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Old 07-25-2016, 07:08 AM   #221
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I hadn't really paid much attention to the "tandem" idea, even though I'd heard a bit about it over the years. Did have to do a modified Bahamian once, years ago, odd circumstances... I couldn't that it worked any better than a single anchor, and it took some work.


Having read over the last few references here.... I'm beginning to better appreciate that "Hammerlock" thing mentioned in the "Anchoring 201" ref.


I think if I were to have to do that, I could, relatively easily, deploy our FX-37, back down and set that properly... then move the boat back up that rode and deploy the SuperMax 17 in the same line as we used to set the Fortress (using track on plotter?), back down and set that properly but on slightly shorter scope.


Both anchors are properly sized for our boat: Fortress actually one size larger than maker recommendation, and the Max size also appropriate as a storm anchor.


Still thinking about it, though. Seems like high potential for fouling rodes, if the boat does any 360s. Just attaching the Fortress via the Max trip-line hole -- in an actual tandem rig -- would maybe better deal with that fouling potential...


-Chris
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Old 07-25-2016, 07:52 AM   #222
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I think the hammer lock is only when your boat is sailing back and forth on an already tight rode.

It is not much more than using it as dead weight to slow the zig zagging. It you actually tried to set it on a short scope in bad conditions it would probably pull out anyway. And if set on a longer scope, might as well just set 2 anchors at 60 to 90 degrees normally.
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Old 07-25-2016, 09:10 AM   #223
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I think the hammer lock is only when your boat is sailing back and forth on an already tight rode.

It is not much more than using it as dead weight to slow the zig zagging. It you actually tried to set it on a short scope in bad conditions it would probably pull out anyway. And if set on a longer scope, might as well just set 2 anchors at 60 to 90 degrees normally.

Ah. Hadn't realized it was mostly about that. Thanks.

With no keel to speak of, we do tend to sail a bit under some conditions...

-Chris
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Old 07-25-2016, 09:54 AM   #224
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Steve Bedford wrote;
"Remember, if one anchor gives way, you are on that one remaining anchor. If it is undersized, you may have a serious issue."

Steve it's kinda like the twin engine question. When my 40hp engine fails I'd rather have a 5hp engine to take over powering the boat. When the 40hp engine quit I'd consider a spare 5hp a blessing .. not an issue. And if I had a secondary anchor it would be much like (but not like) the secondary engine. The anchor question is less black and white but in most situations it would be preferable to have a small anchor dragging than nothing.

But if the holding power of the secondary anchor was far less than the primary ... why bother? As I always say use one big anchor instead of two small ones for better results. But reducing the shock loads w two anchors may increase the probablity of one anchor being always set or dragging slowly while the other resets.

So as I see it tandam anchoring has three advantages:

1. The ability to deploy much more holding power when you're deploying anchors by hand. Two 20lb anchors set well is better than one 20lb anchor. And deploying a 40lb anchor may be too difficult physically. This obviously dos'nt have wide appeal here as most on TF have a winch.

2. Absorbing shock loads that may cause a breakout. There are several different riggs that reduce the shock loads and likely would arrest a breakout. So a secondary anchor can not only add holding power but can act as a Big Kellet hugely reducing shock loads and increasing catenary.

3. As earlier presented in post # a trailing anchor like a small Fortress could keep a big Bruce down in the seafloor by not permitting the back end of the Bruce to pop up and out .. Like it does as evidenced by Steve's (Panope) tests. The Bruce/Claw could possibly go from a questionable anchor to a top performer. I'd like to see a test of this. A lot of skippers could add a tag Fortress to another anchor greatly increasing it's performance. Kinda like a farmer pushing down on the plow handles to keep the plow business end in the ground.
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Old 07-25-2016, 10:07 AM   #225
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My understanding of tandem anchoring depends on forces acting simultsneously on the 2 buried snchors.

If not, none of it is remotely predictable and as soon as on breaks free you are really only depending on the other anchor...and that cycle continues. Especially if the setup at ALL causes on anchor to lessen the others ability to stay put.
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Old 07-25-2016, 01:37 PM   #226
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Now after posting and thinking I like Ptitug's post #201.

I'm wondering if it will work better closser hauled .. say 2-3'. With a Claw the trip line attach hole is at the top of the anchor where tension woul tend to hold the Back of the Claw down. With the business end held down it can't help but hold. So if I said anything critical about Ptitug's system I take it back. But now I'm thinking it could interfere w the main anchor setting. Probably would'nt help the Rocna any w it's trip line low. May insure it will stay upside down. Hmmmm
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Old 07-25-2016, 02:48 PM   #227
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But if the holding power of the secondary anchor was far less than the primary ... why bother? As I always say use one big anchor instead of two small ones for better results. But reducing the shock loads w two anchors may increase the probablity of one anchor being always set or dragging slowly while the other resets.

So as I see it tandam anchoring has three advantages:

1. The ability to deploy much more holding power when you're deploying anchors by hand. Two 20lb anchors set well is better than one 20lb anchor. And deploying a 40lb anchor may be too difficult physically. This obviously dos'nt have wide appeal here as most on TF have a winch.

Just to keep stirring this pot...

There's a third option: two BIG anchors.

The point about being able to manually lift an anchor of X weight is I think important... even for those of us with powered windlasses... as in cases where the lift mechanism maybe craps out.

But aside from that, or maybe "within those dead-lift limits," I doubt I'd get all that enthused -- especially given the extra work involved -- about two small anchors, or one large and one small anchor, deployed in tandem.

I reckon if I need extra holding power, and it's gonna take some work to get there from here... I'd just as soon get a as much extra holing power as possible from that second anchor. Which suggest BIG. (At least within the same dead-lift limits that are already impacting my choice of primary.)

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Old 07-25-2016, 05:50 PM   #228
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Ranger,
Yes of course big is good and for years I've supported combining the two anchor weights and get one big anchor.
But in certian circumstances the tandem makes sense to me. Especially the Ptitug rig w the smaller Fortress.
The well known two anchors w their own rodes system looks troublesome and vulnerable to me. Tangled rodes is not something I'd want to deal with.
Personally I'm betting on a modified anchor w better penetration for better performance from a 15lb anchor.
A combination of two anchors w a different stack up of strong and weak points could possibly work together better than singularly. And Ptitug seems to have a system that would be one to adopt or one to try as a jumping off point to something even better. A fortress for example, w it's extreme holding power coupled w an anchor that has ultra dependable setting ability (perhaps a Claw) may make a great combination. Pick and choose.
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Old 07-25-2016, 06:53 PM   #229
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I think that was my point Eric. If they have never fouled in all that time, when in the normal course of events, one anchor would have to be being dragged past the other as they re-set after a current/tide/significant wind shift, and during which you would surely expect the Rocna to pick up the line to the Fortress across its fluke once in a while at least, does sort of beg the question...is the Rocna, the second anchor, and therefore the one that would have to be dragged past the Fortress in that re-set, ever in fact doing so..?

Or, is it staying set, twisting round, or breaking out but re-setting so quickly it is in effect rendering the Fortress at the end of the connecting line, basically redundant..? One would never know. You can't see. But never fouling one on the other in all those years might be the only evidence that might be the case.

My respectful suggestion therefore to PgiTug, is to just leave the Fortress off a few times and see how that goes. What's to lose..? Psneeld does that all the time. Marin also. In fact everyone else that uses a Rocna I know of does just that. He may be going to that extra effort for nothing, even if he has it down to a fine art. Just sayin'



Peter,
Finally getting back to this.

Yes the Fortress may be a waste of time. Would be a waste of time if it never dragged. And if it's that big and well deployed the Fortress is just extra baggage. Also the Rocna has it's tandem anchor or trip line hole very low on the Shank so the front end of the rode to the Fortress may impede penetration of the Rocna because the short rode would need to be dragged down through the bottom to fully set the Rocna. The drag on that short rode would tend to hold up the back of the Rocna.

But you're right ... if there's no advantage why do it? But how are you going to know that? I anchored in 50 knot gales twice, once w a 13lb anchor and once w an 18lb anchor. Would I have been better off w a tag anchor or a bigger anchor? Obviously not as we didn't drag.
I see the tandem anchoring as a good way to extend the conditions and/or bottom types that one's "gear" can successfully operate in. One can have a Fortress and operate in rocky bottoms or have a Rocna and operate in mud. You having a Super Sarca probably wouldn't benefit (or not very much) from a tandem arrangement since the SS operates gracefully and dependably on essentially all bottoms.

My respectful suggestion therefore to PgiTug, is to just leave the Fortress off a few times and see how that goes. What's to lose..? Psneeld does that all the time. Marin also. In fact everyone else that uses a Rocna I know of does just that. He may be going to that extra effort for nothing, even if he has it down to a fine art. Just say'in'[/QUOTE]
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Old 07-25-2016, 07:52 PM   #230
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I have a 60 pound Manson Supreme....
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Old 07-25-2016, 10:54 PM   #231
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PeterB,
Perhaps the Rocna just has'nt dragged. They are after all a very good anchor.
Exactly...that was my entire point Eric. Quite possibly allowing PgiTug to think his tandem system was working fine, when actually the Rocna was rendering the Fortress redundant anyway.
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Old 07-25-2016, 11:31 PM   #232
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The 2 anchor set up seems to me to present the complexity of a triple backwards somersault Olympic Games dive, with pike. IMO, better off selecting a good multipurpose anchor, or 2 if you prefer to select anchor design based on the bottom type, and go with that.
But if you find you can routinely anchor using a 2 anchor set up,and you can make it work without arguments between the 2 anchors and rodes, it works for you so go with it. Anchoring is something of a black art, if anchor whispering works, that`s your method, have faith in it.
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Old 07-26-2016, 02:16 AM   #233
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I have a 60 pound Manson Supreme....
Sorry, but same difference essentially...
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Old 07-26-2016, 06:22 AM   #234
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I have a 60 pound Manson Supreme....
You're younger and stronger than I am. I chose to stop at the 50-lb MAX.





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The 2 anchor set up seems to me to present the complexity of a triple backwards somersault Olympic Games dive, with pike.

Sounds about right, to me.

After more thought, I suspect I could deploy and set our Fortress with some slightly different rode connections than our normal... then move back up that rode, remove part of that modified rode, and shackle the rest to our SuperMAX at a useful distance... then deploy and set the MAX in the same line...

Both of our anchors are (said to be) suitable for storm conditions for our boat.

Would I need to or want to do this routinely? Absolutely not. Would I want to do this occasionally, if heavy weather threatens? Wouldn't be my first choice; I still like my existing hurricane plan. But then I usually have the luxury (?) of working that kind of plan.

So I think what I could do -- with tandems and modified rodes and setting two anchors and all that -- isn't really high on my list of what I would do.

Mostly due to that complexity thing.

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Old 07-26-2016, 08:39 AM   #235
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"Steve it's kinda like the twin engine question. When my 40hp engine fails I'd rather have a 5hp engine to take over powering the boat. When the 40hp engine quit I'd consider a spare 5hp a blessing .. not an issue."

Sorry, I have a different opinion. You would never use your 40hp and your 5hp together. Having a 5lb anchor as a back up to your primary anchor is quite different than using them in tandem. If the 40lb breaks free in the middle of the night, you of course can not expect the 5lb to hold.

"But if the holding power of the secondary anchor was far less than the primary ... why bother? As I always say use one big anchor instead of two small ones for better results."

Agree.

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Old 07-26-2016, 09:22 AM   #236
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I have referenced Bob Taylor in past discussions for his extensive scientific anchoring knowledge that he acquired during 45+ years with the US Navy and offshore industry.

Our late company founder kept a small library of his US Navy work and here's a download to a report that Bob did on multiple anchor use:

https://www.dropbox.com/s/cpyumsguo6...83-05.pdf?dl=0


On page 4 ( image below) of this report is a brief summary of different anchoring set ups. When I questioned him recently on using our anchor in a tandem (or piggyback) combination, his comment was:

"The best way to use Fortress and most other anchors with this configuration in tandem is to use option 4 in table 2 of the Tech data Sheet. This allows each anchor to function properly. In reality the rear-most anchor will eventually move into the trough created by the front anchor and dig deeper than it normally could resulting in more than twice single anchor capacity."

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Old 07-26-2016, 03:44 PM   #237
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I
"The best way to use Fortress and most other anchors with this configuration in tandem is to use option 4 in table 2 of the Tech data Sheet. This allows each anchor to function properly. In reality the rear-most anchor will eventually move into the trough created by the front anchor and dig deeper than it normally could resulting in more than twice single anchor capacity."


How would one actually deploy that (option 4) set-up? Shackle the two anchors (anchor chains) to the main rode, dump it all overboard, back down?

If one anchor sets first (which might it be?), how would one get the other to set? How would one know that had been accomplished?

-Chris
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Old 07-26-2016, 03:55 PM   #238
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I think this is a narrow variation of a Bahamian mooring where each anchor is on its own rode. I will check to make sure.

I found this animated Gif for setting two anchors on a sailing site awhile back.


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Old 07-26-2016, 07:38 PM   #239
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But if the wind even changes 20 degrees the load is almost all on one anchor.

One anchor 20% bigger would be better.

Love your graphics Brian. Especially the propwash.
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Old 07-26-2016, 08:21 PM   #240
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I have a 60 pound Manson Supreme....
I have a 15lb Supreme. Well it was a Supreme.
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