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-   -   Best dual anchor configuration? (https://www.cruisersforum.com/forums/f2/best-dual-anchor-configuration-192967.html)

Don C L 28-10-2017 09:49

Re: Best dual anchor configuration?
 
Yeah I really think once you have an adequate anchor, rode that won't chafe through (don't forget that one) and plenty of scope (10:1 or more) it is time to look at the fittings on the boat and see if they are really up to the task of holding the displacement of the boat if it is lurching, and being thrown back and really yanking on the rode. The cleat or post, of course need to be bomb proof, but I used to sail a boat that had the bow roller halfway out on the sprit. I never trusted that. Fortunately it had a beefy snubber that went to a good fitting at the waterline at the bow (which is also a good idea not mentioned yet.)

noelex 77 28-10-2017 11:04

Re: Best dual anchor configuration?
 
Quote:

Originally Posted by Jim Cate (Post 2507561)
The best dual anchor configuration is a better single anchor...

:) :).

It is hard to add a second anchor and increase the holding significantly over the better single anchor.

In a "V" configuration, as the boat sheers in the gusts the load will be applied to one anchor without much load sharing. As the boat swings the load will come on the other anchor and the boat "walks" backward dragging each anchor in turn until they let go completely. In a tandem arrangement there also tends to be little load sharing. Often one anchor is totally unset.

The drawbacks of two anchors are considerable. The extra weight of two anchors and two rodes is significant, much more than a slightly heavier single anchor. In a V configuration you will swing differently to other boats, there is a risk of the rodes becoming tangled. Most critically if you do drag, recovering two rodes especially two tangled rodes (and in all probability they will be tangled) can be difficult. If you ditch the lot you are down to using your third anchor.

There are some advantages:
When at anchor and very bad weather is forecast most people feel compelled to do something. Setting a second anchor feels very constructive and is perhaps better than simply worrying about the weather. There are other things that be done but they just dont have have the feel good factor of deploying a second anchor. It is easy to pretend that your holding power is now double, although most realise this is a fallacy.

On a more practical note, two anchors do reduce sheering. There are other ways to reduce sheering and these may be more effective and easier. On most boats the effect of two anchors is not great, but some boats report more significant benefits so it is worth some experimentation.

So I am not a great fan of two anchors designed to be used in heavy weather, although there are plenty of other practical uses to two anchors such as to point the bow into the swell, or to reduce the swinging area.

Having said the above, if facing something like a named storm, especially if leaving the boat, you may as well put out all the anchors you have.

NevisDog 28-10-2017 12:01

Re: Best dual anchor configuration?
 
Quote:

Originally Posted by thinwater (Post 2507583)
The truth is that it depends.
...
...I have a book coming out this winter.
----
Hammer lock. Really, the only good use for a smaller anchor.
...

Sounds like this guy really knows his stuff, so I went searching for 'hammerlock anchoring,' which led me to "anchoring 201" at captfklanier.com. Now I thought I knew a little bit about this subject but I sure never heard of "drudging" before (which is exactly what Thinwater was rather cryptically referring to above).

So, if you don't have that 40kg beast and only have a large and small anchor to keep you safe through that unexpected storm, I suggest you read up on 'drudging' and the like, or better still, Thinwater may tell us the name of his forthcoming book?

Personally, I find the greatest shock-loads are imposed by the vessel 'sailing' about under a single anchor, so, though a second anchor may not provide much extra holding power, it can greatly reduce the loads as the boat comes up hard on one tack and swings back on the other.

Navicula 28-10-2017 12:15

Re: Best dual anchor configuration?
 
having 2 anchors is great......if one get fouled like a previous post suggested, you can drop that one and re hook somewhere safe and come dive on it later....

I recived a great tip in the bahamas .....have a method to let the chain go at the bitter end....most, like mine are shackled to the boat and the shackle wired up so it does not come undone.....replace the shackle with a strap or rope to the bitter end so if its blowing and your dragging and tangled up with others you will be able to cut the strap with a knife with easy and set yourself free

NevisDog 28-10-2017 12:22

Re: Best dual anchor configuration?
 
Quote:

Originally Posted by Navicula (Post 2508000)
.....have a method to let the chain go at the bitter end....most, like mine are shackled to the boat ...

Never, ever, shackle the bitter end to the boat!!! (Anchoring 101).

Don C L 28-10-2017 12:29

Re: Best dual anchor configuration?
 
I hadn't heard of hammer lock either, had to look it up. I'm not sure drudging and hammer lock are strictly speaking the same thing though they do share dragging an anchor on purpose. Hammer lock involves dropping a second, smaller hook from the bow on a short scope, I see, to dampen the sailing at anchor, once the 2:1 slack is taken up on each tack. I gather you'd want to set the smaller hook a bit aft of the bow to minimize chance of fouling the main rode on the unset smaller anchor when the weather is calm.

Don C L 28-10-2017 12:42

Re: Best dual anchor configuration?
 
Quote:

Originally Posted by Navicula (Post 2508000)
having 2 anchors is great......if one get fouled like a previous post suggested, you can drop that one and re hook somewhere safe and come dive on it later....

I recived a great tip in the bahamas .....have a method to let the chain go at the bitter end....most, like mine are shackled to the boat and the shackle wired up so it does not come undone.....replace the shackle with a strap or rope to the bitter end so if its blowing and your dragging and tangled up with others you will be able to cut the strap with a knife with easy and set yourself free

and if you have all chain keep a length of line 50 or 60' or so with a buoy and carabiner on it to quickly clip on to that bitter end if you ever want to retrieve it again without diving. If you have nylon rode, just keep a buoy handy. Had to do that a couple times. Or keep a grappling hook on board for it. Buoy is much easier.

captstu 28-10-2017 13:08

Re: Best dual anchor configuration?
 
50 years Anchoring experience including diving on the anchors probably 30 times give me some confidence that tandom anchor is the way to go.

Let me share one anecdote that is typical of my experience.

Hurricane Wilma Passed over North Palm Beach with more wind than I felt I can safely endure on board. I anchored my boat, a 43 foot voyage catamaran, with a tandem anchor consisting of a 25 kg Bruce backed by an FX 37 fortress. The heavier anchor was attached to the boat with 100 feet of 5/16 HT chain and 2 bridles. Primary bridal was 5/8 nylon spliced to the boats beam and hook to the chain with a Wichad Chaim hook. The secondary, bridle was attached to two cleats some chafing gear and rolling hitch on the anchor chain.

At the end of the storm both bridals broke at both ends. The rolling yet remain attached to the chain and the chain hook also rebate attached to portions of the primary bridle and the chain. There was no apparent chafe. I believe the lines broke when the the Eye passed over the boat and the beer passed over the boat causing her to run down the shade and lurch to a stop suddenly.

The chain pulled the windless out of It’s mount . The chain had an overhand knot just before the hard point where the bitter end was attached. The bitter end attachment snapped out of builders Hard point, and the chain knot jammed the hawse pipe saving the boat.

I dived the rig before recovering. The primary anchor, the Bruce, showed signs of tripping when the veer hit the Boat. All that was visible of the fortress was the chain where it attached to the Bruce. The chain was about 6 feet long and completely buried.

I was able to recover the Bruce with the windless and some help from a spare halyard. It took several hours of motoring To recover the remains of the fortress. When the veer hit The shank of the fortress bent 180į And the flukes were both destroyed.

Virtually every other boat in a crowd of anchorage was up on the beach.

Other than a broken winless about, two broken bridles, and a chain that it stretched itself in the near uselessness with the overload, my boat took no damage.

While this may be an anecdotal story it is not the only time that I survive moderate to heavy winds on a tandem anchor set While the boats around me using more sophisticated anchoring systems either drifted away or in some cases were rescued when I throw line to them And allowed them to trail off of mine till the wind died down.

Fortress replaced the damage parts for free under warranty and Bruce was not damaged.

NevisDog 28-10-2017 14:20

Re: Best dual anchor configuration?
 
Quote:

Originally Posted by captstu (Post 2508033)
...I dived the rig before recovering. The primary anchor, the Bruce, showed signs of tripping when the veer hit the Boat. All that was visible of the fortress was the chain where it attached to the Bruce. The chain was about 6 feet long and completely buried.
... It took several hours of motoring To recover the remains of the fortress. When the veer hit The shank of the fortress bent 180į And the flukes were both destroyed. ...

This is an absolutely fascinating story, one that deserves most careful evaluation (which I'm sure Capt Stu has already done) and I hope I can be forgiven for attempting to analyse it further to see what I can learn from this once-in-a-lifetime experience (well, for me, once would be more than enough!).

I've picked only those sections that I find most concerning, though the entire story deserves reading again.

1. "All that was visible of the Fortress was the chain where it attached to the Bruce" and "the Bruce showed signs of tripping": This suggests to me that, had this been a single anchor moor (the Fortress alone, without the Bruce) then it would most likely have buried deeper than the six feet of chain it was allowed from the Bruce. It suggests to me that having the Bruce in tandem actually hindered the Fortress's well-known ability to keep on burying until it can never be recovered.

2. "The Fortress shank bent 180 degrees and the flukes were both destroyed": seems to me the only thing that saved the boat was the Fortress being buried deep enough so that in its mangled state it still had enough holding due to the depth of bury of this mangled lump of twisted metal. But I again suggest the Bruce in tandem actually restricted its ability to bury.

I would conclude that the big Fortress alone would have been more effective than the tandem set-up. I'd also speculate that a bahamian-type moor might have prevented the damage inflicted on the Fortress; it seems fortunate indeed that such damage didn't result in it letting go or snapping off, leaving the Bruce to drag along just below the surface (as it is well known to do).

But this is all just idle speculation on my part - I wasn't there to witness any of this. I take it that Capt Stu reached entirely different conclusions, as it seems he still favours tandem anchoring, and I'd love to hear his reasoning.

thinwater 28-10-2017 15:06

Re: Best dual anchor configuration?
 
Quote:

Originally Posted by barnakiel (Post 2507821)
Yes.

Probably a lot depends on what the configuration is (e.g. which anchor goes up first: the small, or the big one, or are they both big anchors, etc.) as well as on the bottom (sand, mud, or rock, or weed). There are many factors.

I think tandem is difficult to lay out too. One may want to have No1 dig in very well and then No2 just as well. But if they are chained, No2 may become next to impossible to set as No 1 will keep the rode tight and the No2 immobile. If No2 is immobile, it cannot dig in.

If we reverse the situation and use a smaller 'pilot' No1, then No2 may dig in, but what is the use of No1 then?

Etc.

I have no doubt tandem may work with good skills and in some situations but it does seem more difficult to deploy well.

b.


Try it. Then dive on the anchors. Then tell us what you see after a shift.

I've tried it, lots. Every anchor manufacture, including oil rig anchor manufactures, will tell you it does not and cannot work.

Try it.

TheThunderbird 28-10-2017 17:38

Re: Best dual anchor configuration?
 
If you believe that you should deploy two anchors, first add 20# to your primary anchor.

A second anchor can be used as a kellet hanging on the rode and softening jerks..

'Course, in a shitless situation a Tandem anchoring can give you some psychological Peace of Mind

V-setting will never work with 2 anchors at once, and IF they do, one is unnecessary.

Sheering and sailing on anchor is stressing both me and her.... I find a brilliant solution, by means of taking the snubber out, over one side, at the bow or even more aft, thus allowing for some righting force.

The side to choose depends on boat and on local circumstances

They used to have heavy and cheap storm anchors. We may agree that on a leisure vessel it is impractical or dangerous. The second anchor must be a spare, and an alternative for different grounds

captstu 28-10-2017 18:48

Re: Best dual anchor configuration?
 
Some comments on the comments if I babe.

I tried various lengths of chain between the primary Bruce at the secondary fortress. I settlrd around 6 feet because it was easy to recover and easy to lay out.

When I know Iím going to deploy two anchors, I go forward as I enter the Anchorage at low speed and throw the fortress over the bow. It hangs below the deck above the bottom and does nothing until I bring the boat to a stop. At this point Iíd apply enough chain with the wetlands so that the fortress hits bottom as I begin to drift backwards. Once I feel the fortress it I slowly deploy chain in the usual manner until the last of shade I decided has been deployed.

At that point I wait until the boat Works is to stop.

I go forward the second time attach the primary bridal and played a short chain until the bridal is taught in there is significant slack in the chain between the bridal in the Bow roller.

I believe but cannot verify that the Bruce is acting as a way to keep the Fortress shank parallel to the bottom.

I donít actually bother to back what the set up because it is never ever felt the hold.

If I use more than 6 feet of chain fortress would hit the bottom before I was ready.

Recovery is Perform in reverse. I go forward release the bridal and motor forward to trip the Bruce. Once the Bruce is tripped I can recover it one to the power roller tripping the fortress of the process. Itís a fortress does not trip, I cannot completely recover the Bruce and bus go forward reattach the bridal at power forward until the unit trips. This is happened a few times

I have no problem with the idea that the fortress became a sacrificial anchored in a hurricane Wilma. My chain became sacrificial as well as that both of my bridals.

If I were to use just a fortress I donít think the weight of the fortress and Chain would be sufficient to stop for Fortress from flying rather grabbing.

I thought about adding weight to the chain to make the Fortres operate alone, But it made no sense since on some bottoms I have to use the fortress in the Bruce operates as a weigh only. It makes no sense to change over rather use both.

I understand that under the most severe conditions the Bruce. The fortress from going further down. I believe it is 6 feet down the fortress will hold whatever stress my chain set up can support

One caution, my experience may not be your experience. Solutions that work for Me may not work under the Unique conditions that you see.

IslandHopper 28-10-2017 19:37

Re: Best dual anchor configuration?
 
Quote:

Originally Posted by thinwater (Post 2508100)
Try it. Then dive on the anchors. Then tell us what you see after a shift.

I've tried it, lots. Every anchor manufacture, including oil rig anchor manufactures, will tell you it does not and cannot work.

Try it.

While i'm firmly in your camp re tandem anchors on our boats, i have to disagree re rigs and other offshore use.

We routinely use tandem (piggyback been the correct term) anchor setups when the situation demands, BUT, it's a very involved and time consuming process that can take easily a week to complete a whole spread.

When doing a whole spread (up to 8 piggyback sets) these are usually prelaid and tensioned in a straight pull by the anchor handler, long before the rig is even on site, this can take hours for each set and may have to be repeated if they don't set correctly, longest i have sat on one was just under 6 hours with about 90t tension on it until it set and the surveyor was happy.

When all are done and the surveyor is happy they are well "soaked" in, the rig is manoeuvred into position and connected to the free ends and snugged up to there working tension, then they will sit and monitor until happy that all is stable before starting drilling.

As i said it's a very involved exercise and the above description is massively simplified, but the point i'm making is it is used quite often when needed, I couldn't tell you how many times I've been involved in the operation over the years.

But for our use i agree, any lateral pull tends to upset the primary and fails to reset, in my experience anyhow :smile:

billknny 28-10-2017 19:49

Re: Best dual anchor configuration?
 
Quote:

Originally Posted by kas_1611 (Post 2507857)
And I thought I was mad with my 33kg Vulcan on my 40ft boat :biggrin:




Agree with you. Better to have a single bower that can handle everything Mama Nature could throw at you than have to mess around with multiple chains, anchors, shackles, snubbers etc. As I say "Go big or go home!"

You know your anchor is big enough for long-term, remote, ocean cruising when people walking down the dock point at it and laugh.

Nobody, but nobody, ever work up at 2AM in a storm and stayed awake because they were worried that their anchor was too big!

If you are fussing around with other complex arrangements involving kellets, tandem anchors, etc., you already have decided your main anchor is not big enough.

thinwater 28-10-2017 19:53

Re: Best dual anchor configuration?
 
Quote:

Originally Posted by IslandHopper (Post 2508330)
While i'm firmly in your camp re tandem anchors on our boats, i have to disagree re rigs and other offshore use.

We routinely use tandem (piggyback been the correct term) anchor setups when the situation demands, BUT, it's a very involved and time consuming process that can take easily a week to complete a whole spread.

When doing a whole spread (up to 8 piggyback sets) these are usually prelaid and tensioned in a straight pull by the anchor handler, long before the rig is even on site, this can take hours for each set and may have to be repeated if they don't set correctly, longest i have sat on one was just under 6 hours with about 90t tension on it until it set and the surveyor was happy.

When all are done and the surveyor is happy they are well "soaked" in, the rig is manoeuvred into position and connected to the free ends and snugged up to there working tension, then they will sit and monitor until happy that all is stable before starting drilling.

As i said it's a very involved exercise and the above description is massively simplified, but the point i'm making is it is used quite often when needed, I couldn't tell you how many times I've been involved in the operation over the years.

But for our use i agree, any lateral pull tends to upset the primary and fails to reset, in my experience anyhow :smile:

I should have been more clear. They will tell you it will not work in a shift. A spread means no shift.

Also, some of the rig anchor companies (Vyrhof) no longer attach the secondary to the tail of the primary, they attach it to the shackle because that is more stable. So the thinking is changing.

Define "when needed." Too my understanding, it is generally when a larger anchor cannot penetrate deeply do to deep soil conditions. This is more likely for large anchors than for sailors. Sailors, on the other hand, nearly always need more penetration. So the factors are reversed. That said, on of the situations where in-line tandems can excel is sand over hardpan and similar situations where the anchors cannot deeply set and are struggling for friction. There are times when in-line tandems make sense, but they are rare and the sailor needs to save the in-line rig for those times.


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