Anchor Loads - Which size of swivel?

[Neeves]

Noelex,

After you bent the shank of your Mantus, which you illustrated in post #338 (in your thread on pictures of anchors), you had a replacement shank nicely illustrated on post # 1875. I note that on a recent post, #1917 your anchor now has a spiffy new label on the shank. Is this a new anchor, or just a new label?

My memory is not that great and it was along time ago but I also recall you mentioned, I might have this wrong, that when you bent your shank - the anchor continued to hold. Which seems to be counter to your words of warning above.

Really excellent images, I wish the water was that clear in Australia.

Jonathan

I would have sent you a PM on the label issue but you cannot, or do not, receive PMs.

 

[vyv_cox]

One aspect in considering the ideal anchor connection solution that is rarely mentioned, is the risk of the attachment jamming and producing an unfair lead.

Even a simple shackle can sometimes jam and lock in the slot in the anchor shank in such a way that the chain is leading from the anchor in an unfair way.

So if the shackle can get jammed in the slot in the anchor shank, the chain and therefore the force on the anchor may be from one side of the shank, or be higher or lower than normal.

The shackle will be less strong if it becomes jammed like this, but of far greater significance is the anchor performance may be significantly be affected by this off-centre pull, to the anchor may only set very poorly.

No matter what connection you have between the chain and the shackle, it is worth trying to pull it from different directions to see if there is any risk of the connection jamming in place.

In fact I have discussed it quite a lot, although not in this thread, and there are several examples of it on my website. I also had an article in YM on it a few years ago. It was the reason I developed my three links technique. I found when testing the Osculati cranked swivel that it was impossible to prevent the shackle from wedging itself between swivel and anchor, resulting in several failed anchoring attempts due to dragging with the Osculati facing straight down. A poster on the CA forum reported the same problem. Adding links of chain seemed to be defeating the object of the cranked swivel, which now languishes unloved and unwanted in my bilge.

 

[noelex]

Is this a new anchor, or just a new label?

No new anchor, or even a new label.

Your memory is correct. It was very surprising to me that an anchor even with a bent shank continued to perform well. The Mantus has very good roll stability. I suspect that a reduction in roll stability is the first casualty of any horizontal displacement of the point of attachment, so these results may not be generally applicable to other anchors, but it was interesting nonetheless.

BTW The shank bent trying to get the anchor up after it buried deeply following a couple of days of 45 knots, but it was also the original mild steel version. The shanks have all been updated to ATSM514, which is the same strength as Bisalloy 80 used in Manson Supreme and original New Zealand Rocna. Manson boast there has never been a bent shank on a Manson Supreme (although I have seen a bent fluke). The Mantus shank is a not as deep and not as indestructible as the Manson version, but the reduced weight improves the anchors performance. The Mantus warranty covers bending and there is no need to return anything. unlike many anchors and no need to return anything) Mantus even offered to upgrade all the existing shanks to ATSM 514 at no charge. Some other anchor manufacturers could learn from this example.

Really excellent images, I wish the water was that clein Australia.

Thanks. The water clarity in the Med together with the hard sand make it an ideal enviroment for studying and photographing anchors. I studied anchors for long time in Australia and still like to do that when I get back. My favourite anchorages such as those on the Great Barrier Reef have much more interesting stuff to see underwater, but have only half the visibility that is typical here,

The other problem I find in Australia is that the lovely soft sand means even old school anchors work well and bury completely which makes it much tougher to pick any difference. I am not surprised that when looking at my photos you think all the skippers here don't know how to set their anchor.

 

[noelex]

In fact I have discussed it quite a lot, although not in this thread, and there are several examples of it on my website.

Keep spreading the word Viv. Your website is a great reference:
https://coxengineering.sharepoint.com/Pages/default.aspx

Anything that influences anchor performance should be our first priority. More boats get damaged by anchors dragging than anything else.

We seem to have a lot of gimmicks these days with "rock slots" and "anchor straighteners". If anchoring overnight consider not just the strength issue, which is discussed in great detail, but if these devices can effect the anchor's performance.

 

[Neeves]

Rock slots are not gimmick. If you fish they are invaluable and making an anchor for a yacht and an almost identical one with a slot for the fishing market will increase costs - and the last thing most of us want are increased costs. All slots can be locked off.

A quick look at marinas suggest about 50% of vessels carry swivels. To my mind most of them do not work (on retrieval there are still twists in the chain), are a weak link in the rode (many fail), are expensive and finally unnecessary (leave the anchor hanging just in the water and twists will unravel). However anchors do arrive at the bow roll back to front or upside down (so half twist left) and anchor righters, Boomerangs, Bananas etc can be stronger than the chain (here they are made from Bis 90), have no moving parts and with the help of Newton right the anchor. If you have a heavy anchor the self righting device is cheaper than visits to a chiropractor to sort your back.

Maybe if you were a fisherman, had to apy extra for a small run lot of an anchor and had tried the self righting device you would have a different view

Jonathan

Edit You say in your post No 524 on your thread on CF that your Mantus set, even with a bent shank (this was the time you got the trolling line round the prop) - so though the anchor bent on retrieval, previously, you seem to suggest you continued to use it, bent shank and all, suggesting that a misaligned shackle would not be the great problem you suggest.

My understanding is that roll stability had nothing to do with the alignment of pull it was all about anchor design. It does not become apparent unless the anchor is moving, dragging, so as long as an anchor sets firmly whether it is roll stable or not is irrelevant. Obviously if an anchor drags, maybe because its is in a very soft substrate, then roll stability would become an issue (as Fortress possibly demonstrated). However there is no indication that any modern anchor is not roll stable. Unstable anchors appeared to be only pre-modern models. As the Ultimate Holding Capacity of modern anchors is so high - it would be an unusual seabed if you could get one to drag any distance other than setting more deeply.

I have never seen any work, apart from the evidence you provide, of an anchor being observed with a misaligned load. The bend on your Mantus shank is quite severe - much greater than would be imposed by a misaligned shackle. close edit

 

[vyv_cox]

Not sure about fishermen and rock slots, every fisherman I see in Greece, which means countless thousands as every tiny port contains a dozen or more boats, carries grapnel anchors made from rebar. All the chandleries sell them, very cheap. Combined with polypropylene warp it is no great loss to cut them free if they become irretrievably jammed in rock, although I don't suppose that is a very common occurrence.

 

[RichardS]

Not sure about fishermen and rock slots, every fisherman I see in Greece, which means countless thousands as every tiny port contains a dozen or more boats, carries grapnel anchors made from rebar.

Same in Croatia. They look really ugly and rusty but I guess they must work?

Richard

 

[Neeves]

We only have Australian fishermen here and they generally fish for leisure, not work. They would certainly not use anything like knocked up rebar grapnels as they would not be accepted (as anchors) and would make the nice white runabouts look pretty grotty. When any Greeks or Croatians come past (they should be easy to recognise if they are all ugly and rusty) I'll check what they use.

Jonathan

 

[Neeves]

If you are ever unlucky enough to have your aircraft fall into the sea around Auckland the rescue boats have anchors with rock slots. Or if you are in the unlikely event of being caught speeding in your yacht round Auckland, the police have slots in their anchors. Many of the work boats for the oil industry, these tend to be monsters, say 100', in either Bass Strait or the NW Shelf - they too have rock slots in their anchors. And then at the smaller end of the scale anchors with rock slots are fitted as standard on many runabouts. They meet a specific need and are bought and used as such.

Jonathan