Tandem Anchors - a Thought

[oldvarnish]

Originally Posted by DaveOnCudjoe

I had always assumed that practice was not advised since the holding power only multiplies if on a straight pull and in fact reduced on an angular pull. Dave

I think a properly set pair of tandem anchors would be a straight line pull, so the issue of an angular pull doesn't arise. Since one goes down very soon after the other, it's difficult to see how they could be much out of line.

[estarzinger]

Originally Posted by Dragon701

From our experience lines of 150' to 200' should be plenty for "regular" tying ashore. You may want more for other purposes. Ours currently are 280' and 400', which would have been sufficient in Patagonia.

My suggestion would be two 300' lines, as that gives you the ability to get the lines ashore and tied in before you are too close. In Chile the lines don't need to be too big or strong because if you do it properly at the end you are tucked right into shore and the wind shoots over the top of you and the lines don't get so much load. For Chile I would also endorse floating lines (polypro or spectra) because they are much easier to dinghy ashore and don't bring back so much kelp. We got our lines from a fishing chandlery in cork (Ireland) . . . cheap and surprisingly high quality/durable.

For our third transit, when we planned (and did) to winter in the beagle we added a 600' spectra line so we could reach way out to a 3 point secure tie.

In S Georgia and Antarctic it's a little different, because the shore line does not offer the same amount of protection (so the lines need to be stronger) and there can be pretty big ice floating around which floating line will trap (so I prefer sinking nylon line for those places)

We now use heavy duty lifting straps for going around trees and rocks ashore. They have loops to which we connect with a large shackle. They are much easier to use than the chain lengths that we dragged ashore in the past.

We started with straps but ended up just tying the shore line directly to the tree or boulder. We would tie a huge loop (another reason to have slightly longer lines) where the bowline was out over the water, so we could untie it from the dinghy without having to go ashore.

Spools are nice but we like extremely clean decks, so we had some mesh bags made up - tall and thin with a wire hoop sewn into the mouth. The line would come out tangle free and one person could stuff the line back in.

You will find people in the Beagle who have come down the channels who want to unload their lines, so it is possible to pick up a few extra and then turn around and resell them in puerto montt to someone starting out.


Another thing to mention is a kelp knife. There are all sorts of fancy solutions. We ended up with a stainless serrated bread knife on the end of a 10' carbon sail batten. In a few Anchorage's you will pick up a huge ball of kelp on your chain and need to cut it off as you crank the chain up.

The Fisherman is a good thick kelp anchor. That's one situation where we found the Rocna to be not so good. It was ok in Chile, but in South Georgia we had trouble with it in the really heavy kelp. I think the kelp drag on the roll bar prevents it from digging in. The Manson Ray worked better in those situations.


Dragon, any plans to go back there? It's one place we hanker to get back to, but it is a long way to get there from anywhere.

[Dragon701]

No plans currently afoot.

We just finished a year with our kids on (I hesitate to say it given the current controversies about Anna) an Atlantic 55 -- Nova Scotia, Bermuda, Virgins, Columbia, Panama, Honduras, Guatemala, Belize, Mexico, Bahamas and home to the Cape Cod area. Spectacular experience (and a really great boat for us).

When the kids are off to their lives, we might head north again. In 1984, on our way back home from Spitzbergen via Jan Mayen and Iceland, we tried to go to Greenland (Angmagssalik). It was late in the year and we got fouled up with ice while crossing the Denmark Strait, doubled back to Iceland, the Faroes, Scotland and Ireland; left the boat for the winter; and came home through the Azores and Bermuda the next summer. Long story ... but I have always wanted to sail to Greenland (we subsequently flew a small plane to Angmagssalik -- off topic).

On the other hand, my old bones really like turqouise waters and balmy beaches.

[estarzinger]

"we tried to go to Greenland (Angmagssalik)"

East coast Greenland! Very brave! We know people who have sat in Iceland for a couple seasons waiting for a clear shot at Angmagssalik. I think we only know two people who have made it in. . . one with the help of an icebreaker.

"We just finished a year . . . an Atlantic 55 . . . great boat for us."

I will not distract this thread . . . but you want to add any thoughts on the Anna thread about when you reefed/how you managed the sail plan/how careful (or not) you felt you needed to be with the boat? I am honestly curious about this. Also would you take that boat 'to the ice'?

"On the other hand, my old bones really like turqouise waters and balmy beaches."

Yes, I hear you, but I have convinced myself that's just laziness setting in and when I get off my butt and get south again it will be wonderful again.

Perhaps by then, we will have 'the next next new thing' in anchors to test and debate

[estarzinger]

Originally Posted by Dragon701

Spitzbergen .

Go soon, getting crowded! 80 sailing yachts checked in with Svalbard port authority this year . . . and 4 boats 'crowded' into Hornsund anchorage

[Kettlewell]

Back to tandem anchors. To me they make no sense. Why put two anchors on one line, therefore increasing the difficulty of both setting and retrieving the mess? Plus, you lose the redundancy of having two separate anchors down on their own rodes. I doubt you will travel around with the two anchors on one rode most of the time, and then you have to rig this mess when things are starting to look ugly. I have numerous times been at anchor only to experience sudden wind increases beyond what I felt comfortable with. My first response, given the room, is to let out more rode and then either drop a second anchor from the boat or take one out in a dinghy. This type of situation can happen anywhere, not only in Patagonia, though I will admit the conditions there can be pretty extreme. Our worst blow short of a hurricane was in the Chesapeake when we were hit with what was apparently a tornado while at anchor. The main anchor left us dragging at a high rate of speed, but a second anchor stopped us. We were unable to measure the wind accurately ourselves, but the nearby Still Pond CG station reported 88 knots I believe. I had to set the second anchor with my eyes closed due to the firehose like rain driving in my face. Since then I keep a diving mask handy to the cockpit.

[Kettlewell]

By the way, if you are interested in tandem anchoring check out the Rocna folks Web site for a really good page on the subject. Not my thing, but it sounds like they have thought it out well.

One point is that everyone seems to assume that if you use two anchors they have to be set in a wide V. That is not the case. As long as you use non-fouling types, you can set a very narrow V and on slightly different scopes, which eliminates the problem of what happens when the wind shifts and the boat swings.

[oldvarnish]

I was just about to post the same link to the Rocna anchor's designer's website.
His view is that there's no need for a second anchor if your first one is big enough. Makes sense.
It's worth a read.

[gettinthere]

kettle

you can go both ways. if a big storm is anticipated, rig the tandem anchor. If a sudden burst hits, you can do as you did. As they say, It's all good.

[Kettlewell]

I just don't see the tandem rig working as well as two anchors in most big blows. Most of the time a big blow is caused by a passing thunderstorm, a frontal system, or a tropical storm, and they all mean the wind will be shifting around a lot. I don't see how the tandem will cope with a 180-degree change in direction, or even less. Eventually you won't have two anchors in a row, and then I don't see the furthest anchor helping all that much. If the wind goes 180, you might have the problem of your rode fouling on one of the anchors. Whereas, two anchors, set in their own patches of bottom, with their own rodes, will continue to work as the wind clocks around, with some need for adjustment depending on how you have them set. Plus, I still think it is harder to deal with the tandem rig than two separate rigs, both setting and retrieving.

[estarzinger]

Originally Posted by Kettlewell

I don't see how the tandem will cope with a 180-degree change in direction, or even less.

The OP was asking about tandems in Chile/patagonia. There you are mostly (95%) anchored stern into a tiny cove with shore lines. You are not swinging. Tandems have proven to work quite well in that particular situation. And strong winds are common enough, that those with too small main anchors just permenantly rig the tandom and drop it every day while they are in chile.

Chile is the only place (I am aware of) where there is such a body of evidence about tandoms. So, for other places/situations we just end up with a theoretical debate, and we all know how useful and productive those are about anchors

[Kettlewell]

I will grant I have no experience in Chile. It sounds like a pretty unusual situation. Why is it that you end up tied up/anchored like that, and the wind doesn't switch around?

[mrohr]

Don't knowabout chile and have only anchored in thick kelp once (fisherman worked) but agree with others that tandem seems like unnecessary complication with retrival and deployment. One big anchor with exrta rode ( my setup allows extra chain to be added if it blows up without pulling the anchor off the bottom). I have and will use a second anchor with its own rode at an angle to the first if big things are comming and this has worked well. With a tandem setup ,if the first anchor drags the second will have to set in the furrow dug by the first; maybe this is an advantage since the dragging anchor might be clearing a path for the second anchor to get thru the kelp and into the bottom,there must be some holy mess when, and if, you can get it all back on deck.

[estarzinger]

Originally Posted by Kettlewell

I will grant I have no experience in Chile. It sounds like a pretty unusual situation. Why is it that you end up tied up/anchored like that, and the wind doesn't switch around?

The strong winds (during the summer) are all westerly (NW or SW).

The strong winds down there are very strong, and the anchoring routine is designed to bring you in close to shore so that the winds goes right over you rather than hit you.

The shore line has been closely examined by a several generations of cruisers for 'the perfect cove', which has steep side walls, is about 3 boats wide, has about 15' depth 20' from shore, and has decent size trees at its head (to tie to but also means that the winds are not so strong there).

There is one of these coves about every 5-10 miles along the channels. Once you get the technique down (its very much like med-mooring), it provides an absolutely bulletproof tie-up and you can sit and watch hurricane force williwaws hit the water 50' in front of your bow while there is almost no wind on your boat.

Once you get used to it, you don't want to go back to the regular way of anchoring.

Back to tandems . . . I think (almost) everyone agrees that one big anchor is preferable. The question is simply what to do when you have decided your main anchor is not big enough and you feel you need to put two anchors out - series or parallel . . . endlessly debated.

[Kettlewell]

The shore line has been closely examined by a several generations of cruisers for 'the perfect cove', which has steep side walls, is about 3 boats wide, has about 15' depth 20' from shore, and has decent size trees at its head (to tie to but also means that the winds are not so strong there).

Wow, fascinating! Of course I have read of people doing this, but I thought it was an occasional unusual situation. Thanks.