Which size anchor

[Brian@Fortress]

I have a cat - 40 ft, 5 tonnes. I have anchored all round the Atlantic circuit and learned a few lessons. My complement is a 16 kg Delta for Bower, an FX-16 as a kedge and an FX-37 for when nothing else can save me.

Over a year's cruising there were two occasions when I dragged with the Delta. One was in heavy kelp in the Spanish rias where the only remedy was to re-anchor and probably nothing but a massive Fisherman would have held. The other occasion was in a hurricane hole in Antigua where the bottom was pretty much liquid mud. The Delta did nothing but the FX-16 (on the soft mud setting) headed towards the centre of the earth. The problem was that after 3 days it wouldn't come back up as it had dug in so deep. In the end it came up after 1/2 hour heaving short and motoring around. I am certain that if I had used the big fortress I'd have had to abandon it.

Snowleopard, it appears that you encountered a similar bottom type to where the Chesapeake Bay test was conducted, as per the images below:

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Here's the 21 lb (10 kg) FX-37 once we got it back aboard after one pull test:

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And after we hosed off the soft mud:

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We ended up losing this anchor during one attempt to retrieve it when we were directly above the anchor and pulling hard at a 1:1 scope. The winch operator had calculated that the anchor was buried 13 feet (4m) into the mud, and the 5/16" wire rope broke at 3,500 lbs (1,588 kg).

After a total of 60 pull tests with the FX-37, Danforth 35 HT, and the 44-46 lb (20-21 kg) new & old generation steel anchors, we decided to deploy the 10 lb (4.5 kg) FX-16 that we had brought aboard at the 45° angle for soft mud, and it was definitely one of the most difficult anchors to retrieve during the entire testing:

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Here's a video from one of the FX-16 pull tests, at about 8:00 minutes:
https://www.youtube.com/watch?v=4Ga1_LCZ90g&spfreload=10

 

[sailorman]

Just like anchoring in The Pyefleet

 

[J Neeves]

Jonathan: just to clarify: by 'thick' and thin' I presume you're referring to the consistency of the mud rather than it's depth? If I remember correctly, the Chesapeake test referred to 'soft' mud (or what one might call mousse, judging by the results ).
(Great language, english: more words than any other and most of 'em have at least two different meanings.)

I stand corrected - I was not clear, I meant thin as in watery, mousse like (I might start to use that ) - not thin as in a few inches, or cm.

The Chesapeake I assume is variable like every other seabed but in the areas chosen for the tests some of the mud looked like engine sump oil (or blackcurrant mousse) (you could see it over the hands of the lucky operator who retrieved the anchors by hand) but at depth is tended to have much less water. I do not know but assume that the key to success and developing hold was penetrating the mousse like top layer. The Fortress, set to 45 degrees, was the standout success (which is one guesses, why the tests were conducted) but the appalling performance of some of the other designs was a real eye-opener. Another guess - I might project (another word with multiple meanings), or extrapolate, that a Fortress will still outperform most other anchors in soft sands, but to a less marked degree, and at some point of sand hardness (i.e. getting harder) performances of NG and Fortress are more similar.

We all have our favourite NG anchors but I suspect that blindfold no-one can tell the difference in most sand seabeds. Consequently testing in sand is of not too much value now - what we need to know are the limits set by different seabeds of each design and very little testing is done in seabeds other than sand.

Jonathan

 

[J Neeves]

Thanks for all the replies and tips, i think the 16kg Delta will be best suiting for the moment

When the thread opened I had assumed the OP had decIded on a Fortress and simply needed advise on size. As common with anchor threads we had some drift suggesting different designs and not answering the question that I thought had been raised. I would tend to go with macd and Snowleopard, a Kobra rather than a Delta and more than one anchor to cater for different seabeds (and we would not sail without a Fortress). Each anchor carried should be capable of being the main anchor, anchors are lost - which is one reason there are so many anchor makers!

I would not discard alloy, even as a main anchor. They do tend to be expensive, alloy Spade or alloy Excel - but they allow one to carry a lightweight NG as a spare without too much weight penalty.

We like Snowleopord find that a 15kg steel anchor is commonly adequate for most conditions, Snowleopard is slightly bigger (more windage) than our cat but we carry back ups, in case we lose one, someone else loses one or conditions are questionable.

I hate to suggest further reading (and dislike self aggrandisement) to the OP but I hope my views are expressed neatly in the April, 2015, edition of Sailing Today.

Jonathan

 

[noelex]

Anchors like the Delta and Kobra are good general purpose anchors. They are excellent value for money, especially the Kobra, but if the budget can stretch a bit further one of the good new generation anchors like the Manson Supreme, Mantus, Rocna or the steel Spade, will give better performance again.

These two photos of a Delta and Mantus will give you an idea why it is worth spending more money. The first two photos show a Delta. You can see the long setting distance, which has reversed around as the wind changed direction overnight. The Delta has not been able to penetrate the harder sand layer and is holding the boat mainly by piling up sand in front of the fluke. Contrast this with the Mantus that dived down within a shank length.

Both anchors held the boats overnight and the Delta owner was unaware that the hold was marginal.



Delta:

Delta:

Mantus:

 

[J Neeves]

Can you confirm that the seabeds, the power of the engine used and time to set and the care with which these anchors were set is identical? If there is any difference in any of these conditions (and any of the other variables, for example scope, or amount of weed) then these images do not compare like with like and are dangerously misleading.

edit Equally - maybe the images show the simple effectiveness of the Delta, - it worked even though apparently poorly set? close edit.

Jonathan

 

[snowleopard]

Snowleopard, it appears that you encountered a similar bottom type to where the Chesapeake Bay test was conducted,

For reference - English Harbour Antigua, the inner harbour.

 

[J Neeves]

Snowleopard,

I note you used a 16kg Delta with success and I wondered at your dimensions (if I can be personal) as we also use a 15kg bower (though are quite happy with a 9kg alloy Spade (A80). I note you are 40' LOA and weigh in at a miserly 5t (how do you keep the weight so low?!). I note you mention 18' between engines (on the 'Multihull' thread) or is this overall beam? We are 38' with a 22'6"beam but in cruising mode (water and fuel) would weight in at around 7t (we have 2 MD2020s). I also note you use of the FX 16, with success - and had wondered if our FX 23 was 'too' big ) though its area is not much bigger than our bower or our Spades (we have s feel one as well). We have no complaint of the FX 23 but wondered if you had ever found, or thought, the FX 16 too small.

We seem to have arrived at a surprisingly similar portfolio of anchors.

Jonathan

 

[snowleopard]

Snowleopard,

I note you used a 16kg Delta with success and I wondered at your dimensions (if I can be personal) as we also use a 15kg bower (though are quite happy with a 9kg alloy Spade (A80). I note you are 40' LOA and weigh in at a miserly 5t (how do you keep the weight so low?!). I note you mention 18' between engines (on the 'Multihull' thread) or is this overall beam? We are 38' with a 22'6"beam but in cruising mode (water and fuel) would weight in at around 7t (we have 2 MD2020s). I also note you use of the FX 16, with success - and had wondered if our FX 23 was 'too' big ) though its area is not much bigger than our bower or our Spades (we have s feel one as well). We have no complaint of the FX 23 but wondered if you had ever found, or thought, the FX 16 too small.

We seem to have arrived at a surprisingly similar portfolio of anchors.

Jonathan

To try and take your questions in order -

The overall dimensions are 40' x 23' - the 17' figure I quoted elsewhere was distance between hull centrelines/props.

The weight is so low because I built it in foam sandwich composite rather than the solid glass used in most production cruising cats. When loaded up for ocean crossings we were down on our marks to around 6 tonnes.

My FX16 is strictly for use as a kedge though we used it in lieu of the bower in the sheltered hurricane holes. I would have gone up to the next size if I'd planned to use it all the time. With an electric windlass for the bower we never use the kedge as a lunch hook, only for the soft mud scenario or when we need to put a second anchor out.

The Fortress size table - http://fortressanchors.com/selection-guide/fortress indicates that the FX23 would be the correct size for a bower on our boat. I don't consider that I need to go a size bigger than a corresponding monohull as (a) I'm much lighter and (b) with an unstayed aerofoil mast my windage is probably quite a bit less.

 

[Birdseye]

Were looking into replacing the anchor and chain on our catamaran which is a Prout 33CS. Its looking like a Fortress and 10mts of 8mm chain + rope is whats required, the question is though should i go for the FX11 which is suitable for 8 - 10 mts or the FX16 which is suitable for 10 to 12 mts

The quest is a light boat and is 32ft or 9.5m long. When we had one, our spare anchor was an aluminium bulldog of a size slightly smaller than the fortress FX11 and it worked fine.

 

[Brian@Fortress]

For reference - English Harbour Antigua, the inner harbour.

Interesting, because I thought the Caribbean was almost exclusively sand or sand/clay, with occasional rock and coral. However, Bob Taylor, a retired US Navy soil mechanics and anchor design expert who consulted for us on the Chesapeake Bay anchor test, mentioned that soft mud can be found in many bays, harbors, lakes, rivers, and seas throughout the world.

J Neeves mentioned the "appalling performance of some of the other designs" in a prior message regarding this anchor test, which was astounding to many of us who were aboard the 81-ft Rachel Carson research vessel, but this poor performance came as no surprise to Bob, who stated that "anchors which are designed and optimized for harder soils will typically only have a a holding ratio of 10-15x (holding capacity divided by anchor weight) when used in a soft soil."

This is almost exactly what we found in the Chesapeake Bay, as the 44-46 lb (20-21 kg) new & old generation plow or shovel type of anchors usually achieved holding capacities of 450-700 lbs (200-320 kg) in the soft mud, which is worth noting from a safety aspect if you are depending on one of those anchor types in that soil and you might possibly encounter high wind conditions.

 

[snowleopard]

Interesting, because I thought the Caribbean was almost exclusively sand or sand/clay, with occasional rock and coral. However, Bob Taylor, a retired US Navy soil mechanics and anchor design expert who consulted for us on the Chesapeake Bay anchor test, mentioned that soft mud can be found in many bays, harbors, lakes, rivers, and seas throughout the world.

In these enclosed harbours where there is no creek running in and effectively no tide, ooze sinks to the bottom and is never flushed out. The outer anchorage at English Harbour is sand but inside the narrows the bottom is very soft mud. Indian Creek nearby is even worse - liquid mud.

 

[Birdseye]

I did some work on comparing windage of our cat with a monohull. I had access to Bav 35 and Bav 45 drawings of around a 2010 vintage and calculated that the cross section area, above waterline, of both beam and length of our cat and the Bav 45 were similar (and the Bav 35 was 30% less). I excluded mast, furled sails etc - so very simplistic - but it gives you an order of magnitude. Obviously underwater profiles differ and we weigh in at 6t, unladen vs (I recall) 11t for the Bav 45. Very crudely the windage of a cat is about the same as a mono that is 30% longer

n

Before I bought our cat I had several long chats with the guys at southampton University who did the multihull capsize work for the EU when the RCD was being drawn up. Like you I had done some work on the above water profile, wind resistance and righting moments etc but was surprised to be told that in tank testing the university had found that the aerodynamics of the between hulls underneath part ( ie the bit between the hulls facing the sea) was very significant. Well you dont get lift without drag so my guess is that the drag from a cat will be significantly affected by this bit.

 

[J Neeves]

Snowleopard,

Thank you for the reply.

Earlier I quoted a comparison of windage between a monohull and a catamaran. The idea was to make the comparison and allow an owner to then make their own judgement.

Anchor sizing tables appear not to have changed since the days when only a CQR, Bruce or Delta were available despite their being newer and better anchors that might allow those tables to be modified. However I do note that the Classification Societies (CS) do allow use of a smaller anchor if it meets SHHP requirement, and many of the NG anchors would certainly meet this for their holding capacity (and some are tested and certificated as such) though some might be most questionable for strength. I appreciate CS testing is hardly perfect but it is conducted under controlled conditions and I am unaware of any vessels that have used a CS certificated anchor being lost as a result of anchor failure - some might say the CS recommendation has stood the test of time. 'Magazine' tests (and the recent Fortress testing) is effectively CS holding power testing with the results made available to the public (where all anchors are tested the same way in the same seabed etc).

Contrarily most people when they buy a NG anchor go up in size (though the logic defeats me - it appears to fly in the face of the performance improvements that motivates them to choose the NG anchor in the first place). But I cannot criticise anyone who altruistically wishes to improve the pension funds of anchor makers. Another factor that has changed the equation is that many of us now use snubbers (and on a multi a bridle) and we use these devices to absorb the energy of the veering or hobby horsing yacht - correct use of a correctly sized snubber will factorially reduce the load on the anchor.

Given your and my windage, being that of a 45' yacht, we both independent of each other have bought and used with success an anchor (or anchors) that might be considered small. However maybe the high wndage, but low weight, in some combination (Vyv raised the idea maybe we, a multi, sat at anchor 'better' than a mono?) allows our anchors to set 'better' by themselves than on a monohull. I also underline we carry 'spares' all of which could be used as the main or bower anchor and when a F8-F10 is forecast and we are unable to escape the wind then we would deploy 2 anchors in a 'V' and if this is necessary and can be completed by dinghy we would not hesitate to use an alloy anchor as they are easier and safer to deploy.

But to return to size, which is what the thread was about - it would be interesting to learn of any yachts with our windage, that 45' mono, who might also use an anchor smaller than that defined by the anchor charts who were motivated by the Classification Society allowance of that smaller anchor if it meets SHHP, or is a good example of NG. Even better would be to learn of anyone who uses a Knox anchor whose manufacturers suggest their model is even better than most NGs.

Jonathan

edit - Birdseye - our posts crossed. My idea that windage of a cat is 'equivalent' to a mono 30% longer is crude in the extreme - there are so many other factors (and you mention one I had not thought of) close edit