A Little Help in a Hard Chance
My Last Word on the Z‑Drag
By Tamia Nelson
March 23, 2010
When, back in November, I outlined some of the many uses for the prusik hitch, I had no idea the topic would prove as popular as it did. I guess I shouldn't have been surprised, though, because my article made mention of a much‑used contrivance for parting broached boats from the rocks that held them: the aptly named "Z‑Drag." This improvised tackle can be assembled at the water's edge from a long rope, some high‑breaking‑strength cord, and a couple of carabiners. Best of all, it yields a (theoretical) 3:1 mechanical advantage. And while my column wasn't intended as a primer on the use of the Z‑drag in salvage operations — that's a subject best learned from specialist publications and hands‑on instruction — the mere mention was enough to trigger a minor tsunami of reader mail. Those letters encouraged me to write a second article in answer to some of the questions raised by readers, and I thought that would be the end of it. But I was wrong again. The mail kept on coming. The result? A third article. And yes, this really is my last word on the subject.
Before getting down to business, however, I'd better recap the relevant bits of my first column. Not everyone has time to read through 2,000‑plus words, after all. That being the case, here's the meat of the matter:
Moving water exerts enormous force, and few paddlers are built like Arnold Schwarzenegger. So the Z‑drag is just the "force multiplier" we ordinary mortals need. In fact, bluewater sailors will note a close resemblance between the Z‑drag and the hauling tackle known as a "Spanish burton." Both offer a (theoretical) three‑for‑one mechanical advantage. That means you can shift a 300‑pound load with little more effort than it would take to move 100 pounds unaided, though the Z‑drag suffers somewhat in comparison with its maritime counterpart, since carabiners don't make very good pulleys. Still, even a little help goes a long way in a hard chance, and supplementary pulleys are available to improve the Z‑drag's performance.
I then offered this sketch by way of illustration:
And followed it up with a cautionary note:
Get the idea? Good. But don't assume that this sketch makes you an instant expert. I've left a lot of important details out of my schematic drawing, besides the rock that caused the problem in the first place: the second (or "brake") prusik that's often needed, for one thing, and the weighted bag placed so as to deflect the hauling rope's potentially lethal kickback if it should part while under strain, for another. These omissions are deliberate. You can't learn the techniques of whitewater rescue by looking at a picture. You have to practice them on the water, under the guidance of someone who knows the ropes. That said, a little reading can make the learning curve less steep. I recommend the Whitewater Rescue Manual, by Charles C. Walbridge and Wayne A. Sundmacher.
That was all I'd planned to say on the subject. I wanted to illustrate an application of the prusik hitch, and give interested readers some idea where to go from there. Nothing more. Some folks clearly got the message, as this letter from Tim Cashman illustrates:
Good article. I had seen flawed diagrams of a Z‑drag in several canoeing books. None of the other diagrams was a workable substitute for a block and tackle. This was the real thing.
But others didn't. Or they overlooked the caveats I'd scattered throughout my brief description. The subject of…
Was a particular sticking point for one reader, who wasn't satisfied with my cautionary note to the effect that "carabiners don't make very good pulleys." He went further, asserting that the frictional losses were so great as to render the exercise of setting up a Z‑drag without pulleys all but useless. I'm bound to say that this hasn't been my experience, but his comments warrant careful consideration nonetheless. No tackle ever yields anything like its theoretical mechanical advantage. According to my copy of The American Merchant Seaman's Manual (1942 edition), the Spanish burton — that's the standard 3:1 tackle I mentioned in my original article — loses nearly a quarter of its theoretical advantage to frictional forces. And the losses when a hauling line slides over one or more carabiners would be higher yet. How much higher? That depends. There are simply too many variables to permit a blanket statement. Is the hauling line braided or laid? Braided is better. Is it "dynamic" (stretchy) or "static" (low‑stretch)? Static is better. Is it dry or wet? Wet is better. Is the 'biner made from round rod stock or squarish bar stock? Round is better. And what is the angle of pull? The greater it is, the less the "angle of contact" and — all else being equal — the less the frictional force.
I could go on, but you can see the problem, I'm sure. To learn more about this wonderfully complicated subject, check out "The Mechanics of Friction in Rope Rescue." (Warning! This is a 464 KB PDF document.) And be sure to read the relevant sections of Charlie Walbridge's Whitewater Rescue Manual, too. But for what it's worth, here's my solution: If I'm paddling a steep, fast‑moving river, I'll bring a full complement of rescue and salvage gear: a long static hauling line, an assortment of pre‑tied slings, and "rescue quality" pulleys. But if I come to grief unexpectedly on what I thought was an easy backcountry jaunt, or if I've suffered an attack of brain‑fade and left my salvage gear at home, I'll do the best I can with whatever I happen to have on hand, even if it's nothing more than my tracking line and a couple of 'biners.
This pragmatic approach probably stems from my early introduction to rope work, back in the days when I was more interested in climbing up mountains than I was in paddling down rivers. Those were…
Indeed. And many of the skills I learned while scaling cliff faces and clawing my way up frozen waterfalls are equally useful on the water. Come to think of it, though, there've been a few times when my paddling trips have involved more than a little climbing, not to mention hauling boats and gear up sheer canyon walls. And the Z‑drag has a role to play here, as well. As Pat Roy's letter reminded me:
I was involved in a Search and Rescue organization here in Maine. A Z‑pulley system was one of our tools in raising and lowering in the vertical environment. Of course it is just as handy in the horizontal. We used pulleys if we had them handy to reduce the friction on the lines, and I recommend locking carabiners. It is amazing what induced vibrations will do to the gate of a carabiner. The humble prusik was another of our tools as rescuers and in sport climbing.
Read and heed, folks. Pat makes a very good point here. If you have locking 'biners, use them when you set up any drag system. And if you don't — and you don't plan to buy any — at least double up your regular 'biners, opposing the gates. It's surprisingly easy for a hauling line to work its way through the closed gate of a single 'biner when under tension, and while the resulting failure probably won't be as catastrophic as it would be on a mountainside, it won't exactly be good news, either.
If it's starting to seem like setting up a Z‑drag is a fussy business, that's because it is. All aspects of salvage and rescue require exhaustive (and sometimes exhausting) attention to detail. Which raises another question:
No, I'm not suggesting that you abandon your pinned boat to the mercy of the river, let alone leave an unfortunate companion to sink or swim as fate decrees. But some readers may well be wondering why they should bother with a Z‑drag at all. Brad Everson of Aurora, Colorado, put the matter succinctly:
What's the disadvantage of hooking the second carabiner [directly] to…the bow or stern of the kayak instead of using the prusik hitch?
Good question. Why bother with the prusik and sling of the Z‑drag if you can just clip a 'biner or pulley to the bow (or stern) of the stranded boat and rig a conventional 3:1 hauling tackle? Well, why indeed — if you have enough line and if you can easily get back out to your boat to reeve that line. The problem arises — and the Z‑drag comes into its own — when one or the other of these conditions doesn't apply. Assuming that a salvage line is already attached to the stranded boat, a Z‑drag can often be rigged without so much as getting your feet wet. And it conserves line: the haul rope doesn't have to be run all the way back out to the boat to yield the sought‑after 3:1 mechanical advantage.
So… Is the Z‑drag always needed? No. But there are many times when it offers real advantages. It's not a one‑size‑fits‑all solution. Salvage and rescue operations invariably require some degree of on‑site improvisation, and the Z‑drag is just one tool in the boater's toolbox. Which is why hands‑on practice under the watchful eye of an experienced instructor is so important. It's also important — critically important — not to get lost in the details. They're vital, to be sure, but in planning a salvage operation, you also have to keep the big picture in mind. After all, no chain can be stronger than its…
And I have Tony Kuhlman of Grand Ledge, Michigan, to thank for pointing this out:
I really liked your article on the Z‑drag technique to get a kayak or canoe out of a jam. It's simple, ingenious, and so obvious. But one thought that came to me is that the weakest link in the whole setup might be where the line attaches to the boat. On my cheap little plastic kayak, the bow and stern carry‑handles are attached by a fairly thin synthetic cord. If the boat is pinned in tightly, I can imagine that the Z‑drag technique could create enough force to break that line, or even tear it out of the hole where it attaches to the boat. Anyone who uses this should give a bit of thought to how they attach it to the boat, or they may just retrieve a scrap of rope and plastic, and 99.9 percent of the boat will still be out there in the river.
How true. In fact, Farwell once ripped the pop‑riveted deck right off a Tripper in an ill‑thought‑out salvage attempt. It's not a mistake he's keen to repeat. And that's not the only one. After being caught short once too often, he never wets a paddle without making sure he's got a long line in his boat. But exactly…
How Long Is Long Enough?
Reader Arnold Larsen wanted to know, too. Rather than my putting words in his mouth, however, let him speak for himself:
Fascinating article. … Your advice about not trying this system without proper instruction and experience is right on. I do have a few questions or observations, though.
Depending on how far the pinned boat is from shore and a proper anchor, it seems to me that a very long rope would be needed. Have you got a recommendation as to how long a rope one boat should carry? I suppose that ropes could be joined and run through the carabiners. [And] what is the best distance from the boat connection to the prusik hitch? Might it make sense (or not) to use a third carabiner to attach the rope to the boat, possibly making it quicker and easier in turbulent water to hook the rig to the boat?
OK. Arnold's letter raises three questions, and I'll take them one at a time, beginning with "How long is long enough?" There's an old adage among climbers and sailors that all ropes are too short, and I won't argue with that. For want of anything better, though, paddlers often use the rescue lines from their throw‑bags to winch their boats off rocks, and the de facto standard for throw‑bag lines is now around 70 feet. That's probably close to the maximum useful length for a throwing line, but I'd call it a bare minimum for salvage operations. A line that's twice as long wouldn't be too long. In fact, a 150‑ or 165‑foot rope can come in mighty handy, particularly on multi‑day expeditions or big rivers — always provided that it's a low‑stretch line of adequate strength, of course. In any event, don't count on joining up several short lines to make a long one. Knots won't run through carabiners or pulleys, and each knot is also a potential failure point. As we've already seen, the Z‑drag conserves line. That's one of its signal advantages. But you still need a long enough line to begin with.
Now let's move on to Arnold's second question: Where should you place the prusik in setting up a Z‑drag? Ideally, the "working parts" of the 'drag are assembled on shore. (I'm assuming the haul line is already attached to the pinned boat.) It's no fun trying to loop a prusik over a taut line while you're standing hip‑deep in a fast current, struggling to stay on your feet. This dictates a close‑in placement, however, and it requires frequent repositioning of the hitch as the line is taken up. A second, braking prusik (NOT shown in the schematic drawing reproduced at the start of this column) must then be employed, making it possible to reset the hauling prusik as often as necessary. It's a tedious business, to be sure. Progress is slow and gains are often measured in inches rather than feet. But it's still progress. And a few inches of movement are often enough to break a pinned boat free.
Lastly, can you use a 'biner as a bow shackle? Sure — though for maximum safety it should be a locking carabiner. That said, and bearing Tony's earlier note in mind, it's best not to depend on bow or stern grab loops as hauling points unless you're confident they're bombproof. Consult the Whitewater Rescue Manual for alternatives. Better yet, study the whole of Charlie's book as if your life depended on it. Because someday it just might. And be sure that you also get hands‑on, in‑the‑water practice with a boater who has several seasons of experience in rescue and salvage techniques. Some things simply can't be learned from books or videos alone.
There is, of course, much more to freeing a pinned boat than deploying an improvised tackle, however ingenious it might be. The river is always stronger than you are, and all successful salvage operations involve…
A Little Hydraulic Judo…
In which you use the river's power against itself. This was brought home to me by reader Norm Yarger, who's a mechanical engineer as well as a paddler, and who wrote to say:
I did find another way to free a pinned canoe. I was on a local trip with a youth group, and two boys got a little ahead of us. When we rounded a bend, we found they had caught a snag in the middle of the river and tipped the boat the "wrong" way. Water was pouring in. This was just a simple, vertical snag, and although the river had enough force to hold the boat, it was not strong enough to take it down. And definitely not a strainer, thank goodness.
The river was not very deep here and was generally docile, so we waded out to the boat, but there were no trees for a Z‑drag, and I don't think we had any rope even if there were. … After looking the situation over, I had the boys push down on one end of the boat, submerging it further while others of us lifted up on the other end. This put more river force on one end and less on the other, and the river pivoted the boat around the snag and back in line with the current. The lesson? Don't fight the river, it will usually win. Rather, use the force of the river to your advantage.
Simple and good, right? The same approach can also be used in runoff‑swollen spring torrents that no sane paddler would think of wading. Here, though, it's an adjunct to winching operations rather than an alternative. The key lies in positioning your haul line so as to make the most use of any current differential. It also helps to wrap the line right around the stranded boat, in order to (1) distribute the load and (2) spill water once the Z‑drag begins to take up the strain. Charlie Walbridge calls this "Wrapping for Revolution." I call it the "Rope Trick." Whichever name you favor, it's a clever dodge, and Charlie's invaluable Manual will tell you how it's done. He also describes another "Rope Trick" — the "Steve Thomas Rope Trick" — for getting a line around the swamped boat in the first place. And that's a very neat trick indeed. So read the book! You won't regret it.
Extracting a broached boat from the embrace of a midstream rock is always going to be a drag, but the right tools can make the job both easier and safer. When, a couple of months back, I mentioned the Z‑drag in passing in an article about the prusik hitch, I didn't think much more about it. But readers did, and that led to a second article. And that article… Well, here we are. A hearty thanks to everyone who wrote in. Your questions and comments have taught me a lot.
And now, here's my very last word on the subject: The Z‑drag and related salvage and rescue techniques are vitally important to boaters who put themselves in harm's way. They can't be learned from a column like this one, however. By all means consult specialist publications to familiarize yourself with the necessary tools and methods, but don't stop there. Get your feet wet. Seek out hands‑on instruction from somebody who knows the ropes. Accept no substitutes. It could be a matter of life and death. 'Nuff said? I hope so.
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