mainsail1
Well-known member
I was surprised at the way he dismissed any anchor with a hoop without proper explanation as to why.
So the £3000 plus, Ultra anchor was chosen!
- Thread starter Zagato
- Start date
noelex
Well-known member
I think it is simply that powerboats, especially small powerboats frequently have problems fitting anchors with roll bars.
I suspect Lewmar have gone to the expense and trouble of designing a roll bar because the anchor sets better with one installed, but they deem the performance still acceptable without the roll bar. By making the roll bar removable those boats that cannot fit a roll bar anchor are not excluded from the pool of potential buyers.
I have not seen the new anchor so the above is speculation. It will be interesting to see how the anchor performs with and without the roll bar.
Neeves
Well-known member
Generalising and profitably the question could be asked another way.
Why have a roll bar at all?
Bruce patented the idea, but never used it. Delta (ballasted, convex) was introduced, after the Bruce, (unballasted, concave) and neither has a roll bar. Spade, ballasted and concave, has no roll bar. Kobra, (convex. ballasted) has no roll bar. Ultra, (concave, ballasted) has no roll bar. Excel, (ballasted concave/convex) has no roll bar, Vulcan, (ballasted, concave) has no roll bar and now Epsilon (convex/concave ballasted).
To me, and I note others think it of less importance, are primarily about holding capacity .... then plus other characteristics. What does a roll bar add to hold that could not be produced more effectively with a slightly bigger fluke?
What is the advantage of a roll bar - handle if you need to carry down the deck (think of racing yachts), it self rights the anchor (see above - they all self right)
For most unballasted fluke anchors, Danforth, Fortress (they use a hinge - there is no 'upside down'), Bugel, Mantus, Knox, SARCA, Viking - they need a roll bar - could they be re-designed without a roll bar?? - probably not..... or....maybe?
There is an undercurrent, a subjective belief, that along with buying an anchor bigger than recommended ( search YBW for and see 'Dragging of anchors' and 'Dragging of Anchors 2') that a modern anchor needs a roll bar and maybe needs to be concave (see clogging of flukes etc etc). Maybe Lewmar rightly thought I - 'if that's what the market believes give it to them - its easier than trying to educate them'
Many vessels cannot accept a roll bar anchor, ours for one, many other multihulls, yachts with bow sprits etc etc. So if you want to address all the market you need an anchor with a removable roll bar and as Ultra prove - you need both stainless and galvanised (as for some there is no shortage of money). The alternative is designing different anchors, Rocna, Vulcan? Excel, SARCA?
So milk the various segments of the market as much as you can. Pander to every whim and fancy - but make sure you maximise sales and profit.
Jonathan
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Zagato
Well-known member
It is worth mentioning that stainless steel will corrode eventually. There are risks during production from contamination of metals, the actual welds, the heat of the welds causing possible scaling and the joining together of two different metals, I call this electrolysis in my work ( i wonder if the two types stainless steel I.e. 316L and Duplex on the Ultra for instance would come into this category!). It is a gamble of longevity against cost!
5 Things That Will Corrode Stainless Steel
5 Things That Will Corrode Stainless Steel
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Neeves
Well-known member
Damning, or trolling, an anchor on the basis of one set seems questionable.
We do not know how the anchor was set, we don't know the seabed, we don't know the expertise of the individual setting the anchor and we do not know if the anchor has caught something, foreign, in the toe.
The ability of an anchor to set is normally based on 3 sets in 3 different seabeds with anchors of 2 different sizes in comparison with a standard anchor (in this case it would be a Supreme or Spade of the same weight), under controlled conditions.
Jonathan
Seven Spades
Well-known member
I had a Rocna, now I have a spade. I hated the roll bar for what could get stuck in it or it could hook on to. However now I worry that the Spade is not as good as the Rocna... The truth is I haven't had a problem with the Spade, but when you have had a Rocna it is difficult to have that much confidence in other anchors.
I am however convinced that the Ultra is better than the Rocna but the sheer cost is holding me back.
I am however convinced that the Ultra is better than the Rocna but the sheer cost is holding me back.
Zagato
Well-known member
My novice take on this from hours Googling is that the Spade sets equally well as the Rocna but on re set the Rocna could fail due to the roll bar. The Spade does not have this problem so the Rocna is out for me as I nearly always experience a tide change of direction in mud and weed!
I like also the fact that the Spade can be broken down... I wonder if anyone has devised a way of fixing the shank securely with a quick release bolt of some sort. I am just looking at the Kobra as well that breaks down for interest.
One disadvantage with the lead tipped weighted anchors is that it seems for me anyway that the recommended weight of anchor is more than the previous gen of anchors. For my little 26' 2250KG boat Rocna themselves emailed me to say I need a 10KG anchor with a minimum of 7mm chain (even though it says 6mm on their chart) The Spade comes out even heavier at 10KG plus but the Kobra is 6-8KG on their chart as is the Delta!
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Neeves
Well-known member
If you take a Rocna anchor and lay it on top of the Spade and look down on them - the two flukes are identical. The difference is the ballast on the Rocna (is steel) and spread over a larger area. The Spade ballast is focussed in the toe (and is lead). The 2 shanks are identical, or almost so (and a copy of the Delta shank). If you take the Delta shank and a set of French curves and curve the corners of the Delta with the curves - you get a Spade shank. If you put the Spade and Rocna side by side the top surface of the Rocna is a 'cheap' way of making the shallow bowl shape of the Spade. Basically it seems as if the Rocna is another way of arriving at what Spade has achieved. However because the ballast is less focussed - Rocna needs a roll bar. When I was searching for an anchor to replace a copy CQR Craig advised that Rocna only needs a roll bar for 1 in 10 times and the introduction of the Vulcan seems, to me, to suggest that Peter Smith admired Spade and wanted to make one - but improve on it. I've not come up close a personal with a Vulcan - so will comment no fiurther. You cannot judge an anchor by looking at it - you, not someone else, you need to use it.
The fact that Rocna and Spade perform so similarly - is not a surprise, to me. I prefer the absence of the roll bar (for the reason Zagato suggests + the focussed ballast allows it to address weed more effectively) and I like the demountability. I'm also keen on the aluminium version. In terms of hold - I'd challenge anyone to differentiate blind fold. We also cannot use a Rocna - the roll bar fouls the yacht.
I cannot comment on weight recommendations except that we have the windage of a 45' yacht and safely use 15kg, Spade or Excel - in the aluminium versions 8kg each (but do deploy a second anchor when twitchy). The whole basis of using a SHHP anchor should be, compared to a HHP (Delta) that you can use a lighter anchor. Check what weight Spade or Rocna say for a 45' mono or a 38' cat. BUT - I do not recommend the size of anchor for anyone, that's for you and the anchor maker. And we use 6mm chain (75m) and our second rode is 15m of 6mm chain with the rest, 40m, nylon 12mm x 3 ply.
And no - we use the nylon nut and bolt supplied by Spade with the cotter pin. For our Kobra - I had ours welded up. But we don't carry it (its steel and Spade and Excel are better).
I could not buy an Ultra - my Scots presbyterian upbringings will not allow it. Its an anchor - its really good, its beautiful - but its just an anchor and it is not better, blindfold, to an Excel or Spade. Most of us want our yachts to be admired for what they are, not for the beauty of the anchor! . But if you think the Ultra enhances your yacht - go for it (I'd rather invest in a decent supply of malt).
Spade, Ultra, Excel, Kobra, Rocna (Supreme, Knox, Viking) - all excellent anchors - you will not notice the difference (unless you go grossly undersized).
Jonathan
The fact that Rocna and Spade perform so similarly - is not a surprise, to me. I prefer the absence of the roll bar (for the reason Zagato suggests + the focussed ballast allows it to address weed more effectively) and I like the demountability. I'm also keen on the aluminium version. In terms of hold - I'd challenge anyone to differentiate blind fold. We also cannot use a Rocna - the roll bar fouls the yacht.
I cannot comment on weight recommendations except that we have the windage of a 45' yacht and safely use 15kg, Spade or Excel - in the aluminium versions 8kg each (but do deploy a second anchor when twitchy). The whole basis of using a SHHP anchor should be, compared to a HHP (Delta) that you can use a lighter anchor. Check what weight Spade or Rocna say for a 45' mono or a 38' cat. BUT - I do not recommend the size of anchor for anyone, that's for you and the anchor maker. And we use 6mm chain (75m) and our second rode is 15m of 6mm chain with the rest, 40m, nylon 12mm x 3 ply.
And no - we use the nylon nut and bolt supplied by Spade with the cotter pin. For our Kobra - I had ours welded up. But we don't carry it (its steel and Spade and Excel are better).
I could not buy an Ultra - my Scots presbyterian upbringings will not allow it. Its an anchor - its really good, its beautiful - but its just an anchor and it is not better, blindfold, to an Excel or Spade. Most of us want our yachts to be admired for what they are, not for the beauty of the anchor!
. But if you think the Ultra enhances your yacht - go for it (I'd rather invest in a decent supply of malt).Spade, Ultra, Excel, Kobra, Rocna (Supreme, Knox, Viking) - all excellent anchors - you will not notice the difference (unless you go grossly undersized).
Jonathan
noelex
Well-known member
A good rule of thumb seems to be that as an anchor model decreases in performance, the manufacturer is more likely to recommend a smaller size
. I think a large factor is that by recommending small sizes the anchor model is more likely to be chosen by high volume boatbuilders (such as Beneteau etc) to be sold as standard equipment. It enables the boatbuilder to choose as small an anchor as possible without violating the anchor manufacturer’s recommendations. This has savings for the boatbuilder not just for the anchor itself, but more importantly for the anchor winch, bow roller and other associated equipment. These have to be sized to cope with the anchor weight. Lewmar recommends very small sizes for their Delta model and I think it no coincidence that this is the most popular anchor included with new boat purchases. To compete in this market other manufacturers are forced to follow suit.
In my view, the Rocna and steel Spade have very similar ability and so you can expect that the same size will be equally suitable. The Kobra and certainly the Delta do not perform as well. To try and reduce the performance gap, considering a larger rather than a smaller size of these models is more sensible.
Neeves
Well-known member
This is not correct, or not in Lemar's or Vetus' case.
Yacht manufacturers try to buy as much product from one supplier as possible - this means they can place on order with the component supplier and arrange one delivery. They can demand of the component supplier that pallets are made up for individual yachts, so they can have a series of pallets for a 35' another series of pallets for a 40' etc. This is especially valuable where the manufacturer of the yacht is building in countries other than their main location, say building in Poland or China etc
Few manufacturers can supply everything but Vetus, Plastimo and Lewmar do a pretty good job.
The choice of Delta is thus because the yacht manufacturer is focussing on Lewmar for their hatche, windlass and anchor etc. The Vetus range is not quite so extensive and they tend to play second fiddle. By buying in bulk the yacht manufacturer can also demand keen prices - which the boat buyer, hopefully, enjoys. The boat builder thus sources all the bits and pieces more cheaply than we can and probably more cheaply that a custom boat builder can negotiate.
The end result is that that many yachts are commissioned with a Delta anchor, though I have seen them, some French yachts, with Plastimo's Kobra . I have also seen French production yachts commissioned with Spade (there is a lot of loyalty to country).
If the boat builder wants to have a bigger anchor than Lewmar recommend, Lewmar will comply, and if the new owner of the yacht wants a bigger or different anchor, the boat builder will comply - but the new owner pays extra, extra as its a special (so guess what usually happens)
The anchor size supplied by Lewmar will meet Classification Society requirements as many yachts go to charter.
The size of the anchor will have no impact on the size of the windlass - the weight is in the chain not in the anchor - so the suggestion that choosing a smaller anchor allows a smaller windlass is, basically, absolute rubbish. The idea that upsize from a 10kg anchor to a 15kg anchor will demand a bigger windlass is a good joke - and brought a smile to my face (in these times anything that can make you smile is good!
). Oddly, and I confess this is subjective, but the feeling I have of new yachts is that they are supplied with chain larger than necessary (anyone who has made an accurate assessment - it would be useful to have feedback). My larger chain assessment maybe one of these choices made by the customer.As I have mentioned previously
If you average the spread sheets for Bruce, CQR and Delta and plot them against vessel size you will find good overlap, there are some discrepancies because the anchor sizes sometimes do not over lap. If you now do the same for Supreme, Excel and Spade and plot their averages and compare the 2 plots - they are almost identical. So though the new models have twice the hold of the old models the manufacturers choose not to recommending down sizing - they choose to double the safety margin. As someone pointed out it does not show much confidence by the newer models in performance.
This latter contradicts Classification Society recommendations where a SHHP anchor can be 30% smaller than a HHP anchor, so instead of the 15kg Delta you could use a 10kg Supreme.
Bucking the trend, and I have not made an accurate comparison of their complete range, but Viking seem to be recommending smaller (sorry let me be accurate, lighter) anchors (vs the size of yacht) and the owner of Viking, I believe, is using a Viking 10 on a newish 43' Jenny. Their Viking 10 is about the same size as many other 15kg anchors - because they use HT steel in the fluke (saving weight - and its surface area not weight + design that produces the hold). Their quoted holding capacity data reinforces what they recommend and my test of a Viking 10 largely re-confirms their data. However it is not only surface area but fluke thickness - a thinner plate, again the use of that HT steel, of the same design will produce more hold. If you don't believe this - go find a thick plate of steel and a thin plate - tell me which is easier to force into wet sand.....
You can as Noelex suggests opt for a bigger anchor - but as the 2 threads seem to underline, 'Dragging of Anchors' and 'Dragging of Anchors 2' (you need to use the YBW search engine to find them) most people seem to think this unnecessary as having bought the recommended sized new gen anchor - they have not dragged. Interestingly it is not that they have dragged less frequently - they have not dragged at all. So buying a bigger New Gen anchor is, well - a waste of money (and if I'm wrong and Noelex right - you need a bigger windlass!
). But if you have plenty of money - why worry (except there are downsides with the bigger anchor - it will not set so deeply, might leave some of the anchor protruding and in a change of tide the chain might trip the anchor.......Jonathan
Izi Kalvo
Member
This is not correct, or not in Lemar's or Vetus' case.
Yacht manufacturers try to buy as much product from one supplier as possible - this means they can place on order with the component supplier and arrange one delivery. They can demand of the component supplier that pallets are made up for individual yachts, so they can have a series of pallets for a 35' another series of pallets for a 40' etc. This is especially valuable where the manufacturer of the yacht is building in countries other than their main location, say building in Poland or China etc
Few manufacturers can supply everything but Vetus, Plastimo and Lewmar do a pretty good job.
The choice of Delta is thus because the yacht manufacturer is focussing on Lewmar for their hatche, windlass and anchor etc. The Vetus range is not quite so extensive and they tend to play second fiddle. By buying in bulk the yacht manufacturer can also demand keen prices - which the boat buyer, hopefully, enjoys. The boat builder thus sources all the bits and pieces more cheaply than we can and probably more cheaply that a custom boat builder can negotiate.
The end result is that that many yachts are commissioned with a Delta anchor, though I have seen them, some French yachts, with Plastimo's Kobra . I have also seen French production yachts commissioned with Spade (there is a lot of loyalty to country).
If the boat builder wants to have a bigger anchor than Lewmar recommend, Lewmar will comply, and if the new owner of the yacht wants a bigger or different anchor, the boat builder will comply - but the new owner pays extra, extra as its a special (so guess what usually happens)
The anchor size supplied by Lewmar will meet Classification Society requirements as many yachts go to charter.
The size of the anchor will have no impact on the size of the windlass - the weight is in the chain not in the anchor - so the suggestion that choosing a smaller anchor allows a smaller windlass is, basically, absolute rubbish. The idea that upsize from a 10kg anchor to a 15kg anchor will demand a bigger windlass is a good joke - and brought a smile to my face (in these times anything that can make you smile is good!
As I have mentioned previously
If you average the spread sheets for Bruce, CQR and Delta and plot them against vessel size you will find good overlap, there are some discrepancies because the anchor sizes sometimes do not over lap. If you now do the same for Supreme, Excel and Spade and plot their averages and compare the 2 plots - they are almost identical. So though the new models have twice the hold of the old models the manufacturers choose not to recommending down sizing - they choose to double the safety margin. As someone pointed out it does not show much confidence by the newer models in performance.
This latter contradicts Classification Society recommendations where a SHHP anchor can be 30% smaller than a HHP anchor, so instead of the 15kg Delta you could use a 10kg Supreme.
Bucking the trend, and I have not made an accurate comparison of their complete range, but Viking seem to be recommending smaller (sorry let me be accurate, lighter) anchors (vs the size of yacht) and the owner of Viking, I believe, is using a Viking 10 on a newish 43' Jenny. Their Viking 10 is about the same size as many other 15kg anchors - because they use HT steel in the fluke (saving weight - and its surface area not weight + design that produces the hold). Their quoted holding capacity data reinforces what they recommend and my test of a Viking 10 largely re-confirms their data. However it is not only surface area but fluke thickness - a thinner plate, again the use of that HT steel, of the same design will produce more hold. If you don't believe this - go find a thick plate of steel and a thin plate - tell me which is easier to force into wet sand.....
You can as Noelex suggests opt for a bigger anchor - but as the 2 threads seem to underline, 'Dragging of Anchors' and 'Dragging of Anchors 2' (you need to use the YBW search engine to find them) most people seem to think this unnecessary as having bought the recommended sized new gen anchor - they have not dragged. Interestingly it is not that they have dragged less frequently - they have not dragged at all. So buying a bigger New Gen anchor is, well - a waste of money (and if I'm wrong and Noelex right - you need a bigger windlass!
Jonathan
So, first a disclaimer, I am the owner and CEO of Viking anchors.
My wife and I sail on a Jeanneau 43DS with a net weight of 10 tons, we are using a Viking 10 anchor that weighs 9.5 kilos and has a 743 Cm2 fluke area, 10mm chain, and we usually use a 5-meter long snubber.
Without getting too deep into our design and manufacturing philosophy, in our long voyage of research and testings our and others anchors, we have found out that there are 3 major factors that reflect on the holding power of a well designed, or newly designed anchor,
The surface of the fluke,
The angle of the fluke to the seabed after setting,
The depth of the anchor after setting.
We managed to achieve all three of them and more by using our unique design and the use of HT steel that allows us to make the Viking fluke thinner which absolutely affects the anchor's penetration and depth of setting.
Admin, I hope the above is fine with you, since Viking was mentioned my clarifications were needed.
beermonkey
Active member
Very true, always very well put together. What else would you expect from a former professional cameraman and mainstream tv journalist?
Neeves
Well-known member
Izi,
I guess the chain came with the yacht - but it will be remarkably heavy (and might explain your short snubber). The chain itself will be a deterrent to the anchor setting as deeply as you intended in your design (because the chain has a high surface area (or volume). You might like to consider adding a short length of smaller chain, and of higher tensile strength than the 10mm chain, short enough not to have need to pass through the gupsy. This way you will keep the catenary of the 10mm chain but allow the anchor to bury even more deeply.
Its a bit of a faff to arrange - but will better illustrate the advantages you claim for your anchor - if you take any underwater photos.
In case you do this - you need to take some photos now, with the 10mm chain to show us later if you use smaller chain. The photos ideally want to be in the same place, same seabed, and the anchor set with the same reverse power and same scope - or the comparison will lack some credibility.
Jonathan
a bit of background
Modern anchors commonly set with the toe and shackle burying together. The fluke continues to dive and pulls the shank end, with shackle and chain, into the seabed. Anchor makers try to reduce shank width to allow the anchor to bury more easily (which is why Peter Smith went to Bis 80 as it allowed a thinner shank). But the chain, shackle and swivel (if the latter is attached) also resists burial and retards the performance of the anchor. The chain develops a reverse catenary and as the shackle is buried the shackle angle increase, it slowly points more and more 'up'. Consequently the tension on the anchor is determined by the shackle angle - not the scope. (If you check Vryhof or Bruce website you will note they always denote a buried rode as a reverse catenary). Eventually the shackle angle gets so high that the anchor will drag through the seabed and it will have reached is maximum dive depth. The shackle angle is independent of scope - it varies with its size, the size of the buried chain and the shear strength of the seabed. Oil rigs use HT chain for the same reasons we do, they are lighter and they bury more easily.
Using a smaller shackle, but still strong and a smaller chain will enhance anchor performance. I have an article pending in which I dug anchors out to illustrate all of this - its real! The US Navy and the oil industry have computer programmes so that they can calculate anchor depth and shackle angle etc.
It merits note that we focus on scope but the tension angle of a modern anchor is independent of scope. In fact the tension angle can be quite high (much higher than the angle determined by scope) - yet modern anchors continue to perform. Modern anchors can perform at quite high tension angles, they will continue to dive. Scope is important initially - so don't ignore it - but we should be focussing more at making our rodes a bit more skinny if we want to maximimsie the performance of our anchors. No swivel, smaller higher tensile chain, smaller shackle (Grade B like the Crosby G209 a quality)
J
I guess the chain came with the yacht - but it will be remarkably heavy (and might explain your short snubber). The chain itself will be a deterrent to the anchor setting as deeply as you intended in your design (because the chain has a high surface area (or volume). You might like to consider adding a short length of smaller chain, and of higher tensile strength than the 10mm chain, short enough not to have need to pass through the gupsy. This way you will keep the catenary of the 10mm chain but allow the anchor to bury even more deeply.
Its a bit of a faff to arrange - but will better illustrate the advantages you claim for your anchor - if you take any underwater photos.
In case you do this - you need to take some photos now, with the 10mm chain to show us later if you use smaller chain. The photos ideally want to be in the same place, same seabed, and the anchor set with the same reverse power and same scope - or the comparison will lack some credibility.
Jonathan
a bit of background
Modern anchors commonly set with the toe and shackle burying together. The fluke continues to dive and pulls the shank end, with shackle and chain, into the seabed. Anchor makers try to reduce shank width to allow the anchor to bury more easily (which is why Peter Smith went to Bis 80 as it allowed a thinner shank). But the chain, shackle and swivel (if the latter is attached) also resists burial and retards the performance of the anchor. The chain develops a reverse catenary and as the shackle is buried the shackle angle increase, it slowly points more and more 'up'. Consequently the tension on the anchor is determined by the shackle angle - not the scope. (If you check Vryhof or Bruce website you will note they always denote a buried rode as a reverse catenary). Eventually the shackle angle gets so high that the anchor will drag through the seabed and it will have reached is maximum dive depth. The shackle angle is independent of scope - it varies with its size, the size of the buried chain and the shear strength of the seabed. Oil rigs use HT chain for the same reasons we do, they are lighter and they bury more easily.
Using a smaller shackle, but still strong and a smaller chain will enhance anchor performance. I have an article pending in which I dug anchors out to illustrate all of this - its real! The US Navy and the oil industry have computer programmes so that they can calculate anchor depth and shackle angle etc.
It merits note that we focus on scope but the tension angle of a modern anchor is independent of scope. In fact the tension angle can be quite high (much higher than the angle determined by scope) - yet modern anchors continue to perform. Modern anchors can perform at quite high tension angles, they will continue to dive. Scope is important initially - so don't ignore it - but we should be focussing more at making our rodes a bit more skinny if we want to maximimsie the performance of our anchors. No swivel, smaller higher tensile chain, smaller shackle (Grade B like the Crosby G209 a quality)
J
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Rappey
Well-known member
Fascinating thread !
Whilst we can look up figures for anchor holding power and chain strength how can I know what pull my boat can exert ?
What pull in 4knts of current, 12 knts of wind, large wash etc on a given vessel ?
Whilst we can look up figures for anchor holding power and chain strength how can I know what pull my boat can exert ?
What pull in 4knts of current, 12 knts of wind, large wash etc on a given vessel ?
Neeves
Well-known member
There are a number of articles on rode tension or rode loads, a google search will find them.
I did it for our cat:
Anchor Testing and Rode Loads - Practical Sailor
You and most others are simply too far away but if enough people local to me asked the question I'd quite happily bring my load cell and measure the tensions with you. Its not difficult, you just need a little patience to set it up - and some wind (and tide) preferably not both together. My recorder also needs A/C which I could rig up from our cat to the yacht 'almost' alongside. I'm sure you can hire a load cell - but I have no idea how much they might cost. Really the only way to derive the figures with any accuracy is to do it with your yacht. The spreadsheets will give indicative data but every yacht is different (they have different windage, furling headsails, biminis, dinghies etc. If you store the dinghy on the foredeck when you make a passage, and leave it there when you anchor, your windage and propensity to veer will be different to the identical yacht with a dinghy on davits and different to one with the dinghy on a painter.
The tension in your rode is the same tension as applied to the anchor. So if you experience a snatch load on your yacht - your anchor enjoys the same impact.
The maximum tensions developed are from a veer (and probably adding some chop and swell). So minimising veering and managing chop and swell will reduce the size of snatch loads. Using a snubber dampens any snatch loads (better than chain because when snatch loads become an issue when your catenary support has basically disappeared)..
How to: Dealing with Snatch Loads in an Anchorage
Anchor Snubber Tips
This third article gives our experience in reducing the impact of chop - but you need to read right through to find it, our vertical 'bridle', and then use a bit of lateral thinking on how to apply to a monohull. It has been applied to a yacht - it is possible.
Running the Lines on the Multihull Bridle - Practical Sailor
A rule of thumb for your engine - about 100kg of tension in the rode for every 10hp. Starzinger and I both tasted this, completely indpendently, and achieved the similar data.
BUT
I described this in an earlier post
As you reverse up you lift the chain and stretch your snubber and the increase in tension slows the yacht, the yacht continues in reverse because it has momentum and you slowly flatten out the catenary and stretch the snubber. Your engine has a fixed ability to continue to move the yacht backwards but some of the reverse movement is due to the engine and some is momentum - but the potential energy in the catenary and snubber eventually becomes,es more than the kinetic energy of the yacht (because the speed decreases) - eventually the yacht stops. Now there is no momentum (energy only of the engine) but the kinetic energy in snubber and catenary was developed by both momentum and the engine and is now larger than the engine - so the yacht moves forward.
As the engine is still running the engine becomes garter than the momentum moving forward and the yacht moves back - this will continue as long as you like.
Each maximum is transitory.
If you used a dyneema rode - this would not happen as you have no elasticity and no catenary (of little of either)
This is why I would not use a snubber when power setting (except a short one to take the load off the windlass).
The 10hp/100kg is on the basis of an all chain rode, no snubber. You may not notice this yo-yo effect, because you have no fixed point, but you can see the catenary straightening and slackening. The longer you can make a 'run' at power setting the more momentum you can develop - I'm a bit twitchy of doing this as it is very difficult to control.
At full revs in reverse most yachts (with an auxiliary motor) will develop the tension imposed by a 30 knot gust, plus or minus, might be 25 knots to 35 knots. A veer is an added complication as the tension is not in the same direction as average and a bit of chop introduces a vertical element of tension that was not available when you power set (but note my comment on shackle angle and how modern anchors seem better able at performing even though the tension is 'high' ish.
The deeper you set you anchor the more chain is buried the more stable your anchor (at least up to a point). Buried chain will resist veering, because it has to 'veer' through the seabed.
Jonathan
I did it for our cat:
Anchor Testing and Rode Loads - Practical Sailor
You and most others are simply too far away but if enough people local to me asked the question I'd quite happily bring my load cell and measure the tensions with you. Its not difficult, you just need a little patience to set it up - and some wind (and tide) preferably not both together. My recorder also needs A/C which I could rig up from our cat to the yacht 'almost' alongside. I'm sure you can hire a load cell - but I have no idea how much they might cost. Really the only way to derive the figures with any accuracy is to do it with your yacht. The spreadsheets will give indicative data but every yacht is different (they have different windage, furling headsails, biminis, dinghies etc. If you store the dinghy on the foredeck when you make a passage, and leave it there when you anchor, your windage and propensity to veer will be different to the identical yacht with a dinghy on davits and different to one with the dinghy on a painter.
The tension in your rode is the same tension as applied to the anchor. So if you experience a snatch load on your yacht - your anchor enjoys the same impact.
The maximum tensions developed are from a veer (and probably adding some chop and swell). So minimising veering and managing chop and swell will reduce the size of snatch loads. Using a snubber dampens any snatch loads (better than chain because when snatch loads become an issue when your catenary support has basically disappeared)..
How to: Dealing with Snatch Loads in an Anchorage
Anchor Snubber Tips
This third article gives our experience in reducing the impact of chop - but you need to read right through to find it, our vertical 'bridle', and then use a bit of lateral thinking on how to apply to a monohull. It has been applied to a yacht - it is possible.
Running the Lines on the Multihull Bridle - Practical Sailor
A rule of thumb for your engine - about 100kg of tension in the rode for every 10hp. Starzinger and I both tasted this, completely indpendently, and achieved the similar data.
BUT
I described this in an earlier post
As you reverse up you lift the chain and stretch your snubber and the increase in tension slows the yacht, the yacht continues in reverse because it has momentum and you slowly flatten out the catenary and stretch the snubber. Your engine has a fixed ability to continue to move the yacht backwards but some of the reverse movement is due to the engine and some is momentum - but the potential energy in the catenary and snubber eventually becomes,es more than the kinetic energy of the yacht (because the speed decreases) - eventually the yacht stops. Now there is no momentum (energy only of the engine) but the kinetic energy in snubber and catenary was developed by both momentum and the engine and is now larger than the engine - so the yacht moves forward.
As the engine is still running the engine becomes garter than the momentum moving forward and the yacht moves back - this will continue as long as you like.
Each maximum is transitory.
If you used a dyneema rode - this would not happen as you have no elasticity and no catenary (of little of either)
This is why I would not use a snubber when power setting (except a short one to take the load off the windlass).
The 10hp/100kg is on the basis of an all chain rode, no snubber. You may not notice this yo-yo effect, because you have no fixed point, but you can see the catenary straightening and slackening. The longer you can make a 'run' at power setting the more momentum you can develop - I'm a bit twitchy of doing this as it is very difficult to control.
At full revs in reverse most yachts (with an auxiliary motor) will develop the tension imposed by a 30 knot gust, plus or minus, might be 25 knots to 35 knots. A veer is an added complication as the tension is not in the same direction as average and a bit of chop introduces a vertical element of tension that was not available when you power set (but note my comment on shackle angle and how modern anchors seem better able at performing even though the tension is 'high' ish.
The deeper you set you anchor the more chain is buried the more stable your anchor (at least up to a point). Buried chain will resist veering, because it has to 'veer' through the seabed.
Jonathan
Rappey
Well-known member
Great to see some loads for given wind strengths.
Would be very interesting to see a similar test with no wind but 1m waves or more.
Would be very interesting to see a similar test with no wind but 1m waves or more.
Neeves
Well-known member
I actually chose my location so as to have wind but no waves. If you have ever seen Home and Away my location was on the inside and below the lighthouse. I anchored in a developing Seabreeze with the wind blowing from the headland and roughly parallel to the isthmus. This gave me a fairly predictable low wind speed developing to as high as 35 knots at each scope (and, very importantly, it was warm and sunny). I agree that doing some work with chop and swell would be useful. My ideas on the importance of waves action has grown - initially I would have discounted swell but you will note that the miximum snatches I was getting was only 650kg and 'even' a well set Delta (of the right size) will hold that. However our, copy, CQR dragged at much lower speeds and I've seen Delta and Bruce dragging at much lower windspeed - so there is another, or other, mechanism. I favour a combination of yawing and chop[/swell. There is also my idea that the vibrational movement of the yacht itself., transmitted along the rode, reduces shear shear strength of the seabed round the anchor. Certainly when I touch an anchor it twitches - so if the shear strength is reduced (as happens when you twiddle a trowel in damp concrete), then the measured hold of anchor is higher than 'reality' (because the shear strength of the seabed is actually lower - because its constantly modified by the anchor). This twitching is reduced with a snubber - it does not transmit so well, if at all.
The problem is developing tests that differentiate the possible mechanisms - and accepting there might be something else going on that we have not thought of.
The reassuring thing is that modern anchors are better - maybe not because they hold more but because they are deeper they resist some of these unknown characteristic. If depth is a key then anchor designers might be better to focus on better diving ability. Viking is offering that - but maybe sacrificing something else (that we do not know about). Izi Kalvo's use of a 10kg anchor is going to go some way to, maybe, answering some of the unknowns - because if he drags he'll change and be using a 15 or 20kg model - and we will find out. My tests on the 10kg model clearly show the Viking sets very quickly and develops more than enough hold for a 43' Jenny. Because it sets so well I used it when I did my investigation of shackles angles that I referred to in a slightly easier post.
I have a Viking 10, the same as his, but we have more windage and lightweight chain. We cannot conveniently use the Viking because the roll bar fouls our bow roller assembly. But when we anchor somewhere where the conditions are 'right' we'll be trying it. We need a combination of decent wind and chop - be patient!
If anyone has any input on testing, issues raised etc - I'd like to know (as would others who test, including (I guess() Izi Kalvo) as this testing can be onerous and getting it wrong means we need to do it again
. Jonathan
john_morris_uk
Well-known member
The video was interesting but he speaks as though he is an authority whereas the only authority he has is his relatively recent cruising experience. The experience definitely counts but some of his sweeping statements are highly questionable imho.
His claim that the packed sand bottom was the perfect test sight. It’s one test sight but I’d like to know about an anchors performance in multiple types of bottom. Hard sand and clear water is good for photography but it’s only part of the story.
His extolling the virtues of the anchor turning without barely moving was over egged as far as I’m concerned. In real life an anchor will turn and nudge against a buried large stone and trip over and reset itself and on board you’ll never know.
There were several other sweeping generalisations that I was disturbed by and he needs to caveat his claims a little more.
His claim that the packed sand bottom was the perfect test sight. It’s one test sight but I’d like to know about an anchors performance in multiple types of bottom. Hard sand and clear water is good for photography but it’s only part of the story.
His extolling the virtues of the anchor turning without barely moving was over egged as far as I’m concerned. In real life an anchor will turn and nudge against a buried large stone and trip over and reset itself and on board you’ll never know.
There were several other sweeping generalisations that I was disturbed by and he needs to caveat his claims a little more.
geem
Well-known member
Deleted due to YBWs forum software doing weird things
john_morris_uk
Well-known member
I think you’d pressed the quote button. Do you want your text back?
