Anchoring question, single of tandem anchoring

[Peter]

I’m looking to upgrade the anchors on the yacht (46ft, 13 te displacement), currently has 20kg CQR and a 15kg CQR copy. Which are generally OK for most situations. My question is do I buy a “oversize” anchor to cover a “storm situation” this would be around 30kg, big and heavy to move around. Or another 1 (or 2) 20kg Bruce or Delta anchors and using 2 anchors in tandem in a storm situation.. Does tandem anchoring give the same holding power a large storm size anchor

Thanks

Peter

 

[hylass]

Attaching two anchors to one rode, known as tandem anchoring, should be avoided. The double approach attaches a second anchor with around 15’ of chain in front of the first anchor. I personally almost lost my boat trying out this idea. At the time, my first anchor dragged. Needless to say, it was an old generation model, so I decided to try something new. I added a smaller anchor in front of the large one. This worsened the holding power as opposed to doubling it, drifting swiftly on the smaller anchor while the larger one couldn’t grip at all.

On an imaginary level, it might seem like two anchors should hold better than one. This is however only true when both anchors can set perfectly. Whatever anchoring technique you use, there’s never a guarantee that both anchors are going to set well. On the contrary, once the first anchor is set in the seafloor, it will hinder the other anchor from setting also.

For those who insist on using two anchors on one rode, I offer the following suggestions:

· Only use two identical anchors, with the same size and model.
· The size of each anchor should be able to withstand the load of your boat on its own, without the second one.
· The two anchors should be separated by a piece of chain of around 3 to 5 meters in length.
· Never attach the chain from the second anchor directly to the first anchor; instead, attach it to the connector of the first anchor.
· Finally, remember that new generation anchors have holding power far superior to older models, and they do not suddenly disengage from the seafloor like plate anchors. Instead, they slowly drift, remaining embedded. I am convinced that a single new generation anchor with high holding power is safer and more reliable than linking two old generation anchors in tandem.

 

[Salty John]

I agree with Hylas that tandem anchoring, in which a second anchor is added ahead of the main anchor on the same rode, is a device of the devil. I've tried it and it has nothing to commend it. I anchor to two anchors on separate rodes and your current anchor inventory is fine for this in anything but a major blow in less than ideal protection. The next biggest CQR, about 30kg, would give huge comfort but be a pain to handle. I'd be tempted to add another 20kg CQR. Two such anchors on all chain set 45 - 50 degrees apart will give peace of mind in pretty horrendous conditions. I've weathered some very nasty conditions on this arrangement on my 12 ton ketch. I like the CQR because of the forged construction and the swivelling shank which re-sets well at the turn of a tide. Lightweight, pointy anchors worry me a bit unless you use a heavy chain to keep the shank down and force them to bury.
Maybe you could then swap your lighter CQR-copy for a big Danforth which is great in mud. Then you would have a really good ground tackle inventory, assuming you also have the chain, chain stoppers, snubbers and windlass to go with the anchors!

 

[dom]

I came to cruising from racing and until a couple of years ago knew little of anchoring. After many worrying situations and a lot of messing around with different techniques I swapped to a Spade anchor which I believe the previous poster designed. It comes with a not inconsiderable number of claims and I was amazed to find that it really lives up to them! The anchor sets very quickly - like instantaneously - and so far that has been it with the boat staying put until the anchor is retrieved. It is a messy anchor to stow due to it's curved shank so I usually take it off after use which is a bit of a pain. However, for me this is more than compensated for by it's performance.

I should add I have nothing to do with Spade and have never met any of the guys.

 

[Guest]

I agree with the other posts more than 2 anchors on a single line endanger the boat if the wind shifts and they foul each other.

As for the size of the anchors they seem a tad light compared to ours and we are 35'. What you have missed is the weight of the chain. It is far more important than the anchors. Making sure the last 5m of chain is horizontal is the key. Our anchors have never dragged and we have rode out some extreme events with the bows dipping under the waves! Also having one of each type: CQR, Bruce and Fisherman's(huge) is the key for the different holding. CQR for sand, Bruce for mud and fisherman's for rock & weed.

 

[hylass]

[ QUOTE ]
What you have missed is the weight of the chain. It is far more important than the anchors. Making sure the last 5m of chain is horizontal is the key.

[/ QUOTE ]

Hi SolarNeil.. and sorry beforehand if I have to disagree with some of your comments..

The quoted sentence is an old belief.. but a WRONG one.
(For all mathematical explanation see "Tuning an anchor rode": http://alain.fraysse.free.fr/sail/rode/rode_b.htm)

It is important to have first some chain.. But I will say, mainly to avoid chaffing on the sea bottom.. then the "secret" is "SCOPE" and "Elasticity" In some places of the world, sailors are mostly using rope.. and they don't have more anchoring propblems..

(And many thanks for "Dom's" very positive comments.. /forums/images/graemlins/smile.gif)

 

[dk]

Peter
As with most of the other posters I would confirm that tandem anchoring is a no-no. Much better to go for more/heavier chain and an angel (an added weight which you slide down the chain to keep the pull as horizontal as possible. For a 43ft boat in Channel conditions I would go for two 20kg anchor of different types - ie add a Delta or Spade to your existing CQR - and 60m of 8mm/5/16th chain on the main bower. For Caribbean/World cruising I would go one step up on everything. Add 50m of anchorplait to the rode for riding out real stonkers. I've never really had problems, but I go for the 'it's no good in the locker' approach where I have the swinging room, and if the weather's looking dodgy I make sure I have the swinging room! Only in hurricane conditions would I consider a second anchor set on its own chain and rode, at 45deg to the first. Then I'd get off, go ashore and check my insurance policy!
D

 

[geem]

My experience in the Caribbean would suggest that the CQR is less than ideal in Caribbean sand. We used a 20kg Bruce on 30metres of 8mm chain as our main anchor. We are a 7 tonne catamaran. In addition we attached via a large mooring carbide hook, a 30 metre length of stretchy rode with 4 metres of 10mm chain and a very substantial aluminium anchor from a landing craft. It looks like a danforth thats been on steroids but can easily be loaded into the dingy and taken out at 45 degrees to the main anchor and set without getting a hernia. This worked very well and kept us safe when all were dragging around us.

 

[TLOM]

Peter

Seems like most posters are against the tandem technique. I haven't used it that often but on the few occasions I have I've felt very secure. Admitedly the wind wasn't forecast to shift - if it had I might have been reluctant to set the anchors that way. I sat through a steady F8 gusting F10 on a danforth + CQR in tandem + all chain in coarse mud. Both were well buried when we recovered them.

TLOM

 

[snowleopard]

The CQR is a popular anchor among British sailors and works fairly well in most circumstances. It is a very old design and some of the modern designs are considerably more effective in terms of holding power per kg of anchor weight. The Delta and Spade are well known examples; the Bugel is also gaining a reputation.

Your current 20 kg anchor is about right for the size of boat in normal conditions but I would suggest you carry a storm anchor for those nasty occasions. After a lot of research, I settled on a big Fortress for this purpose and I set it on a separate rode. My 9.5 kg anchor is recommended for 44-51 ft (my boat is a 39 ft cat, 5.5 tonnes).

My main anchor is a plough-type (Delta) and I find it drags in very soft mud. In these circumstances the Fortress holds very effectively using its special 'soft mud' setting. I won't use the Fortress if the wind/tide direction is likely to change as the shank can bend with an off-line pull.

Incidentally I also chose a 4.5 kg Fortress (rated for boats up to 38 ft) as a kedge. A side benefit of this one is that it is light enough to throw overarm, not something you'd want to try with an equivalent CQR.

Incidentally you may be aware that some CQR copies are dangerous. Incorrect geometry can drastically reduce holding power and the cheap far eastern copies made from cast iron snap easily.

 

[Guest]

I have read your site but try looking at the extremes. If the chain weighed the same as the water it would have no weight and any tug on the end would straighten it with little effort. If it weighed a massive amount, like a small ship anchor chain, then it would fall straight to the bottom as the horizontal pull exerted by a small yacht or pulling would be negligible. Unless there is a step function, then the middle ground has to be a progression. It is the weight of the chain that is the dampening force. Just like the age old invention of the angel.

The anchor has to be pulled horizontally to hold correctly. Otherwise if it held as well at other angles you would never pull it out of the mud.

So if the dampening force can cope with all that nature sends to it, (I am ignoring the trivial forces from simple wind on a yacht) and still leaves the last 5m on the ground you live to tell the tale! This is my practical belief and based on a 100% record not a spread sheet.

 

[hylass]

[ QUOTE ]
I have read your site..

It is the weight of the chain that is the dampening force. Just like the age old invention of the angel.

The anchor has to be pulled horizontally to hold correctly.

This is my practical belief and based on a 100% record not a spread sheet.

[/ QUOTE ]

Perfectly right SolarNeil.. except that:

1°) This is not MY site.. but the one of Alain FRAYSSE , an aérospace engineer, full time sailing his catamaran somewehere in the Pacific ocean..

2°) If you read carefully the mathematical explanation, you will understand that, if a chain has a catenary with light or moderate winds, and if an "angel" works well under the same conditions.. nobody care about the anchor holding in such conditions..

In strong wind conditions, when anchor holding would be more problematic, the chain is taugt and offer no more catenary, and the weight of an angel is too small to counter-act the static force of the wind and even more the dynamic forces.

3°) The anchor has to be pulled horizontally to hold correctly, and the pulling angle (again with strong wind conditions) is given by SCOPE

4°) Your practical belief, based on a 100% record.. is only a BELIEF.. a personal opinion, based on your personal observation only.. and you can believe what you want.. but this is not a scientific prove..

A very large quantity of poeple have also believed that the Hearth was a flat disc, and that the Sun was turning around it, during centuries.. and science has demonstrated that it was WRONG..

I'm conscient that it will take years before old beliefs, like thes ones, will disapear.. but I have plenty of time and nothing to win or to loose.. /forums/images/graemlins/smile.gif

 

[Guest]

Stay calm. I understand your point about the limit conditions especially with rope, but you say "offer no more catenary" That is a complete impossibility in the real world. Anything with a distributed weight will always have a droop! Yes, if you have rope that is close to buoyant and there is no stretch in the rope then you are just shock loading the anchor. You need to have a large scope to get the angle small enough for the anchor. The stretch in a rope is a good snubber.

But that is not how I anchor. I use the weight of the chain to be a huge distributed angel. The equivalent angel would be so big I would not be able to lift it as a single weight. I remember the tears getting the chain on board in the first place. Any shock loads just lift a proportion of the droop out of the chain. It is a different method. Neither is wrong: I struggle with a huge weight of chain and no powered windlass but my boat swings around a small circle. The other method uses lighter rope but needs much more scope. My second anchor is set up as rope so I know the difference.

A final point, when we hid behind a tiny reef in the middle of the Red Sea with the waves breaking everywhere I swam out to check the anchor. There was no movement of the anchor chain. I would never have survived with a rope in those coral conditions. Also, one of the yachts in the Pacific ended up against the reef as he used rope and chain. He was a racing nut (a nice one) that could not afford the weight of chain on board. Two methods and two outcomes, I will stick to my proven one.

 

[Salty John]

You experience and conclusions coincide with mine and your points are eloquently put. All chain, lots of scope and well proven anchors may identify me as a Ludite, but I've seen enough pointy, lightweight creations on bits of string let their owners down at the crucial time to stick with my flat-earth mentality!

 

[duncan]

surely you are arguing different things?

Lets get to the real bones of it - you have only one limit - 100kg weight, and we will consider any rope as 0, 8mm chain as 1.5kg/m or 10mm at 2.2kg/m.

you have only delta anchors to choose from in 10 - 60kg range

you can select an angel between the same ranges in addition
the water is 20m deep, no tide

what is the best overall package for holding?

 

[hylass]

well done Ducan,

May I suggest one more question:
- What about if the wind is steady at 50 knots with peak at 60 +??

 

[duncan]

I notice no responses...................

let me start then

60kg anchor

27m 8mm chain

rope to make up a full scope - here I would want 93m to give me 6:1 so 100m makes sense, another 50 would be fantastic.

this assumes 8mm chain is strong enough for the forces involved of course.

 

[duncan]

one more try .................and including the original post's question.

4 identical boats in the best shelter they can find - even ground at 20m depth no tide and plenty of room but

1 bad weather forecast

Boat 1 has a 60kg delta anchor, 27m 8mm chain and 93m warp

Boat 2 has 40kg delta anchor, 40m 8mm chain and 80m warp

Boat 3 has 20kg delta anchor 55m 8mm chain and 65m warp

Boat 4 has 2 x 20kg delta's set in tandem, 40m 8mm chain and 80m warp

Boat 5 has 20kg delta, 20 kg anchor angel (wherever - you choose) 40m 8mm chain 80m warp

Boat 6 has a 40 kg delta, 20kg angel, 27m 8mm chain and 93m warp.

As you can see everyone is playing with 6:1 scope and 100kg but in different ways -

Which boat will you be on?

 

[Guest]

Simple reason for no replies is that your arbitrary limits do not match my reality. So an additional "I would not sail on that boat" option is needed.

After studying in detail the referenced material it seems there is a misconception that the wind is the reason for anchor dragging. Three simple demonstratable events that disprove this are:
1. While close to a beach in the Mexican wind funnel I was able to motor at normal hull speeds into the wind to anchor. Wind speed above 30Knots.
2. While off Australia I was able to motor into winds that were higher than the B&G dial. >50Knots. Once the sea state rose it was only possible to maintain our position.
3. Without any sails and trying to go slow in 25knots of wind my yacht only travelled at 2knots. I find it impossible to go that slowly, on a no wind day, without taking the engine in and out of gear.

Therefore the windage on my yacht (with no sails) is less than the maximum force from the engine. Maybe my yacht is odd, but what it means is since I can not pull my chain up with just the engine then no wind can pull the chain up. So the wind does not matter.

I have always considered it the fault of either the owner, a fouled anchor, or water to cause dragging. The owner problem is easy to recognise. The fouled anchor is something like a iron bar caught in the Bruce anchor. "A brucy ball". etc etc. Or a bent shank on a sheet metal fabricated anchor after catching in coral. All real life incidents.

Water is easy. It is the waves hitting the boat. Which anyone that has done the Red Sea will know is the real reason for no forward progression. Close to the coast where the sea state is more confused and smaller it is easier to make progress in the same wind speed. The other proof of water being the real enemy is "The Tsunami". Also anchoring in an river that is above hull speed is nearly impossible.

There is one other reason, and that is the uncontrolled sailing of the anchor in high winds by high free board yachts. When this is combined with mainly rode anchors the snatch loads at the ends of the oscillations are huge. The anchor is trying to reverse the motion of the whole mass of the yacht. This is where the calculations differ between chain and rope. During the middle of the oscillation, with rope, the anchor is doing nothing. Whereas a chain is being lifting slowly off the bottom and reducing the top speed of the yacht at the ends of the oscillation. The anchor never sees the large shock loads.

Even with waves hitting a yacht they are not continuous. So with a rope the total energy is transferred to the anchor with just the rope stretch to spread the load over a longer time. With a chain the maximum force is not seen by the anchor until the boat has moved backwards and the chain has lifted to its highest point, all that time the chain pull is slowing the yacht. The anchor never sees the full force of the wave. A chain is basically a huge damping system to cope with intermittent high loads.

Since I have a nice yacht with low windage and I do not anchor in rivers above 6 knots my only enemy is the water. Since the water is an intermittent force I will always use a chain as a distributed dampening system.

Actually my real enemy is yachts with rode anchors. In a period of 2 days 3 different yachts, all using rode, directly in front of our yacht dragged their anchors. One poor sod dragged twice in those two days. All the yachts endangered my crew. Remember I was in the exact same conditions as them. So again without a spread sheet and using real world examples I have proved that it is the chain that is doing the work.

 

[duncan]

thank you for taking the time to pen such a full response.

I should probably start by highlighting that I was really getting at the comment in another post [ QUOTE ]
but I've seen enough pointy, lightweight creations on bits of string let their owners down at the crucial time to stick with my flat-earth mentality

[/ QUOTE ] for bringing together the issues of design, weight and string, when they are all topics in their own right.
You yourself bought the angel into the equation and, although you highlighted it's particular advantages with regard to enabling you to deploy a total weight in 2 parts that you would not be able to handle in 1 there are many that take the wrong message (that an anchor of x plus an angel of x will hold better than an anchor of 2x).
However, what you also introduced was the concept of having an anchor set up that can be handled as well as improved swinging , and I would add stowed etc - hence the alternatives I laid out for comparison.

We are in total agreement that snatch loads to the anchor itself are the 'enemy'. Where we would appear to disagree is that I believe that they cannot be avoided with an all chain rode within the normal restrictions on what is carried but can be mitigated by stretch in a nylon or polyester rode. You take the view that enough length and weight on a catenary will prevent the chain even going 'tight'.

I cannot match you personal experiences of extreme conditions, nor do I question the example you give. However I would question whether the boats using part rope rodes had the same overall weight in play - I have found a scary correlation between anchors and rodes in an informal survey I undertook. Almost invariably the boats with all rope had the lightest anchors, rope chain in the middle and all chain the heaviest/best anchors attached.

For a blue water cruiser there very little room for compromise on anchoring equipement but for the vast majority of boaters operating in relatively sheltered waters it is exactly that - a compromise. For Cats and most powerboats weight is the factor and the size of anchor is not the correct area for compromise.

Safe havens