How good is the Rocna?

[Panope]

I agree with Dockhead. ANY repeat ANY amount of air trapped in the shank will help in righting the anchor in some small way.

My Spade anchor shank is open only on the very bottom and will therefore trap air unless the anchor turns upside down. The volume of trapped air will decrease (due to increasing water pressure) as the anchor descends in the water column.

In my rather extensive video testing of anchors, I noticed that the anchors (including the spade) landed and stayed upright virtually every time.

So, I would say this factor provides a benefit to the Spade anchor, albeit a small one.

Steve

[Kenomac]

Originally Posted by Spade Anchor

A ship has a whole lot more "trapped" air. To have any ballast effect the shanks inside hollow area would need to be at least 4x the size of the metal. So if the shank weighed approximately 20 lbs than it would need a hollow area of about 3ft by 3ft and at least 3ft long. That would be for a minimal effect.

The Spade anchor is a 3 piece design that is hollow and not sealed.

Sorry but you're wrong. I'd estimate the total trapped air on our 45kg Ultra to be approximately the same volume as two medium size balloons or the size of a basketball. Ever try to force a basketball underwater? It takes a significant effort. So yes, without a doubt the Ultra shank has buoyancy unlike the sheet metal shank on a Spade.

[TheThunderbird]

As discussion is focusing on the merit of a lighter shank, let me ask you all:

What is the exact function of the LENGTH of the shank!?

I mean, couldn't it just match the strength of the chain (X times, if you concede..) and just be much shorter than it actually is!?

The til penetrates, the flanks hold on, ... what is the shank for, orher than stowing the anchor on deck and connecting to the chain.

Sorry, but i miss a convincing answer up till now

PS I am growing dissatisfied with my original 75#CQR, which slipped twice (once in a deeper sea bottom..) with NO noise, no jerks, no apparent reasons (25kn, no waves).
My confidence in it is minimal

[pcmm]

Originally Posted by TheThunderbird

As discussion is focusing on the merit of a lighter shank, let me ask you all:

What is the exact function of the LENGTH of the shank!?

I mean, couldn't it just match the strength of the chain (X times, if you concede..) and just be much shorter than it actually is!?!?

The tip penetrates, the flanks hold on, ... what is the shank for, orher than stowing the anchor on deck and connecting to the chain.??

Is there ANY case when it has to work as a leverage? On retrieval, maybe!? So, why putting such a large % of the weight in a once-in-a-while secondary function!?

Sorry, but i miss a convincing answer up till now

PS I am growing dissatisfied with my original 75#CQR, which slipped twice (once in a deeper sea bottom, once on a weedy one..) with NO noise, no jerks, no apparent reasons (25kn, no waves).
My confidence in it is minimal now, just a weight-anchor

Where do you get that a large percentage of the weight is in the shank?that's just incorrect (typially I'd guess that maybe 25% at most of the waight of the anchor is in the shank). the shank, aside from connecting the change to the fluke of the anchor determines the angle at which the fluke penetrates the bottom. This is a critical function. the shank neds to be immensely strong as it acts as a lever arm when the boat swings on the anchor. It has to be able to twist the fluke in the bottom without twisting itself.

[TheThunderbird]

@ pcmm
My point is about a shorter shank, not a weaker one.

On CQR, and other anchors design, the section is designed for stronger resistance on vertical bending (eg retrieval) and less on lateral (CQR being almost zero-stressed, as it's pivoted)

Yet, i appreciate that a shank may keep working on the anchor, now and later, to a benefit :-)

[noelex 77]

The technique of adding buoyancy to the anchor is an interesting one.

The discontinued Hydrobubble anchor used this to apparently great effect (according to the anchor tests).

I think we will see anchor manufacturers using this in future models as a means of enhancing anchor performance. No, I don't mean a floating anchor , but rather some buoyancy in the shank or in the roll bar will help the anchor performance.

If the Ultra shank is sealed it will certainly be enough to produce a noticeable effect. It would be nice to confirm if it is truely sealed. The original Ultra had no bracing webs in the shank and it is hard to imagine the stainless walls are strong enough to withstand the pressure at depth. Even at 10m the pressure is around 30Psi. If the anchor dragged into deep water it could be at the full depth of the chain. At 100m the pressure is around 160 psi. To put this into perspective the welds of stainless fuel/water tanks are normally tested at around 3-7 psi. Tank walls have a much bigger surface area (critical to the total force). I think it is sealed, but it would be nice to get some confirmation from Ultra.

The Spade has a fabricated shank, but it is open. The anchor normally drops reasonably nose down when released and then tips over on its side to set so it will lose some air. In addition, the flat sides (as opposed to the convex sides of the Ultra) do not leave much much interior volume for air anyway.

See this photo of an obliging Spade owner who drilled a couple of test holes so we could peer inside. You can see in the second photo that there is not much interior space between the shank sides. This gets a little greater as you move towards the shank top and fluke, but less towards the bottom and anchor attachment point.





So I think the retained trapped air volume in the Spade shank will be small, but every little bit getting the balance of the anchor correct is a help and think it probably has a slight, but useful effect.

The Mantus also uses a little buoyancy in the Rollbar. Most other Rollbar anchors have the galvanising breathing holes at the top, where they will let any air out. The Mantus has two holes quite low down on the Rollbar so it retains some air. Like the Spade the volume is small so it is difficult to know if it has any practical effect, but I am surprised the feature has not been copied by others.

I wonder if it worth plugging the breathing hole in the top of the Rollbar for anchors like the Rocna. There will be no pressure build up because the bottom is open. However, I am reluctant to recommend modifications to anchors without some testing. The effect would only be slight, but I think possitive.

[pcmm]

Originally Posted by TheThunderbird

@ pcmm
My point is about a shorter shank, not a weaker one.

On CQR, and other anchors design, the section is designed for stronger resistance on vertical bending (eg retrieval) and less on lateral (CQR being almost zero-stressed, as it's pivoted)

Yet, i appreciate that a shank may keep working on the anchor, now and later, to a benefit :-)

YTes. A Shorter shank only works if thats part of the design for the angle of fluke penetration. shortening the shank tends (in most cases) to increase the angle at which the shank penetrates the sea floor. This works up to a point. The Fortress anchors use this to their advantage with steeper fluke angles for mud vs. sand.

Almost all anchor shanks are designed to be strongest in the vertical plane as that will be stressed every time the anchor is retrieved. Aside from the CQR almost no modern anchors have a hinge for lateral swinging. But its not for the reasons you think. The CQR ( of the anchors available today) is the most likely to land on the sea floor on its side! the hing allows the plow to pivot DOWN into the sea floor. Check out SV panope's youtube series on anchor tests. I believe he's up to 65 videos showing anchors hitting the sea floor and setting. At this point I would suggest he is THE expert on anchor tech! no one has done as much anchor testing with as much consistency as he has. Not he's also tested Bruce copies ( that have different geometry than the original Bruce's and the results are suprising!

[a64pilot]

If you think buoyancy in the shank is an asset, its easy to test, just zip tie a float to the shank and see.

[LakeSuperior]

Originally Posted by noelex 77

If the Ultra shank is sealed it will certainly be enough to produce a noticeable effect. It would be nice to confirm if it is truely sealed. The original Ultra had no bracing webs in the shank and it is hard to imagine the stainless walls are strong enough to withstand the pressure at depth. Even at 10m the pressure is around 30Psi. If the anchor dragged into deep water it could be at the full depth of the chain. At 100m the pressure is around 160 psi. To put this into perspective the welds of stainless fuel/water tanks are normally tested at around 3-7 psi. Tank walls have a much bigger surface area (critical to the total force), but it still would be nice to get some confirmation from Ultra about the sealed shank.



So I think the retained trapped air volume in the Spade shank will be small, but every little bit getting the balance of the anchor correct is a help and think it probably has a slight, but useful effect.

The Mantus also uses a little buoyancy in the Rollbar. Most other Rollbar anchors have the galvanising breathing holes at the top, where they will let any air out. The Mantus has two holes quite low down on the Rollbar so it retains some air. Like the Spade the volume is small so it is difficult to know if it has any practical effect, but I am surprised the feature has not been copied by others.

At 10 m the pressure differential would be approximately 14.7 psi. In order for it to be 30 psi the manufacturer would have to draw a vacuum.
Looking at the anchor shank cross-section a pressure differential at any practical anchoring depth is not worth considering.

The hollow shank has the effect of making the shaft lighter. That is, there is a reduced amount of steel in the cross-section. This is exactly the case if the void is not sealed to seawater.

If the void is sealed there is a buoyancy force making the shank appear to be minimally lighter. In essence, you have a slightly lighter weight shank when compared to the flooded void and it has the mechanical properties of the steel box.

I speculate that a longer shank important to obtain a longer lever arm which makes it easier to torque the anchor out when imbedded in mud, clay, or larger cobble. It would also force the tip down for purchase.

[noelex 77]

Originally Posted by LakeSuperior

At 10 m the pressure differential would be approximately 14.7 psi. In order for it to be 30 psi the manufacturer would have to draw a vacuum.

Sorry you are right the pressure the Ultra shank walls have to withstand if sealed is about 15 psi at 10m and 146 psi at 100m.

[Spade Anchor]

Please do not drill holes in the shanks of the Spade Anchor it is the only thing that voids the lifetime warranty.

[noelex 77]

Originally Posted by Spade Anchor

Please do not drill holes in the shanks of the Spade Anchor it is the only thing that voids the lifetime warranty.

. Holes in the shank are not a good idea in any anchor.

[a64pilot]

Originally Posted by noelex 77

. Holes in the shank are not a good idea in any anchor.

But if I drilled enough of them it would decrease the weight and shift the CG of the anchor

[noelex 77]

Originally Posted by LakeSuperior

If the void is sealed there is a buoyancy force making the shank appear to be minimally lighter. In essence, you have a slightly lighter weight shank when compared to the flooded void and it has the mechanical properties of the steel box.

Here is a photo that gives some idea of the volume of the Ultra shank. Ultra owners think nothing of buying two. One $7000 dollar anchor is not enough .

The convex shape gives the shank some volume. If it is sealed, the reduction in shank weight when deployed is simply the weight of seawater that the interior of the shank would hold if it was not sealed. While not great I think this would be enough to have a practical effect.

Would anyone like to hazard a guess at the reduction in shank weight from the buoyancy?

[Kenomac]

Originally Posted by noelex 77

Here is a photo that gives some idea of the volume of the Ultra shank. Ultra owners think nothing of buying two. One $7000 dollar anchor is not enough .

The convex shape gives the shank some volume. If it is sealed, the reduction in shank weight when deployed is simply the weight of seawater that the interior of the shank would hold if it was not sealed. While not great I think this would be enough to have a practical effect.

Would anyone like to hazard a guess at the reduction in shank weight from the buoyancy?

It's definitely a sealed shank.