Knox anchor anyone?

[Bash]

Is this John Knox the chemist? Professor Emeritus from University of Edinburgh?

[Kettlewell]

Is this John Knox the chemist? Professor Emeritus from University of Edinburgh?

Yes, that's him.

[Kettlewell]

Can anyone figure out what red, blue, and black numbers are supposed to indicate in the anchor selection table for Knox anchors?

The product range
To find the appropriate Knox Anchor for your yacht:
Select the appropriate LOA.
Read along to select Tonnage in red, blue or black.
Read up to find recommended minimum Anchor Weight appropriate for winds up to Force 8 and where waves are not excessive.

[Andrew Troup]

I've got an unused 30kg genuine Bruce, zeehag, and I've NO intention of letting go of it.

[Andrew Troup]

OK, I had a look at the Knox tests and I have a couple of 'issues' with them:

1) Like most anchor tests, the test sites were chosen for practicality, and consistent holding.

To me that's perilously close to the reasoning of the guy who looks for his keys under the lampost 'because it's dark over there where I dropped them'.

What I'm saying is: They test where it's easy to get good, tidy results, rather than in the places where anchoring is challenging.

To people like me who are regularly forced to anchor in bad holding, it's of little interest how well my anchor would hold in good holding (and good holding is almost inseparable from the "consistency" which scientific testing requires).

I have NEVER dragged anchor in good holding (unless I picked up an object muzzling the anchor); hence the 'Ultimate Holding Capacity' provided by tests is of virtually no interest to me.
It's like having a car which can do 200kph; the figure is academic when 100kph is plenty for my needs.
I do however need to (metaphorically) get up steep hills with a heavy load, and none of the tests tell me if I have the traction and the gearing and the driveline for that.

Luckily, I don't need those tests, having done my own field testing under realistic circumstances.

2) Infinite (flat) scope: testing anchors this way is indistinguishable from voodoo science, to me. The only time I can see me dragging an anchor at infinite scope is if I'm pulling it up a ridiculously steep slope, or in deep water on ultra-heavy chain.

I had other problems, but these two are enough to stop the show, for me.

The second problem is particularly relevant to why Bruce anchors work well in practice**, when modern test-based theory consistently says they're little better than a fisherman.

** (except in the hands of 'non-sailors' -- or in some cases it's possible that what looks like a Bruce may be a poor copy)

Modern anchors are generally designed "to the test": their designers test them in shallow water, on a flat to infinite scope. Partly because it's easier, and partly because they know that's how boating mags will test them.

Bruce anchors, OTOH, were designed to work best at conventional scope, and well on short scope. Oil rigs do not have the luxury of shallow water or infinite amounts of chain, and oil companies do not read Practical Boating et al.

The strange cyclical pitching behaviour Knox observed, when dragging the Bruce at infinitely long scope, could well reflect something which does not actually happen in practice. This tallies with my personal experience, struggling to set Bruce anchors in very shallow water in greasy mud, even an oversized one (which I just described in the Bigger/Better thread)

In good holding, I have found it's preferable to set a Bruce at relatively short scope (in comparison to what works for other anchors) before dropping back.

This suggests to me that possibly the hobby-horsing behaviour remarked on by Knox (among others) might result from the load being applied at an angle which neither causes nor permits the anchor to behave as designed, ie to set properly in order to hold a load properly.

[Andrew Troup]

Originally Posted by Snowpetrel

Very Interesting, Almost like a modernized roll bar concave danforth! It would have an extremely angle for the pointy bit so it should start to pull in easily.

I would perhaps worry that something (like the chain) could get stuck in the slot. I Guess it would be best to set it properly each time, to reduce the risks of an anchor warp going astray...

But It's very good to see something new on the scene. Hopefully it will live up to it's test results. Thanks for the heads up. Also found this interesting, referring to the loads on a 30 footers anchor in different conditions using Knox's test equipment.

I think that if it does turn out to be an improvement, Snowpetrel may have put his finger on the crucial element: the included angle of each point is only about one-half of what it would be were the flukes to be joined.

I know for instance that the Rocna really struggles with papa rock

It's a sort of blue-grey sandstone or mudstone, which occasionally forms a 'floor' to parts of an anchorage, particularly in NZ's North Island on the East Coast

It is a right b*gger to get an anchor into.

Points are essential to get the digging process started, and the Spade in particular was an attempt to address this. I guess the Manson Supreme tries, too, but it doesn't look sharp enough, to my eye.

I reckon if the Knox points were hard-faced with stainless so they could be kept sharp, it could be a very useful innovation. I like the way the points would not present a great risk to the hull of the boat, because of their proximity to each other.

- - - -

I might be a bit sensitive about that particular issue.

I have a secret weapon, which I built for bull kelp but which is equally dangerous in papa: a massive pick anchor, with stainless palms out of 12mm thick 316 SS, sharpened to wicked edges ending in sharp points. The geometry of the anchor is such that it can sit stably on the bottom, the tripping line being used to lift and drop it repeatedly over the same spot.

At a pinch it could possibly be used for breaking ice.

The weight at the business end is sufficient to drive the point through 5mm aluminium *, so it has no trouble getting into papa.

*(which is a bit of a worry on retrieval - someone has to go over the side with muzzles, if the anchorage is rolly - and my next boat will have the mainboom rigged as a crane, complete with slew)

[Andrew Troup]

A curious thing about the "Scope" section on the Knox Anchor website

The graph shows scope along the top, and up-angle of the rode at the anchor along the bottom.

At 4:1 scope, Prof Knox reckons the latter angle is about 6 degrees.

The inverse sin of 1/4 was nearly 15 degrees when I went to school...


Could it be that Prof Knox is breaking ranks with other New Gen anchor wallahs?

[sestina]

There seems to be a lot of welds in the design.

[Jimbo485]

Originally Posted by Andrew Troup

A curious thing about the "Scope" section on the Knox Anchor website

The graph shows scope along the top, and up-angle of the rode at the anchor along the bottom.

At 4:1 scope, Prof Knox reckons the latter angle is about 6 degrees.

The inverse sin of 1/4 was nearly 15 degrees when I went to school...

Could it be that Prof Knox is breaking ranks with other New Gen anchor wallahs?

Is he making assumptions about the catenary? Is there a footnote somewhere in small print?

[Andrew Troup]

Catenary, according to New Gen doctrine, is a largely mythological construct <G>

[Kettlewell]

All of this brings up the age-old debate of how one could design and carry out an anchor test that would provide useful information for real-world use. It has been debated here on CF before, and of course there is no single correct answer. It is a tough problem, if you think about it. For example, the only way I imagine you could test for anchoring in poor holding ground would be to repeat the tests over and over again, and then average the results over say 100 tests. The other big problem is the veering issue. Some tests--notably JonJo's recently, have tried to get at this, but in the real world there are various odd scenarios that I find to be problematic. For example, after sitting in one spot for day after day of light winds your chain is liable to snake all over the place on the bottom, possibly circling the anchor a couple of times. Then when a big, sudden blow comes the anchor is suddenly tensioned from the wrong direction with a tremendous jerk, and it may come right out in a tangle of chain. There are many real-world issues like this that are hard to address.

So, I can understand why anchor makers go for simple, repeatable tests, that also allow for clear photography. They are worth considering, but they are not everything.

My own personal dislike for Bruce anchors has to do with how many times I have had boats drag into me or nearby while using Bruces. Whether it's the anchors or the owners I don't know!

[JonJo]

Anchor testing costs a fortune. In the 'famous' WM tests of 2005 or 2006 it took 3 days to make 100 pulls. They tested about 8 anchors. used a monster workboat. It would need 3 or 4 people (they had more because they had journos from 3 magazines on board), the report I read suggested they all worked their backsides off (changing anchors, they might have deployed and retrieved by hand).

The end result was contentious - so the monies spent simply generated arguments, that run until today. John Knox did his tests, at his own expense, from a beach in Scotland, unsurprisingly it was near his home. I test in Pittwater and when ever I can travelling up or down the coast. What thanks does anyone get, very little (though the positive comments do suggest some people appreciate the efforts involved). Most comment is one of complaint. - Not realistic, biased, not enough pulls of one anchor in each seabed, did not use, hard, soft, mud, silty, soft over hard seabed etc. Used infinite scope not 7:1, not 5:1 not 3:1 etc etc.

The ultimate insult is that the results are biased in favour of one or a few anchors and the testers have a commercial bias. For example Cotemar suggesting I should be a commercial member. I am completely independent. My results throw up a 'best' anchor, oddly I buy the anchor that comes up best, and I say so. This then leads to accusation of bias and financial interest. Why when I conduct tests over weeks in different seabeds, at different scopes using almost every anchor imaginable would I buy an anchor that is not the best? Why, given the effort I invested, would I not say so?

Is it any wonder people do not test anchors or publish the results - the recipients of the information show minimal gratitude and some go out of their way to belittle and denigrate. One of the opening posts on this thread was to belittle John Knox statements - without having read one of his articles, with knowing anything of his anchor. We have had the comments, CQR is convex, CQR does not work QED. no convex works. With a logic like that no wonder people shun CF (you have noticed all the Australians left and never came back), no wonder some who contribute get shirty.

You, the complainants, reap what you sow.

Magazines are very reluctant to become involved in anchor tests now. Practical Sailor is one of the few left paying for any articles. You need to accept what is possible or accept there will be no testing (except by anchor makers).

Someone - start a thread, anchor testing, between you all come up with a regime that will satisfy your demands, make it commercially feasible (ie forget the 40t workboat) and I for one will try to accommodate. But tell me when you reach the end of the debate, I'm not interested in setting myself up as a punch bag.


Jonathan

Originally Posted by Kettlewell

All of this brings up the age-old debate of how one could design and carry out an anchor test that would provide useful information for real-world use. It has been debated here on CF before, and of course there is no single correct answer. It is a tough problem, if you think about it. For example, the only way I imagine you could test for anchoring in poor holding ground would be to repeat the tests over and over again, and then average the results over say 100 tests. The other big problem is the veering issue. Some tests--notably JonJo's recently, have tried to get at this, but in the real world there are various odd scenarios that I find to be problematic. For example, after sitting in one spot for day after day of light winds your chain is liable to snake all over the place on the bottom, possibly circling the anchor a couple of times. Then when a big, sudden blow comes the anchor is suddenly tensioned from the wrong direction with a tremendous jerk, and it may come right out in a tangle of chain. There are many real-world issues like this that are hard to address.

So, I can understand why anchor makers go for simple, repeatable tests, that also allow for clear photography. They are worth considering, but they are not everything.

My own personal dislike for Bruce anchors has to do with how many times I have had boats drag into me or nearby while using Bruces. Whether it's the anchors or the owners I don't know!

[Kettlewell]

JonJo, I hope you didn't think I was being critical. I really appreciated the reports on your tests I have read, and I have downloaded and printed them out to keep. I was just trying to point out some of the difficulties in coming up with scenarios that really do mimic the real world--if it were easy and cheap, everyone would be doing it!

One factor that often gets overlooked, IMHO, is something I have a professional interest in. The WM tests being a prime example. The reporting of what information was gathered was incredibly muddled and full of errors and omissions, to the point almost of absurdity in some cases. I discussed this in private with some of the participants and they admitted major problems in this area. Here's my plea for magazines keeping professional and experienced editors on staff who can write up a test so that the results make sense.

[JonJo]

Kettlewell,

Sorry I was actually agreeing with what you said. 'We' do the best we can but our ideas and test methods are sometimes limited by our lack of imagination (but more often by what is feasible and/or what we can afford). Its too easy to say 'we want test from a real yacht not this rubbish from a tugboat or a shore based winch'. Tell me how to do it! And then find me a location with these 'difficult' seabeds.

But being accused of commercial bias without foundation is simply not helpful.

I agree with a previous post - we do tend to concentrate on 'decent' seabeds - but this is because that's what we've got. We, that's Sydney, do have an anchorage with a reputedly 'hard' seabed - but its 70nm away (Port Stephens), not somewhere I can nip out to on a sunny afternoon! We do have soft/ muddy seabeds, but they are organic muds and probably not typical. We have seabeds that are small rocks and pebbles but the nearest ones I know are 500nm away, 100nm from the nearest house - yes I use them but not somewhere I can use as a subject for testing without some really serious thought (and a lot of time). So, sadly,many results are from sand, of various types and thin weed (sea grass) but we, (no anchor makers in the 'we') actually try our best.

Jonathan

I'm labouring on the refurbishment of a 50' wooden cruiser racer (bits of it the subject of future articles), I also do all the mast work. In return for my labour I get labour for my anchor testing. In the fullness of time I'll also gain access to a, the same, 50' yacht to replicate some of the work I had done on our catamaran.

[Andrew Troup]

Tricky real world issues (like the one Kettlewell mentions) are almost as numerous and varied as sailors and locations, and I personally don't think it's realistic to expect tests to address them.

Perhaps the hardest real world issue is that different anchors require different methods to set them. It's hard to imagine a test procedure which would do justice to anchors which (say) do not respond well to simply being winched into the bottom and immediately exposed to full load - in cases where those same anchors have other virtues which are not matched by the anchors which do perform well under this regime.

On the other hand, testing at realistic scope and on bottoms which are permanently underwater, and other such basic elements, seem to me to be minimal prerequisities if the tester expects their tests to be taken seriously.

I don't complain about tests, because I don't pay for them, and as I say above, I don't need them. I do think that those who treat test results as some sort of scriptural truth are doing themselves, and the discussions they join, a disservice.

When discussing claims made for various anchors, I'll certainly take issue with the test methodology which lies behind those claims, if I think I can see problems.

The moment Prof Knox started selling anchors based on his tests, it's inevitable that his claims would come under more challenging scrutiny. A formerly disinterested expert witness would not expect the same freedom from criticism once they signed a contract to do forensic work for the police, or for a particular defendant.

Incidentally, and it's not related to my point: I'm willing to bet Peter Smith is not exactly delighted that Prof Knox has done an 'end run' around the Rocna, and is linking to the Rocna website in support of his competing product!