Anchor Loads - Which size of swivel?

[Tim Good]

You can see the fluke is only just starting to bury. At this stage the anchor does not have a lot of grip. However, the end of the shank is already buried. If you hinder the end of the shank burying, you also hinder the fluke from burying.

I think you have picked up on a very good point that I have not previously considered.

I suppose the trouble is that with my anchor having a round hole the largest rated bow shackle I can use on an 10mm chain is rated to around 1.5T WL. See the link below for a fairly standard rated galvanised lifting shackle.

http://www.safetyliftingear.com/File/Download/152

In my case I have 13mm between the links of a 10mm link. The pin has to go through the anchor as the hole is round which means the dimension "A" is what will go through the chain link. In my case the max I can have is a 1.5T rated shackle. On so that equates to a 9T breaking load which I suppose is ok but because it is fix by the pin in the anchor it could be taking loads on the side rather than rotating in the direction of pull like a bow shackle should do.

That then takes us back to upping the site of the shackle and back to square 1 if we are taking your points above as significant... which I think they probably are.

 

[Neeves]

The three links of chain to reduce the side loading on the swivel is very sensible. When doing this, I have noticed a lot of people use thicker chain for the three links as you have done.

This has advantages in allowing the use of stronger (but bulkier) shackles. The added weight is minimal, but I wonder if it is best practice.

Most modern anchors bury in the end of the shank (where the thicker chain and larger shackles will be) very early on. I am not sure what anchor you have, but this photo of a Delta illustrates the point:

You can see the fluke is only just starting to bury. At this stage the anchor does not have a lot of grip. However, the end of the shank is already buried.

If you hinder the end of the shank burying, you also hinder the fluke from burying. This happens very early on in the setting process so making the end of the shank bulkier will have some effect on most sets.

The use of thin wire rope close to the anchor has been suggested as a means of improving anchor performance (one manufacturer even supplied wire for this purpose with their anchor). I think this is probably overkill. Chain is more reliable than wire rope. However the message is be careful not to make the chain and shackles, close to the anchor shank too bulky.

12mm chain is quite a bit bulkier than 10mm and larger shackles add to the drag. It is difficult to know the practical effects of these sort of differences, but in hard substrates I suspect it will make some difference.

These are only small details, but if you can use 10mm chain next to the anchor with smaller shackles and still have adequate strength, I think this is better.

There is an article in Practical Sailor from a couple of years back with some quantification. But you are correct - anything, shackle, swivel and chain are a hindrance to diving, as the PS article pointed out. They also illustrated the fact that the shank and toe of the anchor 'dive' or bury together. However any retardation of the shackle end of the shank from burying does not stop the toe and fluke from engaging and burying, however it will reduce the maximum hold possible. Most anchors never achieve their maximum potential of diving and as you illustrate in your images many anchors are not buried very much at all - but they still perform.

None of this is original - the US Navy have programmes to identify to what depth anchors will dive (be buried) based on strength of the seabed, chain size, anchor design/perfomance etc. The oil industry use thin rodes for the simple reason - thicker rodes retard anchor penetration.

By changing rode thicknesses significant differences in anchor perfomance can be achieved.

Most national marine authorities will allow the use of wire rodes, retained on a drum, suggesting they think they are safe. However most vessels in survey are scrutinsed yearly, unlike leisure vessels.

Jonathan

 

[Neeves]

The link you provide is of shackles with pretty average specification. I'd recommend you look at the Crosby website - you will find a much greater cross section of shackles to much higher specifications.

Jonathan

 

[NormanS]

Thanks - if only my clutch were that sensitive. Maybe I have the wrong windlass?

The windlass does that all by itself and dumps the chain overboard with me scrambling about looking for a winch handle to lock it off! Its one of a few reasons I retrieve the anchor and my wife deploys.

Jonathan

Sorry, but I'm not sure what you mean when you say that "the windlass does that all by itself and dumps the chain overboard.........."

Is there something wrong with the windlass?

 

[vyv_cox]

I rarely disagree with Vyv but I must say, having the Bow bit of the shackle through the anchor makes more sense with respect to loading from different directions.

I really cannot see that it makes any difference so far as loading from different directions is concerned. The chain will swing around the bow as easily as the bow will swing around the anchor. A D shackle is theoretically preferable to a bow for a single attachment although not different so far as strength is concerned.

 

[Neeves]

Sorry, but I'm not sure what you mean when you say that "the windlass does that all by itself and dumps the chain overboard.........."

Is there something wrong with the windlass?

The clutch is simply how tight the gypsy is adjusted, which is done with a winch handle. If its too tight there is no slippage, if its loose the gypsy will not hold the chain. The difference between tight and loose is not much. If too loose when a load is taken, say wave, then the clutch can loosen by itself and all the chain run out, unless you stop it.

Jonathan

 

[Tim Good]

The link you provide is of shackles with pretty average specification. I'd recommend you look at the Crosby website - you will find a much greater cross section of shackles to much higher specifications.

True to an extent but the Crosby ones which are rated higher: i.e. their allow versions like the G209A does show higher WL's but then they are rated at 4.5x ultimate strength rather than 6 times. When you compare ultimate strengths they are very similar. I spoke to them about this and they said that the Alloy ones were given high WL due to specific job requirements in the States and now they are standard production. So most of their stuff is x6 factor apart from the alloy ones which are x4.5. For example this:

http://www.liftingsafety.co.uk/product/alloy-screw-pin-shackles-2376.html

Bottom line is that either crosby or the standard rated ones have an ultime strength of 8+T on a shackle to fit in a 10mm link which I think is around the same as 10mm chain so you are probably right in terms of downsizing and using 3 links of 10mm chain and a smaller shackle to reduce the diving resistance of the anchor.

The least resistance would be to put my swivel directly on the anchor but then we're back to square one again

 

[Neeves]

You are obviously looking into this with caution.

I've just been playing with some 3/8th shackles, 7/16th pins and 8mm chain for another investigation.

The pins are all different sizes, some fit some 8mm chain, some do not. They only vary in size by a small amount but its enough to fit, or not. So - metric chain varies, slightly, imperial shackles also vary, slightly. So check and check again.

As far as I can make out many bow shackles (and 'D shackles) are actually made to imperial sizes and then given a metric designation which only complicates the issue.

Historically Crosby shackles, those G209A Alloy models were de rigour and quoted all the time on Cruisers Forum - the Peerless and Campbell shackles (at least one, maybe both) are made to a 6:1 safety factor are a better buy - but I do not know how you source them in the UK. I prefer the Peerless range Peerlift, because they have a greater range of sizes - but this is not much use if you cannot buy them! I'd be emailing them both for advise.

I stlll question whether you need the swivel, at all - but something else to do is to extend the amount of chain between the anchor and swivel (it depends on where your windlass is). If you just want to ensure the anchor arrives at the bow roller the correct way round then a bent link/banana/boomerang (Anchor Right in Oz have some in stock - send another email!) is the way to go. Like the oscallati device but without the swivel.

If you have problems with contacts at Peerless, Campbell or Anchor Right send me a PM.

Jonathan

 

[NormanS]

The clutch is simply how tight the gypsy is adjusted, which is done with a winch handle. If its too tight there is no slippage, if its loose the gypsy will not hold the chain. The difference between tight and loose is not much. If too loose when a load is taken, say wave, then the clutch can loosen by itself and all the chain run out, unless you stop it.

Jonathan

Mine is a Lofrans Tigress 1000, and I put some grease or Coppa-slip on the cone faces, and I find it quite manageable to adjust the three-fingered nut, so that instead of burning out the motor in the event of overload, the clutch will slip.
I have certainly never known the clutch to slacken off itself, and let the chain run out uncontrolled. If it did, I would be looking further in to it.

 

[MM5AHO]

My new Knox anchor has arrived, so I'll be really interested in its performance compared to the CQR that's been in use since the boat was new 41 years ago or so.

 

[Neeves]

Geoff, we can compare notes. On a recent trip to the UK and the Med I picked up a 13kg Knox for test purposes. I'll be giving it back when I finish. I'm only just back in Oz but it looks well built and has some surprising and interesting features. I had thought that the toe had been joined so that the slot did not collect debris - this was incorrect as mine is still 'open toed'. The little comment I have read, primarily on YBW, has so far been favourable. You are sadly running into winter so I might get more chance of use before you.

Jonathan

 

[MM5AHO]

Yes, my Knox also looks well built, and mine also is "open toed". Being a galvanizer I can tell that it has either been not recently been galvanized, or galvanized and not passivated (tell by the shininess and patina development stage), I suspect from a stock, and from that I'd guess made in batches, but that's speculation. It came from store in a family members business I understand, and as a result had a sprinkling of aluminium flake on the packaging.
I'm surprised at how small the hole in the shank for the chain connector is.
I hope to fit tomorrow, and might even get a chance to test it, but if not, then the following weekend for sure.

I'm surprised how little marketing is done for this anchor. Mine is also 13kg.

 

[Neeves]

This is developing into real thread drift.

The slot appears to be 1/2" or 13mm and as you imply will be difficult to fit a 1/2'or 13mm bow shackle. It comfortably takes a 3/8" gal bow shackle (and a 7/16th" pin) and will also take a 7/16" stainless bow shackle (I happen to have one). I had assumed the 13kg anchor was focussed at yachts with 8mm chain - but with 10mm chain (which should take a 1/2" bow shackle) there might be an issue. I'm no expert on galvanising so bow, with humble respect, to your knowledge. I had checked and it has an extraordinary thickness of gal, higher than anything I have ever measured (I have not measured much and mostly chain and anchors). Superficially this is good - but I wonder if 200 microns +, I'm getting readings of slightly under 250 microns on the flat, might be brittle, lack adhesion and be flaky. Time will tell - but its something I would be looking at given its so thick.

I too am puzzled at the total lack of marketing. It has all the right backing, a highly credible developer and claims of exceptional holding capacity, for its size (better than any of its peers). The few reports I have seen have all been good. Yet its almost unknown, even in the UK and stocked by too few distributors.

Jonathan

 

[MM5AHO]

Continuing the drift...

I hadn't measured the thickness of the galv (will do so tonight). It didn't look overly thick.
If it is 200-250u thick, that's a problem as brittleness of the coating can become a problem and lead to flaking of the top layer or two of the galv.
While we have about 40% market share of the galvanizing in Scotland, we don't do these anchors, and I don't know who does. (though looks cosmetically / aesthetically good)
The lack of marketing of the anchor suggests low volume anyway, so not such an attractive prospect!

The fluke reinforcement (underside) is interesting, but seems a good addition.

 

[Neeves]

The undersole reinforcement is fascinating - I have never seen anything quite like it, in an anchor. Very original, though simple. Integrating the roll bar, not a fan of roll bars, into the shank is also sensible.

I'll be interested in your gal thickness measurements.

The market must have thrown its hands up in horror when the first Bruce anchors were introduced and then I'm sure Delta was also a pretty boring prospect originally.

Jonathan

 

[Tim Good]

Ok well since we're skitting all over the place here is the Kong avec 3 links just arrived. Now I know the clearance in the links I can order my Crosby G-209A to suit.

Since I have diving gear on board, I may report back at some point with a comparison of shank burial. Maybe the difference is negligible but I am curious.

 

[MM5AHO]

Knox galv thickness: measured and found to be 180u minimum and up to 290u at thickest (on the shank).
ISO1461 says that this should be minimum 85u. Its generally double the minimum. No sign of brittleness though. I think this is probably a result of the steel composition but don't yet know what that is. (I'll measure that some time too).
Without even getting it in the water I'm getting a good feel from this new anchor.

 

[Neeves]

Mine was 200 micron under the fluke, 240 on the side of the shank but 80 on the cut surface of the shank edge. I decided the shank edge was an abberation. I might take some more readings now that I know my data is about right. I believe the shanks is made from a Corus 900 MPa steel (I think John Knox told me this - but maybe its on the website - its not something I could have dreampt about) but do not know what the fluke is, I'm guessing (I know one should never guess) something around 350 MPa. But the fluke looks very robust, whatever its made from, with that web of steel underneath,

I'm pleased you are achieving similar gal thicknesses - it means my data, rank amateur, are about right.

I also agree the gal 'looks' good. It is largely very smooth, looks even (does not actually look thick) but does have a patina of age (not that this is negative).

Jonathan

 

[noelex]

Since I have diving gear on board, I may report back at some point with a comparison of shank burial. Maybe the difference is negligible but I am curious.

That would be great.

I think the difference is going to be small and will not be easy to detect. However, anchor performance is the most vital factor that we need to optimise. The risk of an anchor losing grip and dragging is much higher than the risk of breaking a swivel.

So a small difference in anchor performance will have a correspondingly greater impact on our risk of ending up on the rocks than even a large change in the risk of breaking a swivel.

Ideally both goals should be achievable, that is a near unbreakable swivel without any negative effect on anchor performance.

 

[noelex]

One aspect in considering the ideal anchor connection solution that is rarely mentioned, is the risk of the attachment jamming and producing an unfair lead.

Even a simple shackle can sometimes jam and lock in the slot in the anchor shank in such a way that the chain is leading from the anchor in an unfair way.

So if the shackle can get jammed in the slot in the anchor shank, the chain and therefore the force on the anchor may be from one side of the shank, or be higher or lower than normal.

The shackle will be less strong if it becomes jammed like this, but of far greater significance is the anchor performance may be significantly be affected by this off-centre pull, to the anchor may only set very poorly.

No matter what connection you have between the chain and the shackle, it is worth trying to pull it from different directions to see if there is any risk of the connection jamming in place. When anchors are first dropped, the chain pull can come from all sorts of weird directions, as this photo shows. It is important that the components cannot become jammed in place. A simple change in the design of shackle used will usually fix the problem.