugXMQ

You will note, after 2 minutes, that when maximum revs are defined (2,000rpm), and tension 'held' the snubber stretches and the chain pulls out. If the chain is releasing then the power being developed by the engine is continuing to reverse the yacht - and if the yacht is moving the anchor is not setting more deeply. So - the engine is holding the anchor AND allowing the yacht to move back, the engine revs are not focussed at the anchor but the yacht - if the chain were secured (not retained by a piece of elastic) possibly the anchor would be set more deeply.

Great video.

Jonathan

 

[BelleSerene]

- and if the yacht is moving the anchor is not setting more deeply.

Really? When does the anchor set then?

 

[Neeves]

The slippage of the chain occurred in mid-setting sequence. If the yacht is moving appreciably and the chain slipping out then the anchor is not setting more deeply (or not much). You can see in the video the chain moving out, which means the yacht is moving back (and possibly the anchor completely stationary). A good anchor sets and completes setting in a shank length - so the maximum a yacht will move backwards, for a good anchor is a shank length and depends on the yacht/anchor that is less than a metre - and I doubt you can 'see' that as your only reference point (if you are lucky) is the seabed and its too far away to judge less than a metre.

The mechanism to determine if your anchor is set is that the yacht remains stationary - as far as you can tell. If the chain is slipping you simply do not know. You can also 'feel' if the anchor is moving by touching the chain - if the anchor is moving the chain will 'rattle or tremble'

The video is being purported as way to set an anchor - I think it wrong. You want a solid connection between engine and anchor, so yacht and chain and chain attached to a strong point. That way the engine impact directly on the anchor. If the chain remains taut, is not slipping and you cannot detect movement (at whatever revs you choose) then the anchor is set. If with your chosen revs the chain is slipping out - you simply do not know. Equally if you are using a snubber and the snubber is take the tension you cannot 'feel' whether the chain it 'rattling or trembling' - it will become lost in a long snubber (that's one of the characteristics of cordage). If you want to know what your anchor is doing touch a taut piece of steel, call it a chain. If you use a chain lock or short dyneema snubber with chain hook but hook attached on deck you can still feel the chain at the bow roller.

As I say I think the technique wrong and sending the wrong messages - and it illustrates why.

Jonathan

 

[thinwater]

The slippage of the chain occurred in mid-setting sequence. If the yacht is moving appreciably and the chain slipping out then the anchor is not setting more deeply (or not much). You can see in the video the chain moving out, which means the yacht is moving back (and possibly the anchor completely stationary). A good anchor sets and completes setting in a shank length - so the maximum a yacht will move backwards, for a good anchor is a shank length and depends on the yacht/anchor that is less than a metre - and I doubt you can 'see' that as your only reference point (if you are lucky) is the seabed and its too far away to judge less than a metre.

The mechanism to determine if your anchor is set is that the yacht remains stationary - as far as you can tell. If the chain is slipping you simply do not know. You can also 'feel' if the anchor is moving by touching the chain - if the anchor is moving the chain will 'rattle or tremble'

The video is being purported as way to set an anchor - I think it wrong. You want a solid connection between engine and anchor, so yacht and chain and chain attached to a strong point. That way the engine impact directly on the anchor. If the chain remains taut, is not slipping and you cannot detect movement (at whatever revs you choose) then the anchor is set. If with your chosen revs the chain is slipping out - you simply do not know. Equally if you are using a snubber and the snubber is take the tension you cannot 'feel' whether the chain it 'rattling or trembling' - it will become lost in a long snubber (that's one of the characteristics of cordage). If you want to know what your anchor is doing touch a taut piece of steel, call it a chain. If you use a chain lock or short dyneema snubber with chain hook but hook attached on deck you can still feel the chain at the bow roller.

As I say I think the technique wrong and sending the wrong messages - and it illustrates why.

Jonathan

This is generally true for the best, fine sand.

In soft mud, as you know, setting can take >10 feet and pull the anchor 2-3 feet under ground. The "feel" from the chain is muted at best, and the boat will move up to 15-20 feet, as the anchor sets, the chain lifts, and the snubber stretches out. What is important in soft mud is that after this set and stretch, then movement stops. Proper setting method maters even more in soft mud, since the anchor has less ability to self right, and snagging on junk during a long set is more likely. It is a very gentle process, often requiring a 15 minute rest after the first very light set.

 

[Neeves]

This is generally true for the best, fine sand.

In soft mud, as you know, setting can take >10 feet and pull the anchor 2-3 feet under ground. The "feel" from the chain is muted at best, and the boat will move up to 15-20 feet, as the anchor sets, the chain lifts, and the snubber stretches out. What is important in soft mud is that after this set and stretch, then movement stops. Proper setting method maters even more in soft mud, since the anchor has less ability to self right, and snagging on junk during a long set is more likely. It is a very gentle process, often requiring a 15 minute rest after the first very light set.

All very true.

In mud you need to plan to have sufficient room behind you to allow for that settling distance - unlike sand where you can expect most, or all, 'good' anchors to set within shank length. Some anchor makers claim their anchors set very quickly (and more quickly than others) - to us a shank length is good enough.

And if you want any reassurance of hold you really need to use a Fortress in light mud - its the only anchor with which you can have any confidence (been there, done that). Forget the mantra that one anchor suits all - anchors are a compromise - there is no perfect anchor! Be prepared to alter your anchor to suit the seabed (or: go somewhere else or have a restricted sailing area).

We anchored in thin mud, well in fact we did not anchor initially, to sit out a Storm (well sheltered and well inland, just off the entrance to the Gordon River down the west coast of Tassie). We tried our Excel, tried our Spade and then the Fortress (this was before we had seen the Chesapeake mud test results on the Fortress website). Only the Fortress offered hold. Loki an older, but lovely, Swan (about 46') came alongside us once we had settled down and they tried their CQR, 5 times, without success (lots of mud over the foredeck). They eventually went close to shore and tied to trees (and still deployed the CQR). I know it is said you can deploy your anchor and leave it too settle and soak and that this 'setting period' will allow an anchor to develop hold. I simply do not have the patience - I want certainty now, not in 4 hours time (when in any case it still might not have set).

The man who REALLY makes the perfect anchor will clean up.

Jonathan

 

[noelex]

The video of using a snubber to set the Mantus anchor was made by wife and I several years ago.

Ideally, anchors like a gradually increasing force to set well. If you apply too much force to an anchor that is unset and just lying on the bottom, there is a risk it will skid along the bottom and not dig in. Once the anchor has started to dig in it will tolerate more force and dig a little deeper. Once it has buried more, it will tolerate greater force, and so on.

Having said the above, modern anchors are very forgiving. Give them a half decent substrate and they will tolerate a lot of abuse and still set well, but it still worth trying to give the anchor an easy time, especially in weed.

All the snubber does is even out the force, which facilitates a gradual increase in force, especially if there is wave action. With a modern anchor I don't have any any objection to setting the anchor without a snubber, but you will need some means of removing the load from the windlass (there are other ways of doing this) and more annoyingly if you want to set at full scope you will need to retrieve some chain, attach the snubber and then let out the chain again, which is a bit of pain especially with a 10m snubber deployed from the bow.

I believe in simple fuss free anchoring. It really does not have to be too complicated.

If you want to see what happens at the anchor end, I made this video at much the same time. it is not the same set (this one is only 3:1 ) but you can see the nice smooth progressive bury of the anchor, without any jerks or snatches. This is exactly the effect you are looking for.

https://m.youtube.com/watch?v=LDC0g1GzdUc

 

[Neeves]

Yes,

Its also an interesting video. Sand as soft as icing sugar.

You will note that the shank end, the shackle, never really engages with the seabed, so the chain never 'disappears'. You will also notice that the shank tends toward becoming parallel with the seabed. So the fluke starts off at a sharp seabed fluke angle and slowly flattens out to 16 degrees to the seabed. If you check a drawing of a Mantus - if the shank is horizontal the fluke is at 30 degrees. This low angle appears to occur at whatever scope ratio is being used

If you look at other anchors when they are 'well set' and evaluate the fluke angle, to the seabed, you will find it to be around 16 degrees, plus or minus 5 degrees.

As anchors dive more deeply the angle further decreases. Shallow angled fluke/seabed angles return low holding capacity.

The peculiarity, the uniqueness (the only anchor I know to show this characteristic), of the Mantus with its 16 degree fluke to seabed angle is common - virtually every underwater image of a Mantus shows the shank at 16 degrees.

Now - if you have a grossly oversize anchor it does not matter - the effective area compensates for the shallow angle. Basically you are lugging around a mobile mooring. Additionally Mantus does set quickly, even if not 'well' and a well set Delta or Bruce will hold well - so well and good - the Mantus is simply inefficient in modern terms.

I have to winder why Mantus have never conducted any independently verifiable holding capacity tests.

Jonathan

 

[noelex]

Jonathan, I have seen a lot of anchors underwater and the performance from the Mantus in that video is superb. I am not sure why you cannot see this, but with both the photos and videos I produce I do encourage people to make up their own mind.

Note there was nothing special about this set, although conditions were not ideal with a scope of only 3:1 in 4.4m of water. I only filmed the one set.

I have to winder why Mantus have never conducted any independently verifiable holding capacity tests.

Personally, I think the anchor "tests" paid for and organised by the manufacturer are of limited value. The anchor manufacturer controls alł the variables, analyses the results, and invariably wins the comparison. Surprise surprise.

 

[Neeves]

I see an anchor with its fluke at 16 degrees to the seabed.

I see images of Rocna, Spade, Excel, set without particular care a nd precision and they show 2 things - a shank with the shackle end, and chain buried, and a fluke at 30 degrees. A fluke at 30 degrees to the seabed has twice the effective surface area as one at 16 degrees (for the same sized fluke). Its simply geometry.

A previous quote by Noelex

Modern anchors bury the end of the shank where the chain is attached very early in the setting process. Any bulk of the chain connection will impede the anchor's ability to bury.*

end quote.

It was encouraging to see Noelex making this quote as it has been made by Practical Sailor for about 5 years now based on observation of how modern anchors actually work (which is toe and shackle end engage almost simultaneously and then bury together dragging chain with them). If you take any modern anchor then if the shackle end and toe bury together - the fluke is at 30 degrees.

Jonathan

 

[Flica]

Yes,

Its also an interesting video. Sand as soft as icing sugar.

You will note that the shank end, the shackle, never really engages with the seabed, so the chain never 'disappears'. You will also notice that the shank tends toward becoming parallel with the seabed. So the fluke starts off at a sharp seabed fluke angle and slowly flattens out to 16 degrees to the seabed. If you check a drawing of a Mantus - if the shank is horizontal the fluke is at 30 degrees. This low angle appears to occur at whatever scope ratio is being used

If you look at other anchors when they are 'well set' and evaluate the fluke angle, to the seabed, you will find it to be around 30 degrees, plus or minus 5 degrees.

As anchors dive more deeply the angle further decreases. Shallow angles fluke return low holding capacity.

The peculiarity, the uniqueness (the only anchor I know to show this characteristic), of the Mantus with its 16 degree fluke to seabed angle is common - virtually every underwater image shows the shank at 16 degrees.

Now - if you have a grossly oversize anchor it does not matter - the effective area compensates for the shallow angle. Basically you are lugging around a mobile mooring. Additionally Mantus does set quickly, even if not 'well' and a well set Delta or Bruce will hold well - so well and good - the Mantus is simply inefficient in modern terms.

I have to winder why Mantus have never conducted any independently verifiable holding capacity tests.

Jonathan

Interesting theorising!!

My experience of the Mantus is that for a given weight of most concave anchor it has a greater fluke area, and concave anchors nearly all have greater fluke area than comparable-weight plough anchors. Buried fluke area is surely the ultimate criterion of a well-set anchor, or so Alain Poiraud maintained.

I am aware that 30 degrees entry from horizontal is an article of faith with many and most anchor designs, except the more bizarre, adopt this shank/fluke configuration.
Perhaps, though, the 16 degree entry of the Mantus caters for a considerably greater resistance to insertion into the sea-bed, occasioned by its high fluke area to weight ratio.
My Mantus also sets in about a boat-length - compared with 3-4 for a Delta or CQR.
I never use a snubber to pull my anchor in, if under motor I idle back until the chain is tensioned, then increase revs to 2000 - 2500 until all reverse movement stops and the boat fishtails. Only then do I put on a snubber, 3 - 10 metres of octoplait 14mm.
The result is, if I swim over the set anchor, that it is totally underground in sand, not even the roll bar or shank showing - in hard mud/clay, only the fluke up to the shank is buried.
Occasionally the anchor does not set perfectly 1st time. Both drags (in about 200 deployments) I've had on the Mantus has been in seagrass, when it's torn up a length of stolon about 6' long.
So perhaps your insistence on 30 being better than 16 is rather like the UK Conservative party "banging on about Europe".

However I do wonder about the OP's proposed snubber design as an extraordinary complication of a very simple concept.
Hanging it over the front seems so much simpler and quite OK for continuous Force 7 winds at anchor.

 

[Flica]

Jonathan, I have seen a lot of anchors underwater and the performance from the Mantus in that video is superb. I am not sure why you cannot see this, but with both the photos and videos I produce I do encourage people to make up their own mind.

Note there was nothing special about this set, although conditions were not ideal with a scope of only 3:1 in 4.4m of water. I only filmed the one set.



Personally, I think the anchor "tests" paid for and organised by the manufacturer are of limited value. The anchor manufacturer controls alł the variables, analyses the results, and invariably wins the comparison. Surprise surprise.

Sounds like drug tests paid for by the drug company!!
You'd, surely, be disingenuous to expect anything else

 

[GHA]

I believe in simple fuss free anchoring. It really does not have to be too complicated.

:encouragement:

Which is why I can't agree with using a snubber to set most of the time. Away from "difficult" soft or rocky bottoms why treat the anchor with kid gloves?
Decent hook, decent size, in the usually (in my experience around the N/S Atlantic anyway) generally good holding give it good burst in reverse then when the chain has straightened out and the bow does a big dip full revs in reverse for a little while. If the anchor can't cope with that then it probably won't cope with the huge 3am squall and big wind shift on the leading edge, nice to know it can beforehand

 

[Flica]

:encouragement:

Which is why I can't agree with using a snubber to set most of the time. Away from "difficult" soft or rocky bottoms why treat the anchor with kid gloves?
Decent hook, decent size, in the usually (in my experience around the N/S Atlantic anyway) generally good holding give it good burst in reverse then when the chain has straightened out and the bow does a big dip full revs in reverse for a little while. If the anchor can't cope with that then it probably won't cope with the huge 3am squall and big wind shift on the leading edge, nice to know it can beforehand

Exactly.
Works very well in the Med as well. I go one more - after the bow dips the stern will wag!! Then it's really home.

 

[Neeves]

Flica

Take a Rocna and a Mantus of the same weight - they have the same sized fluke. The Mantus looks big - but that just because of the huge roll bar - the flukes are the same size.

And if the US Navy conducts tests and shows an 18 degree fluke angle, on a Danforth type fluke, offers half the hold of a 30 degree similarly sized anchor I have to favour the US Navy, not Mantus. Furthermore if a video, Panope, shows a Mantus dragging where a similarly weighted Spade and Excel (which do have smaller fluke areas0 have set - then is simply adds a bit of credibility to the concept.

I do not recall the size of your anchor but assuming its sized around the same weight as a Delta for your yacht - you will be as safe. Mantus set quickly and reliably and and a well set Delta will hold (its weakness being it is not easy to set well). But set well and it will hold - confirmed by 1,000s of happy owners - so your Mantus is fine. its just been over hyped and is an inefficient use of steel - a Rocna would have been better - but then, you get what you pay for.

Jonathan

 

[noelex]

Decent hook, decent size, in the usually (in my experience around the N/S Atlantic anyway) generally good holding give it good burst in reverse then when the chain has straightened out and the bow does a big dip full revs in reverse for a little while.

This is quite a valid technique that works well most of the time. It is especially useful if anchoring under sail. Be a little careful in heavy weed or very soft mud, where I think it is less successful.

If not using a snubber with an anchor that sets rapidly, be cautious until you develop a feel for the amount of reverse momentum. The force can be enough to rip out cleats etc, but this is not a issue with a bit of experience.

A lot of cruisers using this technique apply several hard jerks using the boat's momentum and this is a good method of applying a lot of force if you want to bury the anchor a long way.

Some cruisers combine the techniques with a more gradual initial set followed by a few hard jerks using the boats momentum. This too is fine.

There are lots of ways to set the anchor.

 

[Flica]

The Mantus is the same weight as the CQR it replaced, 25lbs. Small for loa but right for weight according to their table.
The point I'm endeavouring to make, is that it buries, if you use the right technique.
The CQR I had also worked, but needed greater craftiness and effort to set it.
When I was in the market for a replacement anchor, (when noelex started publishing his pics) only the aluminium Spade was lighter, the ROCNA considerably heavier (and x2 the price) but all were underpriced compared to a replacement CQR.
So on the basis that you get what you pay for, all would have to agree the CQR was the "best". Only slightly more than the Mantus was the Delta. I had to import direct from Texas, the European distribution not yet in place.
Interestingly anchor weight-tables for given boats seem now to be very similar and "shop" prices more aligned.
Market parallel evolution?
Perhaps, being a medic, Greg Kutner has taken a leaf out of drug company marketing?

 

[Neeves]

Perhaps, being a medic, Greg Kutner has taken a leaf out of drug company marketing?

Very succinct. I was rebuked for saying something slightly stronger

The Mantus will set, eventually. It has a setting angle of 16 degrees so as long as you have the engine capacity it will set and disappear - but it will travel further to do so, simple geometry.

Prices could become 'even' more equal. As I have said the costs of Rocna, Mantus, Kobra and Delta are very similar for the same weight, same steel, same labour etc etc. The differences in the prices to us are inefficiency or profit.

Jonathan

 

[Neeves]

Interestingly anchor weight-tables for given boats seem now to be very similar

Coincidentally I did a similar analysis for the same sized anchor, say around 20kg, then Lewmar (for Delta, Claw and CQR), CMP (or Smith) for Rocna; Manson for Supreme and Anchor Right for Excel all suggest the same sized yacht (for that same 20kg anchor). This is odd, after all the brouhaha over the higher holding capacity of Rocna, Supreme and Excel in comparison with Delta, CQR (and Bruce) rather than Claw. Spade stands out of having a bit more confidence in their product. Nothing wrong with this - safety factors have simply been increased (and then individuals commonly increase one or 2 sizes further). But this pales when compared to carrying a mobile mooring with an anchor twice the size recommended. I excluded Mantus and Vulcan because neither have been subject to any testing, whether by the anchor maker or anyone else (such as a Classification Society) - so they have not been Proof Tested either. I also excluded the Kobra, similar reasons (no Proof Testing) and, including Knox, it is not available for the market that was the focus of my investigation (America).

Jonathan