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Old 18-05-2015, 06:21   #31
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Re: How do you run two anchors?

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^^ Antarctic bottoms are ground up rock . . . . In some places very finely ground = thick mud, in others medium ground = gravel, and in others course ground = large stones. Often the "mud" is very stiff to completely frozen. The thickness of this ground layer varies (from very thin an inch or two to quite deep a meter or two) but is then most always over a pretty smooth solid sheet of rock. And there is often some thick kelp.

It's about as different from Chesapeake bottom as you can get.
I think that may explain everything.

There are 2 cases where a single-line tandem will be the best answer. Straight line pull (often as part of a multi-point mooring, which is a sort of advanced V). And a bottom where setting is unreliable, and hooking and friction are all you get. In the latter case, a single line (tangle free) with large anchors makes more sense than a V where one leg is likely to collapse, leading to fouling and dragging. It is probably also easier, once they get the rythym of doing it regularly.

Interestingly, it requires throwing all of the conventional burying anchor engineering out the window. Different math.

Thanks!
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Old 18-05-2015, 18:18   #32
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Re: How do you run two anchors?

Kellets are a great alternative to double anchors on a single rode, as they're very easy to manage.

Kellets are just weight on a shackle that keeps the chain on the sea floor. The chain does a lot of the holding work, especially when you have to use a shorter scope.

I use a 10 lb. grapnel on a shackle. If it seems necessary (due to heavy seas, hunting, or proximity) I'll just send a kellet down the rode. As the boat heaves against the rode, the kellet will find its way to the chain end, where it holds it down and keeps it set.

It does add weight to the retrieval, but you can send it down with its own small retrieval line attached to bring it up separately if you're retrieving by hand.

I use the kellet in deep sand bottoms or whenever I have to go below a 7:1 scope.


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Old 19-05-2015, 12:59   #33
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Re: How do you run two anchors?

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Kellets are a great alternative to double anchors on a single rode, as they're very easy to manage.

Kellets are just weight on a shackle that keeps the chain on the sea floor. The chain does a lot of the holding work, especially when you have to use a shorter scope.

I use a 10 lb. grapnel on a shackle. If it seems necessary (due to heavy seas, hunting, or proximity) I'll just send a kellet down the rode. As the boat heaves against the rode, the kellet will find its way to the chain end, where it holds it down and keeps it set.

It does add weight to the retrieval, but you can send it down with its own small retrieval line attached to bring it up separately if you're retrieving by hand.

I use the kellet in deep sand bottoms or whenever I have to go below a 7:1 scope.


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While a 10-pound kellet might help keep the chain down in light conditions, I think you will find the practice has been discredited as traditional folklore in strong winds. As soon as the load reaches 1000 pounds (which isn't much) it might as well not be there at all, and they've been know to whip around, causing tangles.

Easier to use a heavier chain or a bigger anchor, and more effective.
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Old 19-05-2015, 13:26   #34
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Re: How do you run two anchors?

We carry two plow-style anchors on the bow.

I have found a few occasions where deploying both was desirable.

One was in a bay exposed to the north with winds from the east. We effectively deployed one off the stern (main rode was to the bow, but tension was taken through a stern chock to a winch to adjust) to keep the boat pointed into the swell. It was *much* more comfortable that way.

I have assisted in the deployment and retrieval of multiple anchors for purposes of weathering a hurricane. I cannot say that it was necessary, but that boat did survive a direct hit from a Cat 2 hurricane. The bow roller was rather torn up, though.
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Old 19-05-2015, 14:29   #35
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Re: How do you run two anchors?

Assuming we are not talking about compensating for either an expected dramatic wind shift (e.g. hurricane) with a V off the bow, or specialized circumstances where a tandem anchor off the bow makes sense, but are talking about a stern anchor to hold the boat in position or orientation, the approach we have found that works well for us is:

- Primary anchor - modern anchor on all chain with Windlass
- Secondary anchor - modern aluminium light weight anchor (our case AL Spade) on 10m chain + rope road
- dinghy easily deployed
- twin engined catamaran

To deploy we:
- drop the primary where we want it.
- back the boat to where we want it and hold it there with the twin engines if necessary
- flake the secondary rode into the dinghy, and then the anchor
- drive the dinghy to where we want the anchor and drop the anchor
- drive the dinghy back to the boat, laying out the rode
- bring the secondary rode onto the boat, pull it tight by hand to straighten the rode and cleat it off
- engine to netural, the boat will settle forward on the chain primary, setting the stern anchor, you can motor forward to check the stern anchor is set as well if necessary

To retrieve:
- tie a float on the end of the stern anchor rode and let it go
- retrieve the primary as normal
- motor to the secondary float, pick it up over the bow, and bring up the anchor using the windlass drum
- stow the secondary

This has a bunch of pro's and con's:
- you have to deploy the dinghy, which is easy for us as it is on davits ready to go, but won't be for everyone
- putting the rode and anchor in the dinghy rather than just the anchor and feeding the rode out from the boat, makes it a one person operation from the dinghy, rather than a two person operation requiring boat/dinghy coordination and keeps the secondary rode away from the props
- you don't need extra primary scope to allow you to drop all the way back to the secondary
- letting go of your secondary with a float feels strange/risky, but we've had no problems
- you can use your bow windlass and roller to bring up the secondary where you already have rode handling set up, and are less likely to bang up the boat or your back than bringing an anchor and rode in over the stern
- doesn't require any special stern anchoring gear other than a cleat

We didn't invent this method, we've just refined it over time by watching lots of other boats, most recently watching the small cruise ships in the Galapagos. I'm sure there are other ways that work better for others, just offering this as some ideas for consideration, when working out what works best for you.

Mark.
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Old 19-05-2015, 14:50   #36
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Re: How do you run two anchors?

^^ While there are several things I do just a bit different (different ships, different long splices....), there is only one real difference:

I've found it handier to clip a long line on to the secondary while I retrieve the primary, particularly when I am alone. In that way I do not have to pick up the float. The down side is you need to keep track of the line and the props. Just a single-hander's difference.
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Old 19-05-2015, 16:00   #37
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Re: How do you run two anchors?

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Originally Posted by estarzinger View Post

There are apparently tandoms used in deep rig drilling. I don't know in what specific situations.
For Evans interest, tandom (piggy back) anchoring is generally avoided. It's expensive (takes time to deploy, and the rig owner has to rent the anchors).

Never seen them used in deep water anchoring (800m to 2200m water depth), as the typical Bruce or Vryhov anchor will dig itself well in due to the weight of the suspended chain catenary.

Where I have deployed them is shallow to medium water depth, up to 500m, and only then after all other options are used up, which includes re-running the anchor, lifting the anchor to make sure it is not fouled, or changing fluke angles.
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Old 20-05-2015, 08:01   #38
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Re: How do you run two anchors?

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Well, I went over my edit time limit.

  • Many will not be able to use their highest holding anchor (Fortress).
(Same experiment as before, but this time it is a very capable Mantus anchor that the Guardian has lifted from a good set (note that I added a low tandem hole, per Rocna--it won't matter that much in this test). As Peter Smith explained, both anchors must have the same drag characteristics. The secondary should be smaller and drag more easily, so basically, you don't gain much. And even if the Primary did stay in the ground, the rules of mechanics and deformable bodies dictate that it will not be carrying any significant load, because the pivoting fluke anchor is "stiffer.")

Thinwater, can you post a link to your testing?

I am particularly interested in what amount of pulling force hauls the primary out of the bottom. Seems to me that's got to be a very large load. Is it within realistic loads for mid sized boat anchoring (IMHO, most estimates are way over stated)?

Anecdotally (no structured testing), Ive used inline tandem anchors successfully (didn't drag), but who knows without structured testing...the primary alone may have still done the job.
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Old 20-05-2015, 08:14   #39
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Re: How do you run two anchors?

FWIW, I'm in the multi anchors camp. Not so much for increased holding, where I agree a big-ass primary is probably the better solution in most situations, but there are anchoring scenarios where only multiple anchors will work.

For example: limited swing room or holding the bow into swell not aligned with wind.

When big winds are expected, I prefer to head for a nice cozy hole in the mangroves. In the unlikely event I drag in this well protected venue, all Im going to do is layup against the very forgiving mangroves.

Another use: multihulls with fixed keels, and some fin keeled monos, will walk around like crazy when wind and current are opposed. Ive used multiple anchors to limit walk-about range in this scenario too.

Ive used multiple anchors twice this season: once to anchor in a beautiful, but narrow cut, and another time to limit walk-about when wind and current went 180 oppossed. In that scenario a Catana was anchored nearby with their boards up. My boat has fixed keels. We went 180 degrees opposed to each other and were getting closer than I liked. I wanted to sleep well, so backed down on my primary rode until well out of their swing range and set a Bahamian Moor (easy to do)...slept like a baby knowing we could not go bump in the night.
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Old 20-05-2015, 08:24   #40
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Re: How do you run two anchors?

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How 2 avoid tangles with 2 anchors on 2 rodes? While there are many ways to deploy 2 anchors, the trick to avoiding tangles if the boat spins is to terminated the second rode to the primary rode about 4-6 feet below the bow roller, and bring only ONE rode on to the boat. If the boat spins, the single rode can absorb that without tangles. Not theory, I have done this many dozens of times without incident.
After several multiple anchor fiascos, I would like to try this technique. However, for those with rope rodes for their secondary, how would you propose attaching the secondary rope rode to the primary chain? Not many multis carry two all chain rodes.
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Old 20-05-2015, 08:55   #41
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Re: How do you run two anchors?

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After several multiple anchor fiascos, I would like to try this technique. However, for those with rope rodes for their secondary, how would you propose attaching the secondary rope rode to the primary chain? Not many multis carry two all chain rodes.
We use a loop of dyneema/polyester double braid to attach our bridle to our chain. It would be a simple matter to add another loop the the bridle and attach this to the rope rode of a second anchor. The loop is made by tying a double fisherman's bend (Double Fisherman's Bend | How to tie a Double Fisherman's, or Grapevine, Bend | Rescue Knots..) and is attached to the bridle with a prusik hitch (Prusik Knot | How to tie the Prusik Knot | Climbing Knots), locating the fisherman's bend in the middle of the prusik. The bight of the loop is then tied to the chain (or rope) with a rolling hitch. The diameter of the loop of dyneema is less than that of the chain or rope which aids in holding. Also, using a loop to tie the rolling hitch doubles the turns around the chain/rope from 3 to 6. I also put a figure 8 in the end of the loop just to be sure it does not pull through, but this is probably unnecessary paranoia.
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Old 20-05-2015, 13:14   #42
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Re: How do you run two anchors?

Cat Tales (35' light cat) has two 16 km Brittanys; one on 120 feet of 10 mm chain and 100 feet of heavy nylon, and the other on 65 feet of chain and 100 feet of nylon.

Only if the wind is high, and the chance of doing a 360 is very low, will we follow Don Street's advice and deploy two anchors. We hook up the first with all the chain out and connect it to the heavy nylon bridle. We then sidle up to (or beyond) the anchor but at least 20 feet to one side and deploy the second anchor. When we drop back, we have all 65 feet of chain and at least 40 feet of nylon out. We keep the second anchor's nylon rode on the roller, and tie it to the cleat beside the windlass, in the centre of the boat. As the second anchor rode assembly is more springy than the first, it seems to work well, allowing the boat to ride on the first anchor's bridle smoothly, while allowing some load transfer to the second anchor.

A note about the nylon part of both anchor rodes: We have become somewhat familiar with a special knot invented by Eric Tabarly that can be used to tie a loop onto a continuous rode or line for us to use to connect to a bridle hook or shackle. I cannot draw it, but have a picture on board to refresh my memory whenever I need it.
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Old 23-05-2015, 05:36   #43
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Re: How do you run two anchors?

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For Evans interest, tandom (piggy back) anchoring is generally avoided. It's expensive (takes time to deploy, and the rig owner has to rent the anchors).

Never seen them used in deep water anchoring (800m to 2200m water depth), as the typical Bruce or Vryhov anchor will dig itself well in due to the weight of the suspended chain catenary.

Where I have deployed them is shallow to medium water depth, up to 500m, and only then after all other options are used up, which includes re-running the anchor, lifting the anchor to make sure it is not fouled, or changing fluke angles.
Interesting. Thanks. I take it from this (while you use it as a last resort because of the cost) that it is believed that the tandom/piggyback does in fact increase holding power better than setting that second anchor out on its own separate rode?
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Old 23-05-2015, 10:11   #44
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Re: How do you run two anchors?

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Interesting. Thanks. I take it from this (while you use it as a last resort because of the cost) that it is believed that the tandom/piggyback does in fact increase holding power better than setting that second anchor out on its own separate rode?

Most rigs set 8 anchors, a few set 10, if one does not hold, they are not able an additional anchor, they have run out of fairleads, so the only option, after all else fails, is to rig a piggyback anchor.
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Old 23-05-2015, 14:08   #45
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Re: How do you run two anchors?

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After several multiple anchor fiascos, I would like to try this technique. However, for those with rope rodes for their secondary, how would you propose attaching the secondary rope rode to the primary chain? Not many multis carry two all chain rodes.

A screw-pin shackle? Seems rather simple to me.


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