Climbing the highest mountain in Northern Europe, a few thoughts on the Theory of Constraints came to my mind. To get to Galdhøpiggen, 2469 meters above sea level, the most common route takes you over a glacier where rope teams are used for safety reasons. In his must-read book “the Goal”, Eli Goldratt (1984) uses rope teams to illustrate an efficient production system.
A rope team is a number of people who tie into a rope at equal distances to each other. If one is unfortunate and falls into a crevasse (a crack in the glacier which might be open or covered by a superficial snow bridge) the rest of the team will easily (and automatically) pull him up again. For a rope team to function at its best, everyone should move at the same speed, leaving the rope to hang relatively tight without touching ground.
Why a rope team is optimal
Some years ago, Goldratt’s book “The Goal” was among the first business books I ever read, and it left a lasting impression. The book describes how to manage manufacturing operations simply by controlling the bottleneck (the constraint) and making all other processes move clock-pulsed at the maximum pace of the bottleneck. A drum sets the pace and lets everyone know what it is. To allow for some natural variation in the processes, a small amount of inventory in-front of processes work as buffers. Finally all processes are linked together as in a rope team. Together it makes up the drum-buffer-rope concept—the manufacturing application of the Theory of Constraints.
Our glacier guide on the way to Galdhøpiggen told us that “the fastest way to move in the mountain is to move slow and even”. That is not a bad advice. It was based on his many years of experience in getting diverse groups of people up steep mountains in all kinds of weather. Manufacturing operations are similar. Goldratt’s story is about the chubby and slow kid Herbie, who is trekking with a team of stronger boys on a boy scouts excursion. This passage puts it very well (c.f. The Goal, Chapter 13-15):
The plan, I learn, is for the troop to hike through the forest following a blazed trail to someplace called “Devil’s Gulch” (…) After a few minutes, I turn and look back. The column of scouts has spread out to some degree from the close spacing we started with. Instead of a yard or so between boys, there are now larger gaps, some a little larger than others. I keep walking. But I look back again after a few hundred yards, and the column is stretched out much farther (…) I look up and notice that the boy in front of me is going a little faster than I have been. He’s a few feet farther ahead of me than he was a minute ago. So I take some bigger steps to catch up. Then, for a second, I’m too close to him, so I slow down. There: if I’d been measuring my stride, I would have recorded statistical fluctuations. But, again, what’s the big deal? (…)
Herbie falls over beside the trail, his tongue hanging out (…) Dammit, we’re going to be running and stopping all day long if this keeps up (…) Why can’t we all just walk at the same pace as Ron [in the front] and stay together? (…) That’s when I begin to understand what’s happening. (…) Our hike is a set of dependent events… in combination with statistical fluctuations (…) What if I were to say that this troop of boys is analogous to a manufacturing system; sort of a model. In fact, the troop does produce a product; we produce “walk trail”. (…) The idea of this hike is not to see who can get there the fastest. The idea is to get there together. We’re not a bunch of individuals out here. We’re a team.
“Now listen up!” I say. “This is the order you’re going to stay in until we reach where we’re going. Understood? Nobody passes anybody. Everybody just tries to keep up with the person in front of him. Herbie will lead!” Everyone else looks aghast. “You want him to lead?” asks Andy. “But he’s the slowest one!” says another kid. (…)
We’re flying now, doing twice the speed as a troop that we did before. And we still stay together. Inventory is down. Throughput is up. Devil’s Gulch is lovely in the late afternoon sun.”
A rope team helps set a controllable pace in the troop of scouts and in a manufacturing plant. To achieve a “swift even flow” is a core idea in the Theory of Constraints, as it also is in mass production, just-in-time manufacturing, lean production, six sigma, and mass customization. It is a generally accepted theory in operations management. If you want to be efficient, go for the idea of a rope team!
Why a rope team is no Nirvana
On the way down from Galdhøpiggen I took the opportunity to do a little research. Using my trekking company as a focus group, I asked a simple question: “So what do you think about tracking in a rope team? Was it fun?” The answers came quickly: “It’s boring”, “I’d rather walk in my own speed”, “It’s neither good nor bad” and “It’s OK at first”. I must admit I also found it boring.
The speed was slower than my usual pace, but, even worse, it was not rhythmic. Stop and go, go faster, go slower. One reason for this was that the team was diverse—young and old, strong and not so strong—which caused variance in pace. Second, I walked at the end of the 30 man rope team, suffering under all the co-variance of the team. I compensated the boring and varying pace by holding pieces of the rope in front of me in my hand (building “inventory”), and then let some rope out when the pace suddenly increased.
This, of course, is an absolute “no go”. If all do this, the takt system does not work. In fact, the bullwhip effect would make sure its no fun to walk at the end (maybe people in front of me did it as well?) The worst thing with people building “personal inventories” in rope teams is that it can have catastrophic consequences, because the rope team does not work as intended if people break through snow bridges. People should not do it, but I understand why they do so. Variances increases—so does co-variances—but it still feels more fun for the individual.
Rope teams are efficient and safe. For crossing glaciers there is no good alternative. It just so happens that it is often boring, making people forget about their tasks and start thinking on other remote things… like writing blogs….
Goldratt, E. M. & Cox, J. (1984) The goal: excellence in manufacturing, Croton-on-Hudson, N.Y., North River Press.