The Kiwi Rocna Anchor - odd choice for an odd bloke?

Quite an interesting video and at first sight convincing. Strange however that the competitors they demonstrated were all pretty old technology. No sign of Delta, Spade or Fortress. I think that may say something about the credibility of the sames pitch.

I wait with interest for the response from M. Hylas,
 
Re: Fire extinguisher

After watching the Rocna video online I think I will fit a fire extinguisher up forward do douse the electric windlass when it goes up in smoke trying to break out the Rocna.
 
Re: Delta and Spade compared

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Strange however that the competitors they demonstrated were all pretty old technology. No sign of Delta, Spade or Fortress.

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A Delta and Spade can be seen in the background of the video but I guess they were not so easy to lampoon visually to classical music as the old designs.

However if you study this results page the designs you mention are compared.

http://www.rocna.com/main.php?section=real&chapter=testing&page=0

The Delta and Spade are up there with the Rocna in terms of holding power, but the Rocna wins the setting test by a clear margin.
 
spade is listed in the results graphs but not shown on the video, as is the delta (fixed plough I assume).
both almost match holding but take a whole extra metre to set on average (and in their test conditions!)
Both Delta and Spade seem very well priced against the Rockna at first glance...........
I am trying my first anchor other than a Claw/M/Bruce next weekend - not because I have had any problems but I have bent the thing and want to get it sorted!
 
As an example of how manufacturers manage always to get their product coming out top, have a look at this

I generally find that if I put a load on my anchor before it has set it will skim over the sea bed but give it a chance to dig in and it will hold no matter what.

It looks as though the Rocna is a very similar configuration to the Spade though the roll bar makes it look more like the Bugel I wonder if it has the same problem as the Spade in soft mud, i.e. digging out a conical lump of mud that effectively makes it plough-shaped!
 
Rocna anchor - seems pretty good, but looking at the film it seems a bit fixed - they have much softer sand than the others.
 
yep had seen that test result before - amazed me they were so proud that their winner, at 53lbs, managed to do better at setting and holding than the others, including 17lb steel ones!

Oh well - it's good fun anyhow.
 
I am in NZ and have never seen one fitted to a keel boat - in fact I have only seen them for sale in small boat retail outlets (open to small decked MoBo's) - but no doubt there are some on large sailboats, but they certainly are not common.

I wonder if others looking at the video noticed this - it seemed to me that when they dragged the other anchors on the beach they started out with the anchor on moist sand, whereas with their own anchor it seemed to me that the sand was very much wetter. I would be interested if others think that or not (unless I misunderstand, I think Woody alludes to the same thing).

Beach tests can be quite misleading in my view as the sand reacts very differently according to how wet it is. When sand is moist but not fully wetted it is at its hardest (as people who drive on beaches know) as the surface tension of the water between the grains holds them together. When it gets wetter it starts to fluidise as there are no water surfaces between the grains for surface tension to occur on and when submerged it is always fluidised on the surface.

Pulling an anchor on the beach sand where surface tension, such as in the video, is acting is not a relevant test. They may be very fine anchors, but I would not rush out and buy one on the basis of the video.

John
 
Not sure you can actually take this for granted. Fluidised particles act in very strange ways. I won't prompt you on this, but try this experiment.

Take two spoonfulls of cornflour (important, use cornflour, used for thickening liquids in cooking, not normal flour - not sure if same if commonly available in NZ, but very easily available in UK) with one spoonfull of water.

Mix well in a small bowl

You should get a paste which you can scoop up with a spoon, and will flow like a liquid when you tilt the spoon, albeit a thick liquid.

Now try stabbing the spoon into the paste? What happens.

Now try allowing the spoon to sink into the paste under it's own weight?

Now try to pull it out? Quickly and slowly?

Now try sticking the spoon into the paste and pulling up a large spoonfull?

Hopefully the experimental results are that I don't need to describe what happens in each case. Interesting, isn't it?
 
Yes.

But was just being sparing with explanation for differentiating between the cases of sand particles held together with surface tension when partly wetted and those that are fully wetted, and so are not so held, and which I loosely called "fluidised".

Very loosely, in fact, cos things can be fluidised in any fluid, including gases and that is hardly relevant to anchors either. And other things happen which cause fully wetted sand to disobey my loose wording such as close packing due to grain size, etc and can result in firm sand seabeds hard to penetrate /forums/images/graemlins/smile.gif

John
 
Have you tried the cornflour experiment tho? Please do, it was shown to me by a 10 year old whos stand in teacher had shown the class as a practical experiment. Suprised the heck out of me, and explained many things about quicksand etc and may help many understand anchor holding in sand and mud

The 10 year olds version included copious amounts of blue food colouring, which seemed to keep her occupied and amused while she showed her experimental results to me, but as she was learning I didn't object, but isn't necessary to the experiment. I learnt a lot from it, and was impressed by the teacher, apparently newly out of training college. She has a good future in front of her if she can keep coming up with stuff that impresses me! <g>

Especially as the 10 year old was able to explain the results to me, even though not understanding the theory behind it. Poke it hard, and it goes hard, pour it and it's a liquid. Quite advanced undertanding in many ways for that age - usually you get to higher school or uni before you start understanding those concepts.

As for fluidisation, we could go for a 200 post thread on that one? /forums/images/graemlins/smile.gif
 
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As for fluidisation, we could go for a 200 post thread on that one? /forums/images/graemlins/smile.gif

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Please feel free not to, I'm falling asleep already /forums/images/graemlins/smile.gif
 
I did not know that cornflour acted that way until you mentioned it (and I did try it as you suggest). But know the effect as had a little to do with colloids and other suspensions many years ago (eek 30 actually /forums/images/graemlins/frown.gif) as worked for a company into water treatment (especially flocculation) and also food processing where many things, like some sauces, are thixotropic colloidal solutions which behave the opposite, hence we shake the bottle to make them runny to get them out.

Muds/silts we anchor in are thixotropic so not much help there, and sand is, well sand unless very fine.

{Edit: Could add that the thixotropic properties of muds/clays/etc are very important here in NZ as they go runny when shaken in earthquakes so building foundations over such materials - even if well down below the upper layers of the ground - are special; piles or ground removed and backfilled/compacted mechanically or by preloading.}

John
 
Thank you for the report, not what I wanted to hear but I did need that information.

In general I warmed to the whole Rocna presentation, exemplary online promotion of a small single product business. The anchor looks right to me, at distance in profile there is a hint of a Delta but closer up the fluke angles indicate Spade scoop principals are used. Having seen the Bruce and CQR slide along on their sides, I am sold on the stabilizer hoop.

Ok here's the problem. My cruiser-racer has an undersized clip-on bow roller that is not suitable for permanent over the bow anchor stowage. My existing 35lb Delta is too heavy to be slung out through the pulpit and onto the roller each time I drop anchor.

I plan to employ a tip provided by Robin last week. Experiments at the week indicate that with a smaller anchor it should be possible to fit a fender-step shaped fender over the bow and in sheltered water mount the anchor over the bow with windlass tension pulling the tip of the anchor back into the fender.
 
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Having seen the Bruce and CQR slide along on their sides, I am sold on the stabilizer hoop

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probably the last reason not to buy a Bruce, most of the extensive tests have it as one of the best to set and critically reset out there. where it is ulitmately weak is in holding power/kg and holding when the angle of pull moves away from the horizontal (relative to many other designs).
 
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