Anchoring question, single of tandem anchoring

[Guest]

A few clarifications:

I only mentioned an angel in respect to the operation of the chain's weight. I actually disagree with the use of angels as it complicates matters when having to make a quick get away. I just meant the chain weight acts like an angel.

Also we are talking about safety, that includes the others in the anchorage. We make compromises on our boat but not about safety. The chain will not self stow because it is actually stored on top of the 3 tonnes of keel. It can be deployed fast but getting it stowed is slow.

Also we are talking about an addition 80Kg which could be between 1% and 3% of the boat weight. Why do they not fit high revving fully aluminium racing engines and high speed prop technology to save the weight on the engine. The simple answer is that everyone knows they can not stand real life. The same is true for the welded plate pointy anchors, and thin stretchy rope.

The problem is that a lot have people have been convinced by the long rode story, along with the story that the anchor does all the work. They seem to adopt it as a way to reduce weight. They then go out and anchor around all chain users and find they can not put out the scope they need. So they don't. So I end up with catamarans stuck on my bows in the middle of the night!

 

[duncan]

from me too -

whilst I don't have the experience of the conditions and variables you do I regularily anchor in 80m so carry a 220m working rode (with available extra if extreme circumstances) - all 8mm chain this would represent 330kg of chain to a 10kg anchor and 2500kg boat. You see the difference.

I am not a cat and have sympathy for you. Completely agree about responsibilities to others as well as your own craft.

That you for some reason bring engine technology into the equation I find bizzare but to put together [ QUOTE ]
The same is true for the welded plate pointy anchors, and thin stretchy rope.

[/ QUOTE ] is also confusing.

Are yo suggesting that the anchor manufacturers are in some way to blame for people using inappropropriate gear for their craft and the circumstances?

The last 3 cases of craft dragging thier anchors I saw was in fairly benign conditions in a sheltered anchorage (Newtown Creek IOW) on a tide change in the middle of the night. As far as I could tell all 3 were on an all chain rode - but that didn't make it the cause.

 

[webcraft]

Most anchors that drag have not been properly set.

If your anchor will take full astern under engine you are unlikely to drag in normal conditions unless the wind (or tide) shifts by more than 90 degrees and you are using a type of anchor that does not reset well.

If your anchor will not take full astern under engine then you should probably not all bail out to the pub.

- Nick

 

[duncan]

mines fine thanks................but I haven't tried the full power bit..........

having pulled a stranded speedboat off the beach (over a ton/inboard engine) with tickover in reverse last year I am happy with the anchor handling that!

more seriously I agree that for most displacement boats it's a good test. In some ground though some anchors will 'give a little' tested this way but not break out - mainly plough derivatives.

 

[craigsmith]

Disagree with this

[ QUOTE ]
Attaching two anchors to one rode, known as tandem anchoring, should be avoided.

[/ QUOTE ]For the record, we absolutely disagree with this and advise the exact opposite, when dual anchors are to be used to handle extreme conditions. For a variety of reasons. However I can't be be bothered getting into a fight about it, and feel that it is really a non-issue for most boaters, so those that are really interested can request our advice - or not.

[ QUOTE ]
· Only use two identical anchors, with the same size and model.

[/ QUOTE ]Agree

[ QUOTE ]
· The size of each anchor should be able to withstand the load of your boat on its own, without the second one.

[/ QUOTE ]Disagree, you shouldn't be using tandem anchors at all if one is enough. See below.

[ QUOTE ]
· The two anchors should be separated by a piece of chain of around 3 to 5 meters in length.

[/ QUOTE ]No, try a boat length.

[ QUOTE ]
· Never attach the chain from the second anchor directly to the first anchor; instead, attach it to the connector of the first anchor.

[/ QUOTE ]This depends on the anchor. Some anchors, including the Rocna, are designed to be used in a tandem set-up and have dedicated attachment points. Attaching the rode of the tandem to that of the primary is not ideal from the perspective of performance.

[ QUOTE ]
· 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.

[/ QUOTE ]Well that is definitely true.

<u>General advice</u> which I think Alain and I can both agree on: size your anchor adequately. Unless you're planning to visit the Antarctic or undertake other extreme trips, you are not likely to have a good reason to have to use dual anchors, in any set-up. When we advise on anchor size and associated equipment, we figure the single anchor should be able to handle, in good holding, winds of up to 50 or 60 knots. (Yes!). Only for scenarios above that do we start thinking about tandems.

 

[craigsmith]

[ QUOTE ]
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.

[/ QUOTE ]This is mostly correct SolarNeil but Alain's philosophy is partly true also.

The argument swings his way in shallow water, and your way in deeper water.

The argument swings his way for smaller boats, and your way for larger boats.

I will expand on those upon your request, if you cannot see why.

One other point: although the rode is critical, do not foresake the anchor entirely. If the boat is pulling on the rode with one tonne of force, then the anchor is pulling back with one tonne of force. If the scope and catenary is okay then hopefully it has little or no vertical component of force to contend with, but it still has to deal with that horizontal component of 1 tonne. If the anchor is too small or of an inferior design, it will quickly become the deciding factor.

Everything should be matched with appropriate focus on all components.

 

[GMac]

duncan, SolarNeil and Alain - I think I'm in love with you all. Any of you not married??

At last a anchor thread which recognises that a anchor is only 1 part of what must be a 'matched system' to work well. How many threads where this is not even mentioned. I must note that Alain does mention the bit behind the anchor often. You other 2 loverlies may have as well but seeing it all condensed like this is just a bit too much...

I voted no. 3 but I could not keep the Delta in my head and substituted a 'newer' type (just keeping anchor types themselves to the back of the chat a bit here). I was also thinking a 40ft average boat that does weekends away into sometimes semi-exposed areas, the odd race for fun and the odd extended trip i.e the Auckland to Suva Race (NZ to Fiji, 1000mls) and then has a 3-4 weeks cruise in the corel before coming back. This would be a typical use for most, especially down this way. A cruise to another country is a mimimum of 1000mls of very open ocean.

We believe (me and my team):

There is no substitute for - horsepower, elastisity, a real good woman, cold beer and chain.

For many reasons a length of chain is a must, the question is 'how long is that length?'.

The boats size and use has a big input to what and how long everything is.

The user (owner/skipper) of the boat is also an important factor.

The Feel Good factor must be there.

Our thoughts from down here. Based on a 40ft average weight/windage yacht.

Offshore cruising is the main use - All chain. MUST be accompanied by very good snubber/s. This is what we would use ourselves and 95% of the boats we supply gear to use. We have made some of the weirdest snubbers you could imagine but find 99% of these people use one or more. We prefer the simple bit of string with hook attached approch but 100% agree one is a must to have and use. From chatting most use all chain for a combination of chafe resistance and catenary weight. Anchor weight (sorry Alain but that is what most still use, at the moment) is mainly around 1.3 - 1.5 lb per foot.

Purely a FYI to the side - We see on the bows of cruising boats coming or leaving here: CQR (a fair few Manson versions but next to no nasty knock-offs), Deltas, Bruce ( approx. 20% being knock-offs). The Spade is becoming a lot more noticable and almost common. Being NZ we see a lot more Rocnas as well. The most anchor 'likely to be bent' CQR but Delta is close behind. We also get the odd Danforth and 'handymans dream'.
Generally the chain size leaving NZ is bigger than the chain size arriving. Boats arriving here and changing up a size is not uncommon, changing down is.

The boat used as discribed in my bit about the vote above - Most use somewhere between 20 to 40 mts of chain (most use 10mm but a few on 8 and 9mm) and 60mts of rope (most 16mm but some 20). Most down here run 80-100mt total rode lengths. The theory behind this is you can 'overnite' anchor on all chain and/or a smidgen of rope generally but have the ability to stay in deeper water if you like (using more rope) or stop for a fish in 80mts. Anchor weight around 1 lb per foot.

Harbour racers - 7mts of 8mm and 60mts of 12mm rope i.e mimium race requirements. The odd time these boats overnite they are rafted up to a 'mates' boat that carries real anchoring gear, the ladies (loose use of the word in most cases) and all the cold beers. 99% of the time the crews are that pissed they would not remember where they anchored when they woke up anyway and have been know to drag 100's of metres, the odd time rafted 4-5 up. Anchor weight - some have been seen to make plywood danforths painted grey but usually as lite as the rules will let them. An average kiwi racing weekend away

The type of boat will dictate whether the length of chain (and/or size) is bumped up or down a bit. Light and skinny could use a little less and heavy and/or big windage and/or big 'bowed' I'd go up. I'd agree wave action is more of an issue than windage generally.

The hardest obstacle we find is the owner. The Americas Cup brought a lot of new things to NZ including 'the cheque book boatie', the second most dangerous thing know to real boaties, the 1st being our wives . The guys could build you a computor in a dark cupboard in 60 seconds but drive a boat..... not. It is these guys who by boats and gear for them based on looks alone.

True story, I asked "what sort of boat have you got?", CB boatie answers "It just fits in a 14mt marina berth and is a black Riveria". Sadly that is about all he could tell me while he was trying to decide on an anchor. It gets worse, the wife made the final decision based on..... colour. She liked and wanted "that Yellow one but in Red!". Either they gave absolutly no indication that they heard a thing I said but actually did or the decision was actually based on colour. I did have to paint the yellow red for her. They were very happy. They luckily walked out with a good anchor (smile here Alain) but we were a tad gob smacked.
I did look quite good in red actually.

People like this we always talk upsizing the gear to save both themselves and the rest of boating public as well.

No matter what else, you must be happy when you climb in to the bunk!!. If this means 75lb anchor and 200mts of 12mm on a 35fter so be it. Going to sleep thinking "will my anchor hold" is not good in any way.

Chain is good. How much (size and length) is the question. I'd answer it is quite boat situation specific as is the anchor/rope and also a good discussion.

 

[craigsmith]

[ QUOTE ]
After studying in detail the referenced material it seems there is a misconception that the wind is the reason for anchor dragging.

[/ QUOTE ]Whoa. This is no misconception /forums/images/graemlins/laugh.gif

Your yacht's engine is not very powerful SolarNeil. Please, visit the site that Alain linked to, and play with the calculator, that will give you a rough idea of the forces that wind will generate.

It also considers the force of tide vs wind.

Wind is absolutely frequently the causing factor of dragging.

[ QUOTE ]
Water is easy. It is the waves hitting the boat.

[/ QUOTE ]Yes... but only if you're talking about long surges or big wave action on a small boat, otherwise the catenary of the chain or stretch of the rope will handle this.

[ QUOTE ]
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.

[/ QUOTE ]This is true. One of the reasons for using as much chain as possible. Although you have not mentioned that the chain also provides a dampening factor by virtue of its simple presence in the water and lying on the bottom; i.e. it is harder to drag around, so the boat's sailing is further reduced.

[ QUOTE ]
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.

[/ QUOTE ]Undoubtedly chain is good, the more the better, and 100% with a snubber is ideal. However, your conclusion is shaky. It is usually those less experienced who use only short lengths of chain, or none at all, and the fact that they are less experienced affects other aspects of their anchoring experience, including the type and size of anchor being used, how they set it, etc. So you cannot be sure that the chain is making <u>all</u> the difference.

(I sound like I'm arguing against myself, since I support the use of chain, but my point is it is not the sole deciding factor).

 

[duncan]

Gmac - Craig; great contributions.

Craig, given the thread title etc your observation about tandem is surely worth expounding on?

I can understand how it would enable a boat to use twice the anchor without having to handle one great beast all the time - is that the crux of it?

 

[Guest]

It IS definitely a "misconception that the wind is the reason for anchor dragging"

My engine is quite capable of moving the boat forward into very high winds. (I gave real examples). Therefore the force from the propeller is greater than the wind. So simply put; the spread sheet gestimations are way out and do not match my reality.

Also I have anchored for 10 years on the same 6mm three strand traditional line and chain hook. I have only broken it once (it got out of the fairlead). Therefore the forces on the anchor are way, way less than your web site and the spread sheets suggest.

Finally on to anchors and your video and tests. The Bruce was designed for a particular purpose in a very particular sea bed problem. It also has an inherent ability not to go mining. If the chain angle raises slightly then the blade angle turns through the horizontal and it rises to the surface. So put it in soft mud or sand and you get good holding without it disappearing from sight. It was never designed for hard sand. However, where I learnt to anchor has a ground consistency of thick porridge and so it was ideal.

The CQR has a good forward digging angle but then converts quickly to a sideways wedge to avoid to much downward tendency. The conversion I am talking about is the shaping of the wedge and the ears at the aft end. This gives it its good holding without it submerging too far. As is well demonstrated by your video. Breaking it out is just a matter of rotating it. Yes, I have buried it once and it took some effort to get it back.

The "modern" anchors are all variations of the slab chisel principle. They are wonderful diggers but have no control of their depth. This is demonstrated well by your promotional video. In soft material they will just keep digging as their chisel angle is large and is not reduced to zero by the small forces pushing up on the shank and chain. In the event of serious mining then the rotation of the anchor in the mud will leave it still completely underground. Therefore to break it free it will need a pulling power greater than its holding power.

So in the special case of medium soft bottoms you can end up after a long blow with your anchor buried so deep that its would be beyond the capability of the boat to free it. Anchor design is a compromise between uncontrolled burrowing and digging in the first place. So as I said earlier you use the right anchor for the job, or carry an average that will work in most places.

As for shank strengths I believe I remember a major world race where the skipper used the shank of a forged CQR sideways as a weight distribution system when the base of their mast started collapsing. I thought that was the best promotional picture ever of the strength of forged anchors.

Tomorrow, I finally get back to sailing and the real world; with my proven CQR, Bruce & fishermans anchors and 10mm chain. I sleep well.

And NO double anchors to slow down my escape.

That's all folks!

 

[craigsmith]

[ QUOTE ]
It IS definitely a "misconception that the wind is the reason for anchor dragging"

My engine is quite capable of moving the boat forward into very high winds. (I gave real examples). Therefore the force from the propeller is greater than the wind. So simply put; the spread sheet gestimations are way out and do not match my reality.

[/ QUOTE ]No. Sorry. For a start your propeller in reverse, when you are setting the anchor, will provide nothing like the power that it will in forward. Secondly when the boat is dead in the water its screw action is not optimal. Unless you are a tug you are unlikely to be able to properly test the anchor by using your engine (peeps, this is not to say the anchor should not be set by using whatever power you do have available).

As Alain has said, you may believe what you like, but it does not make it true. I am sure many forum members can relate to a gale coming through and their anchor letting go, even if it was set and the anchorage well sheltered from surge or fetch.

I do not wish to be confrontational SnowLeopard, but <u>to claim that the force of wind on a boat is negligible</u>, in the context of anchoring, is nonsense.

With specific regard to the work of M Fraysse: unless you can convincingly object to the use of the American Boat and Yacht Council data which forms the basis of his wind force figures, you have no right to reject the results as "not fitting in with your reality".

[ QUOTE ]
Also I have anchored for 10 years on the same 6mm three strand traditional line and chain hook. I have only broken it once (it got out of the fairlead). Therefore the forces on the anchor are way, way less than your web site and the spread sheets suggest.

[/ QUOTE ]Well I would suggest you try polyester octiplait as three-strand has nothing but disadvantages for anchor rode, but I get the impression you are happy with your set-up regardless of what I say. Perhaps GMac can offer some comments.

But anyway, although you don't give details, are you saying that your rode broke while the anchor was set? It broke <u>before the anchor dragged</u>? Doesn't that tell you something?

[ QUOTE ]
Finally on to anchors and your video and tests. ....

The CQR has a good forward digging angle but then converts quickly to a sideways wedge to avoid to much downward tendency. ....

The "modern" anchors are all variations of the slab chisel principle. They are wonderful diggers but have no control of their depth. ....

So in the special case of medium soft bottoms you can end up after a long blow with your anchor buried so deep that its would be beyond the capability of the boat to free it. ...

[/ QUOTE ]No, no, and NO /forums/images/graemlins/crazy.gif
but this thread is not about anchor types so let's not start another.

 

[GMac]

Wind does cause boats to drag.
Wave action also causes it.

Sitting anchored in an open area, I would like to put forward -
The boat will be fine unless the wind gets up to high speeds and then how the anchor system is sized/designed will dictate if it drags or not. The same boat on the same gear will drag from the same spot sooner due to the wave or tidal flow action getting stronger. If you have both wind and waves you will be gone even sooner.

By this I mean the water action will make a boat drag sooner than wind speed assuming the state of each is the same i.e the "weather is bloody awful". Not good terminology there but hopefully it makes a bit of sence. Could be put as 'bloody awful' water action is worse than 'bloody awful' wind action.

Only tamden anchored a few times and have used both 'in-line' and seperate rodes. Either is a pain in the bottom and used in the relms of extreme weather when you just do what you can with what you have an hope it works. The subject is like the anchor debates, what works for some does not for others.

Just pulled the anchoring gear off my latest boat (performance 9.3mt leadswinger, 2000kg disp) as it was a 35lb plow, 10mm chain and 16mm rope. Anyone with a 40fter need some good sized gear Not that the racing bug has bitten again but do you think 4mm Dyneema to 5mm chain could be a bit lite??

 

[Bejasus]

have got to say that this is one of the best anchoring threads I have read. Probably because it kept out of the 'which anchor' debate and just got down to the specifics of technique and the reasons for it.

Also enriched by the contributions of Hylas, Craig Smith and GMac

 

[hylass]

Re: Disagree with this

[ QUOTE ]
[ QUOTE ]
Attaching two anchors to one rode, known as tandem anchoring, should be avoided.

[/ QUOTE ]For the record, we absolutely disagree with this and advise the exact opposite

[/ QUOTE ]


Here is a letter from Jean Louis GOLDSCHMID, Former technical manager of the most prestigious French Nautical sailing school "Centre des Glénans" published in N° 114 of Glénans news letter (August 83) (“badly” translated from French)

<< The Tandem set technique it is a very good technique with Fisherman anchors and I personally made some experiment at time when the Glénans’s boats only had this type of anchors on board.

On the other hand,. I began one day to have doubts while seeing tandem set anchored boats dragging.

I thus carried out a series of measurements of traction with a motor boat. Almost all the tests gave the same results: one needed 200 rpm less to drag 2 tandem set anchors (CQR or Fluke anchors) than only one of these anchors alone. I thus checked what occurred, with small anchor on the dry maërl beach of “PEN MARYSE” in the Archipelago of Glénans, pulling by hand.

First problem with the CQR:, it doesn’t have any fixation hole to attach the second anchor (that should have been a sufficient reason for not using this technique), I thus tested the bar, the trip line hole, the elbow of the shank. On these 3 points. the effect is the same one: the articulation plays badly, the plow cannot dig in. Remain the extremity of the shank, but it is not better. Almost each time, the chain comes to obstruct the plow The whole system does hold only on the most distant anchor. If this one is smaller, it holds less than only the large anchor one.

I noted too that an anchor holds very badly in the furrow of another.

With the “Fluke” anchors: this is again the same problem of devoted fixation, and it does not have there anything which can be used except sometimes the trip line rings which are usually not strong enough. However, from time to time y obtained results comparable with the holding of only one anchor.

I thus concluded from it, that I had sufficiently poisoned my life by re-installed useless scrap heap to definitively give up the tandem set technique.

 

[craigsmith]

[ QUOTE ]
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?

[/ QUOTE ]Number 4, followed closely by number 2.

(Duncan you do not specify if #4 includes an additional length of chain between the two anchors, or if one of the anchors is just attached to the rode of the other. For the scope to remain the same the former has to be true, but this adds a bit of weight to the system).

Really the practical answer is #2, but I say #4 because of the following reasons:

1) The aft-most anchor acts as a kellet for the forward-most one, so the angle of pull is guaranteed to be horizontal (so it serves two purposes)
2) The sum of the blade area of two 1Kg anchors is greater than the blade area of one 2Kg anchor.

This is not to say we recommend this - the practical answer again is #2, because it eliminates complications. To re-iterate what I said in another post: tandem anchoring is for extreme situations. Size your primary anchor to be capable in anything but.

Then there are other issues such as the fact that a larger anchor may perform better than a smaller version if the substrate is layered (soft on top, hard down a ways) - even anchors of the same type can give varying performances depending on the seabed variables.

Gmac (who chose #3): 15 meters extra chain closer to the boat is not going to compensate for halving the size of the anchor. Did you really mean #3?

 

[duncan]

[ QUOTE ]
Quote:
--------------------------------------------------------------------------------

Also I have anchored for 10 years on the same 6mm three strand traditional line and chain hook. I have only broken it once (it got out of the fairlead). Therefore the forces on the anchor are way, way less than your web site and the spread sheets suggest.


--------------------------------------------------------------------------------

Well I would suggest you try polyester octiplait as three-strand has nothing but disadvantages for anchor rode, but I get the impression you are happy with your set-up regardless of what I say.

[/ QUOTE ]

I think you will find that this is his 'snubber' not the main part of the rode. I use the same arrangement and dimensions!

 

[GMac]

[ QUOTE ]

Gmac (who chose #3): 15 meters extra chain closer to the boat is not going to compensate for halving the size of the anchor. Did you really mean #3?

[/ QUOTE ]

Na.. I'm happy with no. 3. But within the parametres I mentioned in an earlier post. The problem with a list like that is no boat or useage is specified and that is very very important to whatever anchoring system is picked. As a 'general purpose' system for a 40ft boat as most are used down here I'm sticking with no. 3. I did mention I mentally swapped out the Delta for another anchor but we are not going there

No. 1 60kg anchor and 27mt x 8mm chain = waste of time and very boat performance negitive. Maybe just handy in a real big blow but you would want the best snubber ever invented. In no way can you call a 60kg anchor and 8mm chain a match, it does just not stack up. A 60kg anchor is for boats well above the size that use 8mm chain.

No. 2. OK on a offshore cruiser not being used in any corel areas. Very American sizing though but not as much as No. 1

No. 3. as mentioned above.

No. 4. Don't like having to use 2 anchors in any way. 2 anchors is for the extremest weather only when you have no other options. This excludes when used to keep bum of boat to beach, in rivers and the like.

No. 5 and 6. Angles/killets/etc are for people who don't have a good anchoring system to start with. I find them nothing but a pain in the botty and do consider them as being quite capable of getting people into a more dangerous place than they need to be. Angles themselves and some (note the word 'some') users of them make me nervous. Then again I know of one or two who think Angles are the greatest thing since mum caught her tits in the wringer.

As mentioned earlier, an anchoring system that is fine on one, say 40fter, may be c**p on the one next door. Each boat is differant as is each user and each users use. The system must be matched to all 3 to perform at its best also while being boat performance positive and user freindly. It is not a 'one size fits all' situation. General assumptions can be made for a general boat size range and use but get specific and things need to be tweaked to the indervidual situation.

Quick example - The anchoring system used on, say, Kiwi Roa (55ft offshore cruiser whos name I hope I spelled right) would be bloody ludicrously big on Formula 1 (65ft Race yacht) but the system used by F1 would be great on a 35ft offshore crusier or a 40ft coastal crusier/racer.

Another quick one - many US cruisers sail down to this end of the world and change up a size in anchoring gear (quite common). At home the gear they had was fine but down this way it's not. Generally they change up a size in chain and make it longer, usually keep the same anchors.

And 1 more - my new 31fter has 2 anchor rodes. One is 4mts of 7mm chain to 40 mts of 10mm rope to a alloy anchor. The other is 10mts of 8mm chain to 70mts of 12mm rope and a steel anchor. One rode is for racing and the other for cruising.

Horses for courses. My horse says No. 3 fits this course

To H00 - You're right this is a good thread, well done all.

 

[duncan]

[ QUOTE ]
60kg anchor and 27mt x 8mm chain = waste of time and very boat performance negitive

[/ QUOTE ]

as they all weigh exactly the same I am facinated by the boat performance negative comment.

overall the whole point of the comparison (which you have avoided with every comment!) is that you have 100kg to use and you are looking at the relative holding of the alternatives given.

No 1 has 93m of nylon rode as a snubber........not enough?

Yes I agree that the use of a common chain size gives some unbalanced, in the conventional sense, packages but as I have purchased your best quality 8mm chain ( /forums/images/graemlins/cool.gif) I would expect that even if it is the weakest point in no 1 overall this will deliver signifacently more holding power than No 3.

The most interesting observation yet was that from Craig pointing out that you won't get twice the holding out of an anchor twice the weight - this would certainly seem to provide support for the tandem approach in a prolonged blow from a constant direction where you can set them both effectively; or maybe it doesn't.

 

[craigsmith]

[ QUOTE ]
as they all weigh exactly the same I am facinated by the boat performance negative comment.

overall the whole point of the comparison (which you have avoided with every comment!) is that you have 100kg to use and you are looking at the relative holding of the alternatives given.

[/ QUOTE ]He is talking about the extra 20 or 40 kilos of weight stuck on the bow of the boat, which does adverse things to pitching moment and gives boat designers headaches. Better to have the weight in chain down below.

[ QUOTE ]
Yes I agree that the use of a common chain size gives some unbalanced, in the conventional sense, packages but as I have purchased your best quality 8mm chain ( /forums/images/graemlins/cool.gif) I would expect that even if it is the weakest point in no 1 overall this will deliver signifacently more holding power than No 3.

[/ QUOTE ]GMac's point is that it depends on several variables not included in this model. He claims that #3 will do better than our choice of #2 or #4 using the same logic. I submit that he is wrong with regard to us, #2 has to be the best balanced and most practical, but probably right with regard to #1. For example, if you use that set-up (#1) in soft mud, high wind forces will quickly make the rode angle equate to that of the scope, i.e. 6:1. This means that the rode force's vertical component is quite high, and the extra 40Kg isn't going to make much difference to dealing with that. Similarly if there are more shock loads to deal with (wave action? surge?), the rode will be less capable of handling it.

But, if you're talking about a well set anchor in hard sand and there's constant wind and no fetch or surge, then #1 could even possibly be the better choice.

What about anchoring on coral or flatbed rock? There's only a few cm of sand or mud, then solid stuff that no anchor will penetrate? Better have a heavy anchor...

[ QUOTE ]
The most interesting observation yet was that from Craig pointing out that you won't get twice the holding out of an anchor twice the weight - this would certainly seem to provide support for the tandem approach in a prolonged blow from a constant direction where you can set them both effectively; or maybe it doesn't.

[/ QUOTE ]You won't get twice the fluke area, but you may get twice the holding power, or even more. Seabeds are frequently layered, with soft sand or mud on top, and hard sand or clay below. A physically bigger anchor has a better chance at getting its tip down into the hard stuff.

So it provides support for splitting up anchor weights, but the practical balanced answer is still #2. And the real answer is you must size your primary anchor to meet all every day conditions, then have additional hooks to deal with the unusual. So in addition to your 40 you would have a 20 or 30 down in the bilges to use in a tandem rig /forums/images/graemlins/grin.gif - my point is you wouldn't have a 70.

Does that make sense?

/forums/images/graemlins/crazy.gif

Can we talk about which anchor is best now?

 

[GMac]

[ QUOTE ]
Can we talk about which anchor is best now?

[/ QUOTE ]

NO! /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif

G'day Duncan and all,

Sorry for wondering off there for a moment Duncan but an anchor system is not about 'max holding' only. If that was the case we would have some very funny looking boats out there with the sailing performance of bricks /forums/images/graemlins/laugh.gif

Craig hit it on the spot regarding the negitive performance comment. Way too much weight right on the pointy end in No.1 and that sized chain is just a waste of time, it won't do sweet F all in the big scheme. May as well just have a 100kg anchor and rope, probably work just the same. Yes 93mts would be about the length of the snubber you would need /forums/images/graemlins/laugh.gif So no.1 is neither balanced or practical, probably hold very well if you could live with all the downsides.

I would think no. 2 would probably have the best holding load, just, but at the expence of other things. Also probably hold more than required and nearly a 'hammer to open a peanut' option, 98% of the time. Again not balanced and marginally practical on a offshore crusier only.

The best all round most practical would still be no. 3. This is a well matched system which does work very well. That comment partly based on the fact that that is a very common system being used by many when No. 2 isn't.

If I had 100kg to get the best holding I would not be using any of the items in the list at all. I would have a 80kg Stingray (the rig ones not the danforth sort of ones) and 22mm PP/PT rope behind. Out hold all the other options by miles but practical?.... no way in hell.

[ QUOTE ]
I submit that he is wrong with regard to us, #2 has to be the best balanced and most practical

[/ QUOTE ]

Gezz you're sound a bit like a lawyer /forums/images/graemlins/grin.gif (last time I heard 'I submit' it nearly cost me piles of money) but 'the most practical' for what? Offshore cruising in a big boat with undersized chain, probably yes, just. Anything else = No. Balanced is not a word I'd use for that system, 40kg anchors and 8mm are not a good match. 20kg and 8mm is as is 40kg and 10mm chain.

[ QUOTE ]
A physically bigger anchor has a better chance at getting its tip down into the hard stuff.

[/ QUOTE ]

Wrong!!!! and yet still right. Going on that theory my 30fter should be sweet as on a 40kg anchor for anything. This would be right as long as the anchor is a very very good self-setter. If it was a Delta as in the example I would submit ( /forums/images/graemlins/grin.gif) that I would not have the horsepower to actually set the anchor so I would be hanging off an interesting lump of steel sitting on top of the seabed. If you slowly pull a Delta over a firm bottom it is very capable of just sliding along without setting, worse with a CQR. If the anchor is to big the boat can't set it and you have low holding. Actually I probably could set a 40kg but you catch my drift I hope.

[ QUOTE ]
And the real answer is you must size your primary anchor to meet all every day conditions, then have additional hooks to deal with the unusual.

[/ QUOTE ]
Exactly my point. Everyday + practical + balanced + 8mm chain = 20kg


I'd agree with Craig that 2 x 20kg should have better holding than 1 x 40kg in most cases, especially in the older designs.

I think a bit of what we have here is, and no disrespect or anything like that intended, some cruisers and then me who comes from a racing background with some cruising and dealing with many differing boats each day. Cruisers are nice people and like big, which is fine but racers, also mostly nice people, like small, which is also fine. General 'boating' people would want something in the middle and brings us back to 'horses for courses' again.

This is a good thread. Am I winning?? /forums/images/graemlins/laugh.gif /forums/images/graemlins/laugh.gif, I'd like to submit, I suspect I should not be holding my breath /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif