Photos of Anchors Setting

[noelex 77]

The Bruce was nearby and experienced the same wind shift and thunderstorm. They did not drag. Unfortunately they left early the next morning before I could look at their anchor.

[noelex 77]

We backtracked a little and ended up at the same anchorage as in Post #1103.
A beautiful spot, but not a great substrate with some rock underneath the sand. As you can see the set is almost a carbon copy of Post #1103.

[noelex 77]

This looks like chain on the bottom. In fact it is the indentation made by our chain last time we were at this anchorage. In hard sand these indentations remain a long time and can look remarkably like real chain. The reason I mention this is that it is easy to follow these marks believing you are following your chain. I have even made this mistake when diving and looking from the surface, but it is particuarly easy to make this error if using a bathyscope.

One danger is that you can falsely conclude your anchor is completely buried when you come to the end of the "chain" and nothing is visible.

This is one reason why I like a short float on the anchor. If you cannot see the float you know you have not found the anchor. Without one it is easy to be misled by marks like this. In softer sand you can also get the problem that chain may sink below the surface. This can happen some distance from the anchor and once again it easy to falsely conclude that the anchor is completely buried.

[noelex 77]

This is the same anchorage as post #1121. At this time of year the wind flips rapidly in direction so we have moved back and forth to gain the relevant protection.

The Mantus has produced an almost identical set. They are so close that they could be near identical photos. These sort of results do give me confidence that the performance is quite reproducible in the same substrate.

[noelex 77]

We sailed back to the same anchorage as post #1142 for some protection from the wind flipping to the NW again.

The set is so close to identical I had to double check I had not mixed the photos up

[Prairie Chicken]

Consistent results are a desirable quality!

[Jim Cate]

Originally Posted by Prairie Chicken

Consistent results are a desirable quality!

Consistent GOOD results are a desirable quality!!

Jim

[noelex 77]

There is lovely reasonably soft, uniform sand as far as the eye can see at this anchorage.

It is the same anchorage where the Octopus made its home under my Rocna about 15 months ago. I borrowed an underwater camera from a friend to take the photos, which prompted my interest in underwater photography.

You can see the Mantus has set deeply and quickly. There is tiny bit of heaping up, but this is really nit picking.

I will hunt up the photos of the Rocna at the same anchorage and post them later as a comparison.

[noelex 77]

These three photos of my Rocna was taken fifteen months ago in almost the identical spot. The anchorage is in a large bay with a vast expanse of what looks like uniform substrate (apart from a crashed plane's nose cone). Same sized anchor, same chain, same setting technique.

However, the photos of the Rocna was taken after the Octopus has spent several days digging sand out from under the fluke and also sitting on top of the fluke and scouring a big hole. So you need to use your imagination to fill in the sand level. It is easier for me because I saw the Rocna before the Octopus decided it would make a nice home .

Even if you make some allowance for the Octopus, overall the Rocna has not set quite as deeply as the Mantus. This is only one example, but I have been using the Rocna for the previous 5 years so I have seen the Mantus in the same anchorages as the Rocna on several occasions.

The two anchors are very close. They work and set in a very similar way, as you would expect from their overall geometry. However, this single anchorage mirrors what I have found generally with the Mantus setting just a little deeper, a little more rapidly and a little more level than the Rocna.

I will try to outline the differences in a more detailed way on a separate thread in the near future.

[colemj]

Do you think the kicked-up back part of the Rocna fluke keeps it from digging as deep as the Mantus?

How far down an anchor digs may not be a good indicator of holding power. An anchor only needs to dig until it can resist the pull applied to it. If it doesn't drag, it is well-set regardless of its depth or angle, etc.

We have anchored many times in harder substrate (hard packed sand or clay) where only half the fluke was dug in regardless of how much backing power was applied. After taking high wind days, the anchor hasn't moved or dug in further.

Mark

[NornaBiron]

This is our 45 kg spade, a 25 kg CQR, a 25 kg Manson supreme and a 20 kg delta, all set within 300 m of each other

[colemj]

The CQR cracks me up - I don't think I've ever seen one not lying on its side.

Mark

[noelex 77]

Originally Posted by colemj

Do you think the kicked-up back part of the Rocna fluke keeps it from digging as deep as the Mantus?

How far down an anchor digs may not be a good indicator of holding power. An anchor only needs to dig until it can resist the pull applied to it. If it doesn't drag, it is well-set regardless of its depth or angle, etc.

We have anchored many times in harder substrate (hard packed sand or clay) where only half the fluke was dug in regardless of how much backing power was applied. After taking high wind days, the anchor hasn't moved or dug in further.

Mark

That is true, but when I apply my setting force with the motor the anchor is still slightly digging in at the end of of my 30 seconds full power.
See this video:

Mantus Anchor setting - YouTube

I think the Mantus digs in just a bit quicker than the Rocna. I would stress I am talking about small differences. It is only using the two anchors back to back over a long period of time and observing the anchor rather obsessively that these minor differences become apparent. I also think the differences in this aspect of performance may not be very important. If an anchor sets in 3 feet or six inches less than 3 feet, is not very significant especially when other anchor designs take many metres to achieve the same thing.

The upsweep at the back of the fluke of the Rocna is interesting. This has not been adopted by the Manson Supreme and Mantus, nor was it present on the grandfather of the roll bar anchors, the Bugel. I suspect the upswept back of the fluke is a slight help with those anchorages where there is a thin layer of sand over rock substrate. In these sort of conditions the anchor is dependent on holding and accumulating as much sand on the top fluke as possible, which is aided by the upswept trailing edge of the fluke. On the other hand it does provide a slight impediment to anchor diving.

I think the upswept trailing edge of the Rocna blade probably plays only a minor role in the differences between the two anchors. The biggest difference is the "wings" and wider roll bar of the Mantus. This presents the tip at more aggressive angle to the substrate when initially setting. The drawback is that it makes the Mantus a wider anchor.

[noelex 77]

We had some nice steady winds at this anchorage. High twenties for a few days.

I thought I would show what happens to the anchor under these conditions.

Really nothing much happens at all

The Rocna would not start to dig any deeper until the wind hit 25-30 knots. As you would expect the Mantus is very much the same, although perhaps the windspeed is a few knots higher. This may be because it sets just a little quicker and deeper when the reverse is applied, but if there is any difference it is only a few knots.

If you do have the chance to dive and look at look at your anchor it is worth knowing the windspeed when the anchor should dig in further. The usual cause of the anchor not burying further with stronger wind is the anchor encountering rock, so the anchor not digging down further when it should is a clue that there is a problem with the substrate.

The anchor will move back slightly as it buries. Here there are big differences between different models. With good anchors this movement will typically be very slight, usually inches. With other models it can be many metres.

The windspeed that the anchor should bury further is mostly dependent on the amount of setting force you apply. The higher the setting force used, the higher the windspeed before you see any change. Surprisingly, anchor size does not make much difference. A smaller anchor will set deeper with the setting force, but the wind has to produce more force than achieved when setting before there is any further change.

The first couple of pictures are Mermaid shots. At first glance the shank looks a little more exposed, (compare these to post #1148) but this is caused by the shank moving back and forth scraping the sand away. If you look closely the fluke is just a fraction more buried:






The next photo is a surface shot a couple of days later. The anchor is once again perhaps a touch more buried. Th e difference is very marginal.

[noelex 77]

The substrate here is mud. 7m @4:1

All anchors tend bury well in this sort of substrate. Typically even a Delta will disappear quite well, but the smaller convex shaped blade does not offer a lot of resistance.

This is a photo from the surface, but you can see the Mantus has buried very deeply. Without the roll bar there is nothing to show where the anchor is located. As usual the anchor has set within a couple of feet. There is almost no heaping up.

It is worth remembering that while the set looks very deep this sort of substrate is only soft. Clever anchor geometry that can penetrate hard surfaces becomes less important. A large blade area is important in producing adequate holding power unless the substrate becomes much firmer with depth.