Rocna Mk II

[ranger58sb]

Originally Posted by malbert73

I wonder though- I believe part of my personal Rocna failures in soft mud were due to the smaller rollbar being less effective in orienting the Rocna tip down- consistent with Panope’s video showing a Rocna stably upside down

Originally Posted by Dockhead

My experience with the Rocna in soft mud is the same as yours. Basically, it doesn't work in that kind of bottom -- forms a ball of mud around the anchor which can't set.

Originally Posted by Anders

That's strange cause we anchor a lot in soft mud and it's what I consider the real strength of the Rocna.
It dives deep into the mud until only the short floating rope is seen. It certainly can bring up a lot of mud and often needs to be dragged in the water for a while.

The original rollbar Rocna didn't do all the well in the Fortress "Chesapeake soft mud" tests, either.

I've no experience here with that one. Danforth, good. Fortress, good. SuperMAX, good. Delta, bad.

We did the initial splash of our new Vulcan a couple weeks ago. Seemed to work pretty well, although we had dead calm weather so it wasn't much of a test. Then it took about 40 mins to get the mud out of the chain links and off the anchor...

The new Rocna looks to me (as others have said) like a Vulcan with a thinner diameter, larger curve rollbar.

-Chris

[Anders]

Originally Posted by ranger58sb

The original rollbar Rocna didn't do all the well in the Fortress "Chesapeake soft mud" tests, either.
-Chris

I'm not aware of that test but the results would not surprise me if the manufacturer of Fortress paid for or organised the test.

[DumnMad]

Too many variables to reach simple conclusions.
Deep mud or shallow mud ? Penetration depth is very important in soft ground.
Holding power triples when double the depth and much more still if the mud gets more dense with depth.
Also test comparisons from 15kg anchors will be different from those done with 40kg anchors. The heavier ones have more weight on the same shaped tip which is better for getting started.
Also it appears plate thickness is doubled when you double the area of the fluke so you get triple the anchor weight if doubling the fluke area so a larger has more likelihood of sinking deeper.

[ranger58sb]

Originally Posted by Anders

I'm not aware of that test but the results would not surprise me if the manufacturer of Fortress paid for or organised the test.

Sure, there's always that. OTOH, a Fortress (or Danforth) has pretty much always worked well here anyway... so the actual "winner" could well have been a foregone conclusion.

It was the rest of the results that were useful for me... since we already know about Fortress, already use those as either primary or backup, and since I was paying attention to having another viable anchor immediately available.

-Chris

[Dockhead]

Originally Posted by DumnMad

Too many variables to reach simple conclusions.
Deep mud or shallow mud ? Penetration depth is very important in soft ground.
Holding power triples when double the depth and much more still if the mud gets more dense with depth.
Also test comparisons from 15kg anchors will be different from those done with 40kg anchors. The heavier ones have more weight on the same shaped tip which is better for getting started.
Also it appears plate thickness is doubled when you double the area of the fluke so you get triple the anchor weight if doubling the fluke area so a larger has more likelihood of sinking deeper.

Good points.

The larger the anchor of the same type, the LESS fluke area it has for the same weight. That's apparently why larger anchors seem to perform so much better than smaller ones. Note the widespread (probably unscientific) belief in some "magic" effects above 100lbs. Probably unscientific, but I've experienced it!

That's why I think ballasting an anchor with lead is really good for its performance. Makes it "denser" so easier to sink into the mud or penetrate other kinds of seabed. Also makes it balance better. Plain steel is not hugely more dense than wet sand (maybe 4x); lead is better at about 6x; tungsten would be awesome at something like 13x -- would just sink right through it.

I always thought an anchor with a sharp tungsten tip (more than double the density of lead, and hard to boot) would be the ultimate anchor.

Ultimate holding power once set is determined by fluke area and geometry; very little by weight (although that has SOME effect). But setting behavior is very much determined by weight, and by "density". So you'd want an anchor with enough fluke area to give you holding power with good reserves even in poor seabed, but then within that fluke area as heavy as possible. Anchor handling is the limitation on size, but much more by fluke area (and shape, and presence of any roll bars) than by weight, at least for those of us with powered windlasses. The anchor is normally a relatively small part of the weight of the ground tackle, so doubling the weight of the anchor is not generally a problem. On my boat, for example, the chain weighs 330kg or a third of a metric tonne. The difference between a 45kg and a 90kg anchor makes little difference in the work the windlass does. But I can't fit any 90kg anchor I know of in my bow roller, so I'm limited to 45-55kg.

[malbert73]

All good points DH, and indeed ballasted anchors like Spade seem to perform really well. And that’s the great thing about Noelex and Steve/Panope’s work- which shows actual performance not just theory. And some rollbar anchors perform at the top.

My theory is that lack of ballast makes the fluke thinner and therefore it’s easier to penetrate the seabed. And, the Mantus M1 (yes I’m an unabashed fan) has, according to Panope, one of the highest tip weights when in setting position due to the wide rollbar.
So, a lot of factors combine together to make an anchor that performs well.
Since I spend some time in soupier mud, I avoided the Spade because it’s not quite as strong in those conditions

[s/v Jedi]

We need an anchor with a lithium powered, active carbide tip

[AKA-None]

Originally Posted by s/v Jedi

We need an anchor with a lithium powered, active carbide tip

Ahhhh so it drills into the substrate cool idea when will it be available

[Panope]

Originally Posted by s/v Jedi

We need an anchor with a lithium powered, active carbide tip

Even better would be an anchor made of variably molten metal, like the shape shifting villain in the Terminator movie.

[Dockhead]

Originally Posted by malbert73

All good points DH, and indeed ballasted anchors like Spade seem to perform really well. And that’s the great thing about Noelex and Steve/Panope’s work- which shows actual performance not just theory. And some rollbar anchors perform at the top.

My theory is that lack of ballast makes the fluke thinner and therefore it’s easier to penetrate the seabed. And, the Mantus M1 (yes I’m an unabashed fan) has, according to Panope, one of the highest tip weights when in setting position due to the wide rollbar.
So, a lot of factors combine together to make an anchor that performs well.
Since I spend some time in soupier mud, I avoided the Spade because it’s not quite as strong in those conditions

I've heard nothing but good things about the Mantus, but I've never tried it myself.


Your theory about fluke thinness sounds right to me. Why a high density ballast material like tungsten -- which in one of the impure alloys is not all that expensive -- would be really great for this. All the more because tungsten is very hard and wouldn't need to be encased in steel like lead does.



Soupy mud is a special challenge. My various Spades over the years have done better in that than my Rocna etc., but I tend to go for the Fortress in that kind of bottom.

[FlyingScot]

Anyone know where to preorder a 33kg Rocna MKII in the USA?

The AU site mentions an expected date that is already past due. Any idea of actual shipping dates?

[DumnMad]

Originally Posted by Dockhead

Good points.

The larger the anchor of the same type, the LESS fluke area it has for the same weight. That's apparently why larger anchors seem to perform so much better than smaller ones. Note the widespread (probably unscientific) belief in some "magic" effects above 100lbs. Probably unscientific, but I've experienced it!

Makes sense to me, soil friction stops lighter anchors sinking to a more effective depth. Thats why Panope's comparisons for 15kg are no help for assessing the effectiveness of your 100lb anchor. The light weight anchor is floating in the soft mud while the heavy one is more likely to overcome soft mud friction and dig into the more dense/sticky mud.

Ultimate holding power once set is determined by fluke area and geometry; very little by weight (although that has SOME effect).

No, ultimate holding power is proportional to fluke area x soil density/friction.
Same area of fluke but twice as heavy will sink deeper into stronger soil.

Talking mud, silt and sand of significant depth. Shallow sand on hard bottom is another story.

[Dockhead]

Originally Posted by DumnMad

No, ultimate holding power is proportional to fluke area x soil density/friction.
Same area of fluke but twice as heavy will sink deeper into stronger soil.

Talking mud, silt and sand of significant depth. Shallow sand on hard bottom is another story.

I don't quite see what you're disagreeing with. I agree with what you wrote.

[DumnMad]

Originally Posted by Dockhead

I don't quite see what you're disagreeing with. I agree with what you wrote.

A minor difference. In agreement with your "magic" effects above 100lbs I just meant ultimate capacity is not fluke area alone. The heavier anchor of same fluke size will have higher ultimate capacity because extra weight helps the fluke sink further into lower more dense soil with higher shear capacity.

[Dockhead]

Originally Posted by DumnMad

A minor difference. In agreement with your "magic" effects above 100lbs I just meant ultimate capacity is not fluke area alone. The heavier anchor of same fluke size will have higher ultimate capacity because extra weight helps the fluke sink further into lower more dense soil with higher shear capacity.

Ah, got you now.


Yes, that's kind of what I was saying. Maybe one way to say it is like this: Ultimate holding power is not just a function of fluke area, but fluke area and the quality of the soil it's in. A denser anchor (more weight per unit of fluke area) sinks in better (sharper fluke helps here too) and is more likely to be in better soil. Plus a denser anchor is easier to set so more likely to be set in the first place.


As anchors of the same design get larger, they gain weight faster than they gain fluke area, so become "denser", which is a good quality.


Another reason why it's absolutely rational that cruisers strive for bigger anchors. They get a lot better as they get bigger. Per Steve Dashew also.