Catenary?

[noelex]

It may - no actually will - have greater ultimate holding power, but that does not mean you can access that holding power.

The flaw in all these arguments about increase or loss in holding power is they are expressed in terms of the holding power you are starting with NOT the potential ultimate holding power. A 50% loss in holding power for a good anchor like like a Spade will always leave you with more holding power than even the maximum holding power of a poor anchor like a CQR given equal conditions.

You can really only discuss the role of anchor size while keeping the design and construction material the same.

I think the point you are making is that good anchor design is important. I would wholeheartedly agree, select the the best anchor design you can.

 

[Neeves]

Anchor threads of late seem to be degenerating into nonsense. There are posts trying to assert that the well established, basic rules of anchoring do not apply.

For anyone inexperienced who is reading this thread in the hope of gaining some knowledge it is important to understand that using a snubber (as you should do with chain rode) does not remove the need to deploy adequate scope.

Basic rules of anchoring were developed using Admiralty pattern, CQRs, Delta and Bruce all of which were common place in the 20th Century (and those anchors were arguably 'king' until, say 2010). We are now into the 3rd decade of the 21st century and have a large variety of anchors to choose from Spade, Rocna, Excel, Knox - all of which have hold double that of the 20th century designs. The newer anchors not only offer better hold (for which classification societies allow use of smaller anchors) but offer more reliable and easier setting.

We have good anchor designs but rely on anachronistic rules for chain and use of chain mostly developed in the '50s, '60s and '70s.. Beggars belief.

Anyone reading an article on anchoring in Yachting Monthly or PBO from the 1970s and reading your posts would see no difference between what you say and was said then - yet our anchors are twice as good, chain strength and reliability has improved immesurably and our knowledge on use of snubbers is rapidly being accepted. Some of us understand the value of elasticity in a snubber and quickly realised that elasticity can replace catenary - its cheaper, its lighter and it offers its advantages well beyond the limits of catenary.

We have experienced members here who cross oceans, who have had, or have. careers in 'sailing' and who have quantified their conclusions on anchoring who all disagree with your comments. They reject 'bigger is better', they use a snubber or snubbers and find no need for excessive scope.

If you look at chain spread sheets - they have not changed from 50 years ago and neither has the use of chain - as indicated and underlined by your posts.

Jonathan

 

[noelex]

they use a snubber or snubbers and find no need for excessive scope.

I am not sure where I have recomended excessive scope. In fact, I have been critical of your posts stating that for anchoring overnight you always use a minimum of 5:1. As to adequate snubbers, yes, they are essential. At least we agree on that point. I have been a strong advocate for many years.

 

[Tranona]

Johnathan

Well said. The underlying theme of this thread is that catenary is a good thing and heavier chain increases catenary so must be even more good to the extent that one poster (in another thread on the same subject) said it will "improve anchoring performance - I have no doubt". Anchoring performance was defined as better setting and higher holding as a consequence of catenary reducing the pull angle in relation to horizontal. Despite being asked there was no explanation as to how this was measured nor any evidence to show that it was true. The secondary question which is pertinent to my dilemma is how much the performance will be improved by replacing my 6mm chain with 8mm. I am still waiting for some form of answer but all I have is that effectively "everyone knows" because this principle has been use for years.

Despite the excellent youtube from Steve demonstrating the properties of catenary in a clear way the question of improved setting and holding as a consequence of lower angle of pull has still not been addressed while the limitations of catenary in respect of damping and the point at which any benefits of catenary are lost have been confirmed. The only thing that remains constant is that catenary where it is still there effectively increases scope and therefore reducing swinging circles - useful in crowded anchorages.

Interesting the original post by Vyv was to demonstrate the limitations of catenary and quickly followed by a link to Pete Smith's more detailed explanation as to why it was considered valuable in the past but now no longer relevant because of the developments in anchor design and chain strength and reliability. Yet we have several pages of on and off posts trying to show that despite all this it really is better to have the heaviest chain and biggest anchor you can handle with no evidence as to how or why this improves anchoring performance over the sizes indicated by the data on setting, holding power and chain strength applied to the boat in question. Instead we are referred back to the essentially unchanged recommendations from the past which were based on a weight/boat length relationship. does make life easy for the work experience guy in the chandlers "36' boat? that will be a 15kg anchor and 8mm chain." next customer "38' boat? you will have to go up to a 20kg anchor and 10mm chain."

Sometimes I wonder why we need all this research and testing endorsed by plenty of personal experience to carry out an assessment for our specific needs and then make an informed choice when really all we need to do according to some is just get the biggest and heaviest you can handle.

 

[roaringgirl]

OK. Accepting all this & the NZ article, and being in the market for a new anchor and chain in due course, can the panel advise on the following.

1. Should I up size my anchor (currently a 25kg CQR on 60m of 10mm chain holding a 36' 10 tonne yacht)? I won't ask which anchor type to buy but let's assume Rocna.

2. If I use a part rope rode, how do you take the load off the bow roller (which is a mini bowsprit)? I always use a V bridle at present, with a long V to midship cleats in reserve for strong winds.

3. How do you lift a rope/chain rode? I find the rope drum angle and swap to chain a little fraught.

Currently I was inclined to current rode and a 25kg Rocna.

Swap to chain is easy:
1. Pull up rope on windlass until the chain gets almost to the drum.
2. Attach tail of rode (still on windlass) to a cleat
3. Put chain-hook #1 on the chain as far away from the windlass as possible. Tie chain-hook rode to clear.
4. Release rode from cleat and remove from windlass drum. Chain hook now holding rode.
5. Attach chain hook #2 close to chain hook #1 and wrap the tail around rope drum on windlass.
6. Pull on chain-hook #2 with windlass until free chain can be lifted onto gypsy.
7. With chain on gypsy, remove chain hooks and haul away!

 

[Neeves]

OK. Accepting all this & the NZ article, and being in the market for a new anchor and chain in due course, can the panel advise on the following.

1. Should I up size my anchor (currently a 25kg CQR on 60m of 10mm chain holding a 36' 10 tonne yacht)? I won't ask which anchor type to buy but let's assume Rocna.

2. If I use a part rope rode, how do you take the load off the bow roller (which is a mini bowsprit)? I always use a V bridle at present, with a long V to midship cleats in reserve for strong winds.

3. How do you lift a rope/chain rode? I find the rope drum angle and swap to chain a little fraught.

Currently I was inclined to current rode and a 25kg Rocna.

I might agree that 60m of 10mm chain might be a bit short, why you are using 10mm chain, not 8mm, is a bit of a mystery. Why not buy a Crosby 'C' link and simply extend your chain. Crosby's "C" links are highly recommended, check Vyv Cox website (google 'Vyv Cox').

If you are looking at your windlass with concern - maybe look at a new windlass, Maxwell would welcome your support, with a 8mm gypsy and the 8mm chain will be lighter than the 10mm you are hauling around, be strong enough for your yacht-, use less room in your bow locker - and save you buying a "c" link . and your sailing performance will improve.

You can also prove your are not anchored in the last Century.

You could then look at adding a decent snubber/bridle:

Adjustable Snubber Bridle and Chain Hook - Practical Sailor

https://www.sailmagazine.com/diy/how-to-dealing-with-snatch-loads-in-an-anchorage

The art of snubbing, in the nicest possible way - Mysailing

https://www.sailmagazine.com/cruising/anchor-snubber-tips

The next question, which might deserve a new thread is your thought process to replace a 25kg CQR with a 25kg Rocna. Explain your thought process, here, or in your new thread. Replacing a 25kg CQR with a 25kg Rocna seems bizarre, but not unusual. You might want to support Peter (Smith) - he must be well into retirement (age) by now.


With a new smaller and lighter chain and a decent bridle/snubber you will enjoy the benefits of a full, lightweight, chain rode and the elasticity of nylon. If you look at your anchor replacement, logically, your new anchor will be cheaper, better (than a CQR), more reliable.

As I've mentioned - the rode should be looked at as integrated and matching components - snubber, chain, shackle, anchor, windlass

Take care, good luck

Jonathan

 

[Neeves]

Tranona,

Look at your dilemma in a different vein.

Consider a worst case scenario - and then decide how likely that scenario might develop.

Assume you are caught in the Scilly Islands, a Storm is forecast, and you and a multitude of others need to develop a sensible and safe strategy. You could leave and make a passage to a safer location. Or you could hang in there, NormanS reiterates that where he cruises in the summer (he is on passage there now) there are no bolt holes.

With limited options you are left looking at a 5:1 scope and a decent anchor. You might have a rode for 10:1 but the popularity of the Scillies leaves that as a dream. I would not rely on the yachts at your stern all dragging leaving you room to deploy more chain.

Endless catenary is not the panacea - what to do?

To me its a no brainer - you need a decent snubber, as the snubber will replace any and all catenary and will do so, roughly linearly, upto the breaking strain of the snubber. If you are going to rely on a snubber you really do not need heavy chain, in your case 8mm, as a sensible snubber will provide all the energy absorbing ability you need. Instead of 8mm chain you could consider 6mm. If you have a 'modern' anchor (and I recall you have invested in a Lewmar Epsilon) - its hold, for a 15kg model is 2,000kg (its awarded SHHP and thus has a similar hold to Excel, Rocna, Spade). I don't know the Scilly Islands but assume your anchor's hold is diminished by 'poor holding' and the hold is actually 500kg. Consider that the hold of 2,000kg was measured at a 5:1 scope - which is the hold and scope measured when a 15 kg Excel was measured against a Supreme and Rocna. Scope does impact hold - but that is 'factored' into the measured hold.

With 500kg snatch loads (no snubber), measured on a catamaran with higher windage than your yacht, you will be concerned, not that the anchor will drag, but whether your bow roller was designed for such loads. Snatches of 500kg 'feel' catastrophic (I cannot emphasise the concern that a 500kg tension engenders).


I confess we sail where 'company' is the exception and with a Storm forecast we would deploy a second anchor in a 'fork' or 'V'. We do this, not because we doubt our primary rode, but because it simply seems cautious and its not a reality TV SAS exercise. I also firmly believe minimising yawing offers positive support to the anchor. (Its a bit like wearing a seatbelt, carry LJs or LR - we have never, ever needed these devices - but its easy to apply and if the unforeseen happens it might be useful). Forecast for most parts of the world give warning of Storms - what else are you doing?

The snubber you need must offer elasticity and for your yacht 8mm or 10mm nylon will be more than enough. I'd commend you have a snubber you can extend, deck length for everyday and 2 times deck length for my Scilly storm. Make sure you have a good chain hook and a back up snubber (snubbers do fail). If your snubber never fails - you either anchor in benign conditions, only, - or it is insufficiently elastic.

We use 12/13mm kernmantle climbing rope (38' 7t cat) - if you ask Marlow they can make similar or you can buy from most rock climbing retail outlets - or find someone whose rope has past its use by date. Kernmantle rock climbing rope has an abrasion resistant cover, so better than normal 3 ply nylon.

I don't 'know' your yacht but I would be trying to engineer a bridle, as a bridle (like a 'fork' or 'V' anchor) will reduce veering. I'd also suggest that if you have a strong point at the bow/waterline - a bowsprit pad eye - incorporate the device into your snubber - it will alter the scope -

If you want detail of that final statement - ask and I'll fill in the detail - but I'm already upsetting many who think I'm too verbose.

Jonathan

 

[Tranona]

I am not so concerned about those ultimate type scenarios partly because I don't sail in a way such that i will get in that situation and partly because I am confident that my anchor (which is 10kg, not 15) will hold if the holding is good enough and the chain will not break.

The claim for heavy chain rests on its supposed improved performance in setting and holding power. We have already established that once you get into conditions where high holding power becomes an issue the rode is essentially straight anyway. It is setting and getting the initial hold that is my concern because I anchor mostly in relatively benign conditions in generally good holding and depths usually in the 4-8m range. While I try to avoid crowded anchorages, they are often physically small so avoidance of dragging before setting is not good as there could be a shallow mud bank just behind, or a reef.

As I understand it from the various discussions in this thread the superior setting comes from the reduced angle of pull that catenary offers, equivalent to increasing effective scope while the boat is closer to the anchor (and further from the lurking mud bank). Much is made of the angle being 11 degrees and how it changes as the load increases until the rode is straight and at for example 5:1 is 20 degrees. I have seen nothing that tests the effect of these changes in angle on setting ability, nor what the optimum angle is for a specific anchor. The secondary related question is if a heavier chain is used which gives a different shape catenary and presumably a slower change in the angle when load is applied, does this improve setting? First there are no tests I can see that quantifies the role of the angle of pull nor how it changes with weight of chain.

Alongside this is a constant stream of tests and visual illustrations of how quickly NG anchors set at very low loads which leads me to think that there is no benefit in this part of the anchoring cycle to catenary in general and therefore no additional benefit in increasing catenary by deploying heavier chain. If you go through the recent threads on this topic where claims have been made about the benefits of catenary and heavy chain I have asked for some concrete evidence to support the claims.

Still waiting

BTW a couple of pictures of my boat. Heavy long keel, foredeck with big Sampson post, anchor out front on the side of the bow sprit and a new Kobra windlass. In its day considered THE small boat to go ocean voyaging. over 30 transatlantics in the late 70s when they were built. Totally wasted for pottering along the S coast but a vanity project for me and a way of using up surplus funds now we can no longer travel. The first photo when I bought it, the second the foredeck- not actually my boat but exactly the same anchor arrangements and last as it is now.

 

[noelex]

I anchor mostly in relatively benign conditions in generally good holding and depths usually in the 4-8m range.

If you are anchoring in good substrates, especially in relatively benign conditions and shallow depths, there is little benefit to chain weight. Modern anchors set so well in reasonable substrates that they perform well even with all rope rode.

The benefits of heavy chain are not high, especially considering the weight penalty involved. If you have the option putting the weight into the anchor this is far more efficient, but it is wrong to dismiss the benefits of weight in the chain completely. The benefits are mainly in helping the anchor set in difficult substrates.

Much is made of the angle being 11 degrees and how it changes as the load increases until the rode is straight and at for example 5:1 is 20 degrees. I have seen nothing that tests the effect of these changes in angle on setting ability, nor what the optimum angle is for a specific anchor. The secondary related question is if a heavier chain is used which gives a different shape catenary and presumably a slower change in the angle when load is applied, does this improve setting? First there are no tests I can see that quantifies the role of the angle of pull nor how it changes with weight of chain.

When the anchor is first dropped on the seabed the anchor has no grip. The rode will be lying on the seabed. As the initial load is placed on the anchor if an all rope rode is used the anchor will immediately experience a direction of pull above the seabed. The angle will be determined primarily by the scope deployed at this point. If you start setting with a 5:1 scope this angle will be close to 11.5° (not 20° as listed above). This assumes the seabed is flat where the anchor is dropped. In resonable substrates any decent anchor can start digging the toe into the substrate despite angle of pull, but this becomes harder in difficult substrates. If chain is used in this initial setting phase when the anchor has minimal grip, the chain will still be lying on the seabed and the direction of pull will be parallel to the seabed. The lower the angle of pull, the more easily the anchor can start to dig in.

As the anchor starts to set the force involved will increase and the chain will start to rise. We can use Panope’s data (see post# 92). He is measuring at a shorter 3.5 : 1 scope. At around 300lbs of force the chain will still be parallel to the seabed (according to his measurements with 105 feet of 3/8 chain). This is a moderate setting force. Panope reports in 20 knots of wind his boat is pulling 200lbs. With all rope rode the angle would be about 16.6° instead of 0°. Once again this pull parallel to the seabed makes little difference in reasonable seabeds, but helps the anchor start to set in difficult seabeds. As the force rises the advantages of the chain weight starts to diminish significantly at 1000lbs.

As the force rises, if the boat can generate 800lbs of pull the chain will be sitting at 10.5°, once again versus the 16.6° of all rope rode. According to Panope this is equivalent to around 40 knots of wind, although personally I think the force especially during snatch loads may be higher. A good anchor should not be troubled by 40 knots, once again expect in poor substrates.

In the above comparison we are looking at reasonably heavy chain (for the boat size) versus all rope rode. In practice few cruising sailors would choose all rope rode and the differences will be less if we compare thin chain with heavy chain.

So in summary: For best performance for the least weight keep the rode as light as practical and put the weight into the anchor, but do not totally dismiss chain weight as useless. It particularly creates an advantage in helping the anchor set in difficult substrates.

Nice boat BTW.

 

[Tranona]

Thank you for that.

I follow the thinking and the description of what happens - but that is not really my question which was does it make any material difference with modern anchors? What you describe is essentially qualitative as there is a lack of any rigorous testing that clearly shows an anchor sets quicker and better at lower angles of pull and many videos show the toe and shank of the anchor burying first then the angle of pull within such a narrow range seems irrelevant, As your explanation reads your qualification of when it might be useful get narrower and narrower to the extent that you almost dismiss its value. Really no different from the conclusion I came to and to Pete Smith's explanation. You may recall the West tests in 2006 also considered introducing (more) catenary into their test rode because they thought it might make a difference, but rejected it as not worthy of consideration. Maybe though they are influenced by the US preference for mixed chain/rope rodes such as they actually used.

I am still unconvinced about the value of excessive weight in the anchor either when the whole purpose of recent anchor development has been to produce better setting and holding anchors by design rather than weight. This has by and large been successful. No problem with heavier anchors also having greater size and therefore holding power, but don't see any strong evidence that this can actually be accessed by a smaller boat which simply cannot generate the loads required. Yet, as I pointed out earlier Lewmar who make anchors of all 3 types (bad heavy plough CQR, better plough Delta and SHHP NG Epsilon) use essentially the same weight based recommendation in relation to boat size for all three. In my experience with essentially the same boat the 16kg Delta outperformed the original 35lb plough (which is now a garden ornament) and the 10kg Delta performed in much the same way as the 16kg, although I admit it was never tested in the same way as the 16kg. Based on the test data of the Epsilon I have every confidence that it will outperform all 3. After all that is why Lewmar developed the product, but clearly not confident they can promote it this way to an audience condition to believe that weight is the key driver of anchoring performance.

 

[noelex]

I am still unconvinced about the value of excessive weight in the anchor either when the whole purpose of recent anchor development has been to produce better setting and holding anchors by design rather than weight.

Yes, you always need to compare like with like.

A larger anchor will have a higher ultimate holding ability than a smaller anchor of the same design and construction material.

You cannot say the same if the design is changed. A smaller anchor of one design may well have a better performance than a larger anchor of a different design.

No problem with heavier anchors also having greater size and therefore holding power, but don't see any strong evidence that this can actually be accessed by a smaller boat which simply cannot generate the loads required.

A boat dragging is generating the loads required. By definition the holding power required is greater than the anchor is capable of generating in that substrate, at that scope etc.

 

[boomerangben]

………….Much is made of the angle being 11 degrees and how it changes as the load increases until the rode is straight and at for example 5:1 is 20 degrees……..

Just a point from technica point of view, a scope of 5:1 if straight gives an angle of about 11 degrees not 20. I’m not sure if I’m missing your point here but if 11 degrees is an optimum, a 5:1 scope is what to go for and if chain, it will be less than that anyway.

 

[Tranona]

A boat dragging is generating the loads required. By definition the holding power required is greater than the anchor is capable of generating in that substrate, at that scope etc.

But this does not necessarily mean that a heavier anchor will then hold any better although one would like to think that one of the same design would.

 

[Tranona]

Just a point from technica point of view, a scope of 5:1 if straight gives an angle of about 11 degrees not 20. I’m not sure if I’m missing your point here but if 11 degrees is an optimum, a 5:1 scope is what to go for and if chain, it will be less than that anyway.

Yes you are right - bit of brain fade there. The suggestion that 11 degrees is optimum comes from a general view from testers that 5:1 is the optimum scope therefore the angle of pull if the load is applied to make the rode straight is 11. In reality it starts at zero (chain on seabed) and increases with load so increasing the holding power by burying the anchor deeper, This is what noelex was explaining. It is unclear (at least to me) whether the angle is critical or whether it is the load. Panope for example uses 3.5:1 which of course means steeper angle of pull for a given load. In his opinion is the optimum scope for the seabeds he uses.

The key question for me is whether catenary contributes to better setting and holding with the varying angle of pull compared with the same load applied at the maximum angle as with a rope rode. That is does the low angle pull at low loads which only comes with catenary ensure better setting. The secondary question is that if it does then can this be improved by using heavier chain as claimed by some.

Hence my question as to whether there are any tests that isolate these factors and measures them so that comparisons can be made

 

[noelex]

This is what noelex was explaining. It is unclear (at least to me) whether the angle is critical or whether it is the load. Panope for example uses 3.5:1 which of course means steeper angle of pull for a given load. In his opinion is the optimum scope for the seabeds he uses.

The anchor will always have its maximum holding power and set best when the direction of force on the anchor is parallel with the seabed. In simple terms, any angle above this is trying to pull the anchor out of the seabed. This is why holding power increases as the scope is increased until a practical limit of diminishing returns is reached at somewhere around 10 : 1 to 14 :1. This does not mean you should always use these very long scopes. They are often simply impractical and antisocial.

Panope has selected a scope of 3.5 : 1 for many of his tests. This scope is chosen not to provide the best holding power or setting performance, but as a reasonable compromise to keep the amount of rode manageable. He acknowledges that the performance would be better if the scope was increased (see the video in post #92). This is because the angle of pull would be lower.

 

[Neeves]

We went through this some time ago but unfortunately the thread was removed and the technical data is lost. (Not entirely true - I still have the pictures, I still have the plots.)

You can take random pictures of set anchors, excepting Epsilon, there is insufficient or no data, and make an analysis of the way the anchor has set. You can take key facets of the anchor, the angles in the shank, the location of the fluke to the shank, the relative distance of how the fluke is buried. From this you can calculate the angle of the fluke plate.

Such pictures are random and commonly you have no idea, at all, on how the anchor was set - and I assume people set their anchors in a regular manner - but that will vary with each individual.

I confess not to have looked at every anchor but have tended to focus on Mantus, Rocna, Spade, Excel and Fortress - partially as I have my own models of each - but of varying weights.

I find that it does not matter, as long as the scope is not 2:1 nor does it matter what the seabed is but virtually every set I see of most of these anchors is with the fluke at between 25 - 35 degrees to the seabed. The exception is Mantus which sets within a much more narrow range around 16 degrees. Why the angle varies between 25 and 35 degrees has nothing to do with seabed, see below, nor on the initial scope.

It has been known for decades that setting an anchor in sand the optimum fluke/seabed angle is 30 degrees - and this is the angle that anchor makers are aiming for in their design. The angle of the fluke/seabed is determined by a number of factors, crown location and ballast. All unballasted anchors have their crown at the heel, except Mantus, all ballasted anchors have their crown part way along the 'length' of the fluke.

You can do this determination yourself. Take random pictures of set anchors, take drawings of the set anchors, marry the pictures to the drawings - and you will derive the same conclusions I have done.

The best example of the impact of design is to look at a set Mantus, a Fortress (with flukes set at 32 decrees) and a Rocna or Spade, which are both ballasted. What you will find is that no matter what - the Mantus fluke is at 16 degrees and the Rocna and Fortress fluke at around 30 degrees. The difference is stunning and consistent. An Excel is a bit more difficult as its fluke is a complex shape - not a simple plate.

In setting the ballast chamber, other than carrying the ballast, has no impact, none whatsoever, on the setting characteristics - it is not an impediment to burying as when the anchor is setting it is moving forward and the ballast chamber simply 'fills' the hole or space, excavated by the flat of the fluke plate.

The size of the anchor does not matter, the results are the same - except that for a given tension the heavier anchor buries more shallow than the smaller anchor. The bigger anchor protrudes more above the seabed - the hold in a straight line will be the same, the tension is the hold, but a sideways tension will capsize the larger anchor (because of the lever arm effect), whereas the smaller anchor will rotate within the seabed - supported by the vertical 'fluke' effect of its buries shank.

The variation in many anchors, that data of 25-35 degree fluke to seabed angle. I do know that if an anchor encounters any foreign matter, shell, waterlogged wood, heavy kelp stalk that these items will have a negative impact on the development of hold. But unless you stop the set and dig up the seabed - you simply don't know. I set anchors in the intertidal zone - and can dig - but I'm an exception (most people anchor in deeper water. ).

Basically setting an anchor at 3:1 and then deploying more rode to 5:1 makes no difference to the final set of the anchor. Using 8mm chain or 6mm chain makes no difference to the eventual orientation of the anchor. Move the crown - and all bets are off - as illustrated by a comparison of a Mantus and Fortress, both unballasted anchors.


If anyone finds all this a difficult concept to accept I can extract some key pictures of set anchors, key plots of hold vs fluke angle - but I have completed this previously and I am sure many of you know exactly what I mean. I could offer the pictures and plots later today, my time, in about 12 hours time.

Noelex has a thread on CF of pictures of set anchors. Simply take his 'album' take out some key pictures (best pictures of anchors in sand, mud and clay (not weed (it obscures), take drawings of anchors from manufacturers websites - and make your own analysis.

Difficult seabeds - I don't know what the term means (and have never had it explained) - but I do understand weed - and in this analysis is not relevant as you can often see insufficient of any anchor to come to a conclusion). You can also argue that Mantus is ballasted, I think you are wrong - but it matters not a jot - Mantus consistency and uniquely sets at 16 degrees.

What is interesting is that Rocna, Spade, Fortress (and other anchors) all set focussed at that 30 degree fluke angle - no matter who or how the anchor was set. Similarly Mantus sets at that consistent 16 degrees whether I set the anchor, in various ways with a dyneema, 6mm or 8mm rode, or Noelex set the anchor. By set I mean once the anchor is stable and accepted as secure. Prior to being set I would use the word 'engages'

Tranona - basically your Epsilon will set in the same manner whether you use 10mm or 6mm chain, 3:1 or 5:1 scope - if you set at 3:1 scope the fluke angle may be 'less' but once you deploy 5:1 scope the anchor will 're-oreintate' to that 30 degree fluke angle. If the seabed is harder it may set more shallow - but the angle will be the same. Epsilon like an Excel has a complex fluke shape - determining the fluke angle is less easy (than a Fortress or Rocna).

However - most anchors set with the toe and the shackle engaging together, as one buries the other buries. If you use 10mm chain, instead of 6mm chain it will be an impediment to burial - but no-one in their right mind would replace 6mm with 10mm. Can you tell the difference between 8mm or 6mm, not in my view - but there will be an effect - but masked by natural variation in seabed.

Jonathan

edit

If you look at Noelex pictures of his Mantus - it does not matter what the seabed is, nor the scope at which he set (which maybe constant (or not) nor the scope he eventually used for his time at anchor - but the attitude of his mantis to the seabed is essentially identical - despite variations in depth, seabed, seabed consistency. That long of the shank - the part to which the shackle is attached is always parallel to the seabed and essentially horizontal. Mantus is not unique other anchors similarly have their own attitude which is again the same - despite different scopes and seabeds. The anchor effectively self rights to the same attitude, presumably the attitude the designer wanted - no matter what.

J

 

[GHA]

Not a regular here any more so there will be no replies to this post from here.
Breaking from forum tradition here by actually looking & measuring the real world ..
And having a play around with the data in grafana to see if there might be some patterns hiding away, whech there is! 5m average boat speed * 100 & 5m average wind speed correlate pretty well.

Heavy steel 10m long keel cruising boat. Little tidal flow in the anchorages.

Which also matches the physics very nicely, 20Kts exerts 64 X more force & same goes for the increase in kinetic energy when the boat accelerates.

Oscillations as the boat yawed through the wind seemed fairly regular against changes in aws but there might be something of interest in there somewhere.

If anyone fancies a chat pop over to this discord server > Join the Raspberry Pi boat monitoring Discord Server!

Some csv data will get uploaded for a play.

Masses of data is easy to save & peruse for patterns using signalk & influxdb. Runs Linux & windows, not sure about Mac.

 

[noelex]

Not a regular here any more so there will be no replies to this post from here.

That is a pity. I have appreciated your previous input on these threads.

The collection of this type of data can be useful in understanding how a boat behaves at anchor. Thanks for the graphs.

Perhaps I am not understanding correctly, but the SOG legend seems to missing from the first graph. It would be nice to know what boat speeds in addition to wind speeds were being recorded.

 

[doug748]

The anchor will always have its maximum holding power and set best when the direction of force on the anchor is parallel with the seabed. In simple terms, any angle above this is trying to pull the anchor out of the seabed. This is why holding power increases as the scope is increased until a practical limit of diminishing returns is reached at somewhere around 10 : 1 to 14 :1. This does not mean you should always use these very long scopes. They are often simply impractical and antisocial.

Panope has selected a scope of 3.5 : 1 for many of his tests. This scope is chosen not to provide the best holding power or setting performance, but as a reasonable compromise to keep the amount of rode manageable. He acknowledges that the performance would be better if the scope was increased (see the video in post #92). This is because the angle of pull would be lower.

Yes. A number of Panope's early videos did look at the effects of shortening scope and it clearly reduces holding power. However some of the break out angles were very high, demonstrating that short scope can be tenable should circumstances dictate. Most people will have tested their back in getting out a well set anchor is good holding, however when the holding is not so reliable most will want to weigh the odds in their favour.
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[noelex]

Yes. A number of Panope's early videos did look at the effects of shortening scope and it clearly reduces holding power. However some of the break out angles were very high, demonstrating that short scope can be tenable should circumstances dictate.

Absolutely. Utilising short scopes is a very valuable option to have available. It opens up many anchorages and anchor locations that would otherwise be untenable.

You do need to recognise that short scopes will diminish the maximum available holding power of your anchor. This is one reason why I am in favour of choosing the best anchor design and then fitting the largest size that can be comfortably managed. This combination provides the highest ultimate holding power so sacrificing some available holding power by using shorter scopes becomes more practical.

Shorter scopes than normal include both scopes that are traditionally regarded as short such as 3:1 (and less) and using more normal scopes such as 4:1 or 5:1 in very strong conditions where longer scopes are normally chosen.

The above is not to suggest that shorter scopes than normal should be routinely used, especially without careful thought. The quality of the substrate is often an unknown factor so having reserve potential holding power is valuable. The chain does not do any good in the chain locker. Nevertheless, if you have excellent ground tackle the option of utilising shorter scopes and can do this safely can be invaluable. The alternative of never being able to safely anchor overnight with less than 5:1 as reported by proponents of very minimal ground tackle can be made to work but is unnecessarily restrictive.