Tandem anchoring

[Delfin]

The is worth a read as a primer for good anchoring technique, as well as the best discussion of how to deploy a tandem anchor setup I have seen.* Perhaps the most important take away is that without a specific hole in the primary anchor to which a tandem can be attached, the use of a tandem will/can result in a failure to set of the primary.

http://www.petersmith.net.nz/boat-anchors/tandem-anchoring.php

 

[skipperdude]

Alain Poiarud. Of The complete Anchoring Handbook. States He dropped tandom anchors 70 times in the waters of the med . He dove on all anchorings and states only 62%of the time did both anchors set.
*He further indicates that you should use only two of the same anchors
*Each anchor should be able to accommodating the load of your boat
*10 to 16 ft of chain should seperate the anchors.
*Never attach the chain to the first anchor

* All in all the book reccomends not to use a tandem anchor setup.

The hammerlock is moor advised.* After setting the primary, motor towards the first anchor, drop the second anchor*2:1 scope. It minimizes the swaying motion of a vessel at anchor. The second anchor is ready to become the primary anchor if the first anchor drags.

SD**

-- Edited by skipperdude on Wednesday 30th of June 2010 01:26:56 PM

-- Edited by skipperdude on Wednesday 30th of June 2010 01:28:32 PM

-- Edited by skipperdude on Wednesday 30th of June 2010 01:29:28 PM

 

[Delfin]

I suppose if you have the choice between doing something incorrectly that may threaten your boat or not doing it at all, best not to do it.* With respect to Mssr. Poiarud, both anchors are not supposed to set, unless the primary drags.* Perhaps 62% of the time, the boat didn't drag, or the tandem wasn't needed.* Little hard to tell, but I think he missed the concept completely, based on his comments.

To deploy a tandem anchor correctly you need a couple of things.* First, a primary anchor designed to accept a tandem in a way that doesn't prevent the primary from setting at all.* Absent that, a chain setup whereby the rode splits from the primary forward of the primary with a secondary rode leading back to the tandem.* This is a bit dicey, since it introduces the possibility of fouling the primary with the secondary rode when dropping the anchor in the first place.* Second, you need enough chain length between the primary and the tandem so that the primary can be properly set without engaging the tandem at all.* It should only set if the primary drags, which is kind of the whole point of the arrangement.

If you read Mssr. Poiarud's description of how he attempted to deploy a tandem and the anchors he used, it's not too surprising he concluded it didn't work.* That view is contradicted by many others, and the link explains to do job correctly.

The "hammerlock" mooring Poiarud reccommends is the bahamian mooring, which has its own problems, not the least of which is that it is a major pain to deploy and retrieve, as anyone who has used it can attest.* The other problem with a bahamian moor is that the load on the two rodes is never balanced.* The boat pulls and drags one anchor, veers and then pulls and drags the other, ending up with a birdsnest of chain and anchors as that situation unfolds that doesn't hold the boat particularly well.

 

[Keith]

Help me here. Why would you use a tandem setup if you had a large enough anchor already? Is this just a make-do situation if you had a bunch of smaller anchors on board?

 

[wingspar]

Dragging? Whats that? I use the SuperMax.

I remember now, that what other anchors do.

-- Edited by wingspar on Wednesday 30th of June 2010 04:58:17 PM

 

[Egregious]

Anchoring is a trade off like everything else.* Some set more easily but don't hold as well, and others hold well but are harder to set.* Depending on bottom conditions of course.*

My theory is get an anchor that sets well (Bruce) and make it twice as heavy as recomended so it holds better.* Instead of setting two anchors, just set one big ass anchor.

Somebody please provide data about how well a poor holding anchor performs if you just add weight to it.* I'm here to learn, thanks.

Woody

 

[Nomad Willy]

I'm w you Keith. Most folks have a storm anchor for the big blow and most storm anchors are the Fortress. This whole thing is only going to work w lots of scope and of course if it was going to blow hard one would employ lots of scope anyway. This is written by Peter Smith * *..the guy that designed the Rocna. His anchor is great (if and only if one has lots of room for scope). I don't like the guy. He talks frequently of utter truths that (most often) I think is no more than Peter Smith opinion. Addressing a threatening situation with the assumption that an anchor is going to set itself and not effect the performance of of the primary anchor is not good judgement from a seamanship point of view. One of the reasons I didn't buy his anchor is that he seems so stuffed w himself. He says "Danforth types including the Fortress are shocking" (whatever that means) "and are absolutely to be avoided. They are not general purpose anchors, and have no place in a tandem rig." Nuts. Absolutely NUTS. He's calling the most popular anchor in the world "not a general purpose anchor". I could see if you had 20-1 scope and could set the anchors simultaneously (obviously almost impossible) tandem would work but I'm not going to risk my boat that way. I think Alain Poiarud is probably right * * .. NOT RECOMMENDED.*

Eric Henning

 

[Delfin]

If you ask 5 boaters about anchors, you'll get 6 opinions.* Partly this is because testing anchors must be tough since you get very different results depending on the conditions of testing.* For example, the Super Maxx looks mediocre in some tests, and great in others.* The Bruce usually performs poorly in tests, but not all.* People tend to love what they have, unless it has failed them, and most boaters don't cruise where the outer limits of the capacity of their rig is going to be tested, like it was for Hal Roth who consistently dragged an anchor in Patagonia that seemed bullet proof everywhere else, finally heaving up on shore and almost losing everything.* That's why advice like "just get a bigger anchor" is generally good, until the anchor isn't big enough.* Some people love Danforth types (I carry an FX-85 as a backup), but also recognize that when they get a rock between the shank and the fluke they are useless, which is why some heretics refer to them as not "general purpose".* There are no situations where a Bruce, Delta, CQR, Spade, etc. can be incapcitated by a 3/4" pebble, but that is not the case with a Danforth.

The whole concept of tandem anchoring is that when your "really big" anchor you use day in and day out just might not be enough, you can trail an anchor and if you do it right, increase the holding power of the ground tackle significantly.* If you do it wrong, you can decrease it, but since it is a technigue recommended by some experienced cruisers like Earl Hinz and many, many others, I'm not sure what the basis for rejecting it as a strategy would be, especially if your only experience is based on doing it incorrectly, as appears to be the case with Mssr. Poiarud.*

What the concept is not is a way to make a bad primary anchor into a good one, so I am not sure you'll find data on that one, Egregious.

 

[Egregious]

Well said, Delfin.

The thread is about using two anchors in tandem, not about using one big ass anchor.

Someday I might be in a blow and I'll need to use this technique.* I will continue to monitor.

 

[Marin]

Some anchors like the Rocna incorporate an attach point in the shank specifically for the attachment of a tandem anchor out in front of it. The use of tandem anchors seems to be a popular technique among boaters, particularly sailboaters, who operate in areas with large, open anchorages that can be subject to strong winds and big waves or swells. Almost all the posts or articles I've read over the years about using tandem anchors have been from people who boat in the southwestern Pacific. As I understand it from what I've read by people who use this technique regularly, the primary purpose is to help the main anchor remain set in conditions that could cause it to come out or drag.*

The technique seems to be used in situations where there is no viable option to up-anchor and go somewhere else because the conditions are such that trying to go somewhere else poses more risk than staying put and riding it out for a day or three.* So the object becomes to stay anchored and not drag even when conditions get really severe.

I have never seen the tandem anchor technique described as anything other than a severe-condition tactic in pretty specific waters.* I've never seen it described as something one would do in "normal" boating in places like the PNW, ICW, inside waters of SE Alaska, etc.* So even though our anchor has a purpose-designed accomodation for tandem anchoring, I doubt in the kind of boating we do we will ever need or use this technique and we do not carry the hardware necessary to use it.


-- Edited by Marin on Wednesday 30th of June 2010 11:29:33 PM

 

[FF]

Tandem anchoring does work , but I think it would best be used on a boat that carried insufficient ground tackle and was warned of an impending big storm.

Proper storm anchoring (and other great ideas for an offshore boat) can be found in ,


Oceanography and Seamanship by William G. Van Dorn. 453 pages. Cornell Maritime Press; 2 Sub edition (February 1993) Illustrations by Richard Van Dorn ...

Free at the library.

 

[skipperdude]

Delfin,

*I was under the beliefe that a Bahamian moor was two anchors set 180 deg apart.*

but both anchors coming off the bow roller as compared to one bow and*one stern anchor. If both are set off the bow the boat can swing 360deg.
As most boats need to swing with windage and current.

to set it you drop anchor and let her drift until you get 2x the scope drop the second anchor and haul in on the first untill the rodes are equal with the boat in the middle. wala, the Bahamian moor.

A bow and stern anchorage locks the boat in a straight line. Not advisable with a boat with high windage or a keel. They seem to like swinging bow into the wind.

Another idea a little easyer to set is a forked moor . Set one anchor, drive forward and*to the left or right **drop the second anchor back off to scope to give about a 60 deg angle between anchors. ideally both anchors should share the load equally.

When you think about it In bad weather it can be downright indispensable to have a second set of ground tackle prepared in case the first one drags or breaks.

SD

 

[Delfin]

Skipper, I have seen the forked mooring you refer to also called a Bahamian moor, although I am not sure the terminology is that precise.* The 180 degree set is not uncommon in crowded anchorages (in the Bahamas for example) because it limits swing.* The 90 degree set is frequently recommended in storm conditions, although I don't like that too much because of the uneven loading on the rodes, which can result in one anchor dragging, then the other, and the virtual guarantee of getting them tangled when the wind veers 180 degrees, like it does in hurricanes.*

We're hopefully going to be able to head down to Patagonia, then west* to NZ and OZ in three years or so, and our approach to anchoring in Williwaw territory in remote areas is what I have been considering.* I've dragged anchor off Lahaina (Bruce 44 in sand, 12 ton sailboat) and in Hospital bay on the east side of Vancouver Island (same boat, CQR 35# in mud), and I would rather not do so again.

The approach we'll be using on Delfin is:

1. Big primary.* Right now a 176# Bruce, but I am considering the 140# Rocna because it shows so well in all the tests.* No one tests a 176# Bruce, and I suspect the sheer weight of the thing will cause it to set most always, and once set I do not think there is a better anchor than a Bruce.* It's getting the lighter ones set that is the trick.
2. Lots of heavy chain.* We have 400' of 1/2" G4, although if I win the lottery I'll change that to 1/2" G7.
3. If we switch to a Rocna, a setup for tandem anchoring with a FX 37 Fortress trailing off 50' of 3/8" G7 behind the primary for use in dicey situations.
4. 50' of 3/4 nylon snup line
5. Secondary chain/rope combination with a Fortress FX 85.
6. Tertiary chain/rope combination with a 50# Danforth.
7. Stern chain/rope with a 25# Rocna.

Given Murphy's law, I'll get all this set, and as the winds pick up, a 65' Bayline will drag its 35# CQR into me and we'll all end up on the beach.....

 

[Nomad Willy]

Delfin,I'm glad you started this thread even though TA has many roads to failure and has little practicality it's a bit like thinking out of the box. The discussion has given me an idea for my anchor that frequently won't set. A small 2# bruce trailing 2' behind my XYZ anchor may stabilize it enough so it would set dependably. I've got the little Bruce as a shore hook for my skiff while beached.
If I was to TA to increase holding power I'd deploy the first anchor that had the least short scope ability and then 50 to 100' downwind deploy the 2nd anchor. Then set for max scope.This would be fairly dependent on a fixed wind direction of course but each anchor would*be properly set and could be reset. Most boaters wouldn't need to get a BA in ground tackle and it's use and most trawlers have a 2nd rode available.
I'm intrigued by the fact that Peter S declared the lower hole as the TA attach point. I was assuming that hole would be best for retrieval. I wonder what the reason is for the upper hole being better than the lower location for retrieval? The same spot is chosen on the Manson as well.
Delfin,
Here is a boat that was in Thorne Bay in the recent past that appears much like yours.

 

[skipperdude]

Wow!!
Dude, you are the Anchor man.

If I never drag anchor again it will be to soon.

Only happened once To me and it wasn't even my boat.
I have to say I didn't set the anchor. familarity breeds complaciency. The skipper had anchored many times in the same spot. Just wasn't expecting gail force winds.

That was fun.

SD

 

[Delfin]

Nomad, like you I was interested in Smith's discussion of hole placement for attachment.* Once I read it, it made perfect sense that if you tug on a Bruce, or a CQR, etc. at the top of the shank, you'll tend to pull the plane of the flukes more to vertical resulting in a pop out.* Attaching to the lower hole shouldn't cause that problem, so that basically means that you couldn't attach a tandem to a Bruce, CQR, Danforth, etc. because they don't have the right place to make the attachment.* The Manson is just a Rocna knock off, so it would work, like the Rocna.

I think you've got the right sequence on how to deploy, but I don't think you want to try to set the tandem before the primary.* I think I agree with Smith that the tandem should just be laid on the bottom, then lower the primary and set it.* If the tandem just lies there doing nothing, great, you didn't need it.* If the primary starts dragging, then you have a shot at slowing down the drag and holding as the tandem digs in, which it certainly should given the infinity :1 scope it has relative to the primary.* Again, we are talking about theoretics that only apply in really bad situations, but that is the time I find I need a thought out plan already in mind because my brain doesn't work at those times.

I don't think I've seen that boat.* Kind of looks like a Malahide that has had the P/H remodeled.* If you get a chance, perhaps you can i.d. her for me.

 

[Delfin]

Skipper, I only have two mottos when it comes to boating:

1.* Panic early and avoid the rush.
2.* If it's not worth over-doing, its not worth doing.

 

[skipperdude]

Right on dude.
My signature is another.
Ya gotta be able to fix it.

 

[Marin]

nomadwilly wrote:


The discussion has given me an idea for my anchor that frequently won't set. A small 2# bruce trailing 2' behind my XYZ anchor may stabilize it enough so it would set dependably.

Eric--- A question.* For some time you have been talking about the difficulty of getting your XYZ anchor to set.* Now you're talking about using a tandem setup to try and stabilize the XYZ so it will set.

So---- why not give up on the XYZ, which seems to be less reliable that you'd hoped, forget about time consuming and hardware-dependent solutions to try and make it set, and simply switch to an anchor that DOES set, no tandem helper anchor or other*assist method*needed?

Just curious......

 

[Capn Chuck]

Just for clarification, a Bahamian mooring is when the anchors are set fore and aft for shifts in the current and or wind. Two anchors off the bow at angles is not a Bahamian Mooring. Chuck

 

[skipperdude]

Right, it's called a forked moor.

2 anchors off the bow at 180 Deg is a Bahamian moor. The Bahamian moor entails two anchors both set from the bow, one up current the other down current,180 deg apart. The vessel pulls on either or both anchor rodes, and is immobilized within a tight radius regardless of wind direction or current flow.

Two anchors set one fore and one aft is called a fore and aft moor.
SD

 

[Nomad Willy]

Marin,I did. Remember you talked me into buying a new anchor and I got the Manson? Well the XYZ is mostly a toy now. Gotta figure it out. When I've tried to set it it always feels like it's bouncing along the bottom and I think my theories of the past have been wrong. I now think the XYZ has been tripping on it's nose like a plane landing w out a nose wheel (nose into the runway and tail up and over) but i think the XYZ never does the 180 flip. The water stops it and it just tries to set again nosing in again and over and over unless it's mud. If my new theory is right the little bruce will set and drag. Bruces are good at that * *..right. The drag will keep the tail down and serious penetration should result.
I put the bolts in the slot on the MS but haven't used it yet. I got together the trip line w a little orange float but don't know how to inflate the float.


Eric

 

[Marin]

Eric---* We use a white crab pot buoy on our trip line.* To make it easier to retrieve I put a section of 1/2" (ID) PVC pipe through it.* The long end sticks up and the short end has a couple of shaft zincs on it so the buoy floats upright.* Just last weekend I modified it by installing male and female threaded ends just above the buoy so I can unscrew the long end which makes tthe whole thing much easier to stow.

The photo shows the original version.* The current one sticks up twice as high so I can grab it from the deck without the need of a boathook.* The vertical pole also makes it easier for other boaters to see.

-- Edited by Marin on Thursday 1st of July 2010 11:14:00 PM

 

[FF]

to set it you drop anchor and let her drift until you get 2x the scope drop the second anchor and haul in on the first untill the rodes are equal with the boat in the middle. wala, the Bahamian moor.

This is perhaps what is needed for open and deep water.

Usually the Bahama Moore is used to secure a boat in shallow water , inside a restricted swing area (mooring field) or in a really crowded harbor.

The technique then is to pull yo abeam the stern of the boat in front , drop the fwd anchor , with location ball , and fall back to set the anchor.

We simply lower the stern anchor off the transom and walk the rode to the bow . In 10 ft of water (sometimes only 5 ft) the scope is fine for a Danforth , and a good pull will let you know if its set well. The "lookey pail" will let you get a visual on both .

Departing the stern anchor is pulled first , no big deal its a 20lb anchor most evenings, and the stern is straight over it.

Necessary for packed conditions in shallow water , but the system does work to about 20 ft of depth , if extra stern line is passed , after the initial setting pull.

 

[Nomad Willy]

Marin,OK good. Mine's going to be orange, a soft fender like rubber/plastic ball. Should be really easy to snach w a boat hook. I'm not going to store the Manson in the anchor rode box like I'd planned. When it gets really rough the rode box tries to get away. An extra 18lbs would tip the situation toward the get away side. But then there will be plenty of room for the sacrificial end of the rode AND the trip line. If I find the trip line to be a lot of trouble, and I don't expect that, I'll open up the slot and see how many anchors I'd have to buy. I wonder if the roll bar diameter is different on the Rocna. The big difference between the Manson and the Rocna is not only the shank but perhaps more importantly the up and down elevator part of the TE. Some anchors rely mostly on the UE feature for holding like the Spade and the Delta. The Manson does'nt have it (another reason I didn't buy it) but Rocna has both roll bar & UE and according to the tests I read the Manson does'nt lack performance for lacking the UE feature either so I'm thinking the roll bar does most of the holding work where employed. The SARCA had a larger roll bar but of smaller dia.


Eric


Marin * * * .. your dinghy's on your boat * *.. while you took the pic * *..hmmmmm?


-- Edited by nomadwilly on Friday 2nd of July 2010 11:30:37 AM

 

[Marin]

Eric--- While I think your theory of the action of an*up or down curve at the rear of the fluke of an anchor like the Rocna, Sarca, Manson, etc is correct, I think the reality of this curve's effect on the anchor's performance is very minor. The basic principle of the roll-bar spade anchor--- it ends up on its side, pulling on it pivots the sharp point into the bottom and the blade slices down, and the blade then rotates to end up resisting the boat's pull because of it's basic shape and angle into the bottom---- is why they work.

So in my opinion, the angle of bend at the very back of the fluke, either up or down or none, is pretty irrelevant to the anchor's actual performance.

Much more important, I think, is the shape of the tip, which has to do the initial penetrating, and how the design enhances the pivoting force that drives the tip into the bottom. This is where I believe the Rocna's design is superior to the Manson Supreme's.* If there is any difference in the diameters of the roll bars on the Rocna, Manson, and Sarca, it's probably not much and I doubt it makes any difference.* There is a small hole drilled in the top of the Rocna's roll bar and I thought it might be of some significance--- when I asked Rocna about it they said it's only*there to aid in draining the galvanizing material when the anchor is manufactured or re-galvanized.* So, nothing dramatic

As to the photo, we carry two dinghies on our our boat. It came with the lovely Montgomery sailing/rowing dinghy in the cradle on the aft cabin top. It's a great little boat, a lot of*fun to sail or*row,*but as a utilitarian shoreboat, not so good. Too tippy, too small.* So a few months after acquiring the GB we added a 9' Livingston on Weaver Davits on the swimstep (see photo below).* We deploy and retrieve it using the boom fall--- a one person, one hand, very fast*operation. *I took the buoy photo from Livingston.

-- Edited by Marin on Friday 2nd of July 2010 12:07:18 PM

 

[Nomad Willy]

Marin,Good dinghy trick. I may have the same dinghy on the Willy. I'll check. It has a plaque on the transom and I know it's a sail boat. I glassed over the CB trunk some time ago. But it may not be the same boat as I don't consider mine a good rowboat. It requires concentration to keep it on a straight course. But it is fast and performs well (7 or 8 knots) w a 6hp Johnson at half throttle. I hate them but I bought a rubber duckie fron West Marine a few days ago * * ..51lbs. I can easily lift that op on my cabin top.
I agree w you. The trailing edge difference is that w the Rocna the trailing edge is part of the fluke area providing resistance/holding power whereas the trailing edge (as in elevator down) like the XYZ does not help the performance. But like you say the trailing edge probably is'nt a big factor in performance. And about the tip * * .. I agree w you again. AND I think the Rocna's tip is better. But as long as the Manson sets good I'll be happy.


Eric

 

[Marin]

Eric---

I've seen a lot of comments about the Manson Supreme over the years on forums like T&T. With the exception of complaints about the slot permitting the anchor to be pulled out of the bottom if the boat got off at the wrong angle to the anchor--- an issue they all solved by securing the rode to the hole in the end of the shank below the slot--- my overall impression of users' opinions of the Manson is that they were very pleased with its performance. So my guess is that you will be, too.

The first photo is one I took of our friends from France who boated with us last fall. This is the Montgomery Model 7-11 sailing dinghy we carry in the cradle on top of our aft cabin. It is fiberglass and teak and the mast (carbon-fiber I think) steps right up at the bow. Our friends are not large people, so the Montgomery worked out fine for the both of them. My wife and I, however, are not so small, so it's a one-person boat for us.

The second photo is what I believe is the ideal dinghy of all time. Easy to build, easy to fix, and if you get tired of it you can throw it in the dumpster with no regrets. I took this shot the other year in Xiamen, China, and it's actually a "skiff" that a local fisherman uses to get out to his moored fishing boat. The fishing boat isn't much more sophisticated or better built--- it's just bigger and has a motor of sorts. But you could build something like this real easy, although I don't think it would compliment the lines of your Willard very well.

The third photo has nothing to do with any of this, it's just a nice shot I took from the window of the house we rented up north on Vancouver Island when we went halibut fishing a few weeks ago. This is my idea of a room with a view.....

 

[Codger2]

Marin: That third photo is a doozy! It coincides with my mental image of what a great cruise should be. What a backdrop for a boat ride!

 

[Marin]

The boat in the sunset photo is a commercial fishboat based (I assume) in Port McNeil which is a few miles up Weynton Passage in the direction the boat is going. The boat is actually passing through the "junction" of Weynton Passage and the top of the infamous Johnstone Strait.

I put a Photobucket slide show together of shots from our halibut trip this year--- I will PM you the link if you'd like to see it.