“Rope Is Just Rope, Isn’t It?” (Fatzer’s Surprisingly Different Stabilo® Rope)

Stabilo rope's reliability and load capacity make it ideal for gondola, 2S and 3S cableways.

Stabilo rope’s reliability and load capacity make it ideal for MDG, BDG and 3S cableways.

Wondering whether choice of rope really matters? Look at it this way: If you were responsible for building a tram in your city, wouldn’t you want to know all you could about the track?

Awhile back, the Gondola Project posted an article about the often-overlooked issue of the weight-bearing cable or “rope” is it’s known in this, the “ropeway” industry. The gist of the story was that choosing the wrong rope, or leaving it to the last minute, can be inconvenient at best and extremely expensive or even unsafe at worst.

Today, we begin to examine Fatzer’s individual rope products, used for ropeways worldwide — this first one is Stabilo®. Fatzer ensures us that the differences between the products are subtle but important. Having produced literally thousands of miles of rope for transporting people in cable cars and chairlifts, they know what they’re talking about.

Most rope changes significantly with use, but not Stabilo. It remains, well, stable.

All ropes are made up of many wound strands of wire. Often, those strands are wound round a core of different materials. After the rope is put into use, the rope continually bends at the ropeway’s wheels. Friction from contact with the between strands of wire creates minute notches on them. The notches begin rubbing against each other, eventually breaking the wire.

Polyethylene core stabilizes movement and reduces elongation. (Photo from

Polyethylene core stabilizes movement and reduces elongation. (Photo from

Furthermore, with repeated cycles the strands quickly begin settling. Eventually they work their way into the core, changing it, narrowing its diameter and elongating the rope. The entire set of issues lessens the life expectancy of the rope.

Fatzer’s solution? Stabilize the core and prevent contact between the wire strands.

A Stabilo rope’s interior is filled with a polyethylene core rod, which is heated during the formation process. What results are compressed and minuscule layers of plastic between the strands, which are now kept separate at a uniform distance. So there’s a stable diameter at the core of the rope, for a weight-bearing cable that is less prone to stretching and, therefor, longer lasting.

The ideal applications for Stabilo ropes are continuously circling cableways, which demand longer and uninterrupted performance. All ropes stretch, though. Eventually even Stabilo requires maintenance for shortening (and ultimately replacement). Stabilo is the right choice for a ropeway that can only be halted at specified, predictable periods. Learn more here.

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Aerial Technologies, Lesson 3: BDG

The Ngong Ping 360 is a high profile example of bicable technology.

Note: This post was updated on May 30, 2011. These revisions reflect the most current and available knowledge we have but do not guarantee the validity of the claims made. As always, it’s best to use the information contained herein as a guide.

Bicable Detachable Gondolas (BDG) are a less common form of gondola than Monocables (MDG). Originally, BDGs were a superior technology to the MDG, but advancements in MDG technology have rendered the BDG obsolete in all but the most specific of situations.

The difference between MDG and BDG is straightforward. Whereas Monocable systems are both propelled and suspended by the same cable, Bicable systems provide those two separate functions with two separate cables.

One cable is stationary and doesn’t move. It’s this cable that gives the gondola support. This cable acts much like a rail would for a traditional transit vehicle. A wheeled bogey attached to the gripping mechanism of the gondola runs along this cable much as train’s wheels would run along rails.

The second cable is not stationary. It runs in a loop and is powered by bullwheels at the terminals. The gondola grips attach and detach from this moving cable, thereby providing propulsion.

BDG Stats:

  • Maximum Speed: 27 km/hr (revised upwards from 24 km/hr).
  • Maximum Capacity: ~4,000 pphpd (revised downwards from 6,000 pphpd).
  • Vehicle Capacity: Up to 17.
  • Wind Stability: Operational in winds up to 70 km/hr.
  • Maximum Span Between Towers: Up to 1,000 meters (conditional on capacity).
  • Cost: $15 – 25 million (US) / kilometre. (estimate).

While Bicable systems are more expensive than Monocable systems, this added cost is not really justified. The only two real advantages of a Bicable as compared to an MDG are as follows:

  • Bicables can travel at greater maximum speeds than the MDG. This speed premium, however, amounts to only 5.4 km/hr.
  • Longer spans without need of intermediary stations. Like above, this premium is modest. Whereas an MDG can span 700 meters without need of an intermediary tower, the BDG can span 1,000 meters.

These modest advantages are offset by the following:

  • Higher capital cost
  • Larger station size
  • Larger tower profile.

Because of their higher capital costs as compared to an MDG, with little real advantage, Bicables are increasingly becoming an abandoned technology in the cable transit world.

The Teleferico Madrid is an old but strong example of bicable technology.

Proceed to Aerial Technologies, Lesson 4: Funitels

Return to Aerial Technologies, Lesson 2: MDG

Creative Commons images by jaaron and Shadowgate.

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Aerial Technologies, Lesson 2: MDG

Teleférico do Alemão in Rio de Janeiro, Brazil (2011). At 3.5km, with 6 stations, it is one of the world's largest CPT systems. Image by Flickr User minplanpac.

Monocable Detachable Gondolas (MDG) are likely the most common CPT system you’ll encounter as their low cost has made them an attractive addition to public transit systems in the developing world. Systems like the Medellin MetroCable, Telecabine de Constantine and Caracas Metrocable all use MDG technology.

Characterized by a detachable grip which allows for intermediary stations and corner turning, MDG’s utilize a single cable (hence, monocable) for both propulsion and support. This means that the cable that pulls the vehicles is also the cable that supports the vehicle.

MDG Stats:

  • Maximum Speed: 22 km/hr.
  • Maximum Capacity: 3,000 persons per hour per direction.
  • Vehicle Capacity: 4 – 15 persons.
  • Cost: $5 – 20 million (US) / kilometre.

MDG’s suffer from a relatively low capacity (though still comparable to many urban tram routes) and given their single cable are prone to stoppages due to winds in excess of 50 km/hr. MDGs are therefore most useful in calm wind environments with low capacity needs.

As the investment is quite low compared to other technologies, MDGs are excellent “starter” systems for cities intrigued by the technology but question its effectiveness. A short, low-capacity feeder line, for example, would be a fine place for cities to experiment with MDG technology.

The Medellin MetroCable is one of the world's most successful Cable Propelled Transit systems. It utilizes MDG technology.

Proceed to Technologies Module, 3: BDG.

Return to Technologies Module, 1: Introduction

Creative Commons images by Big C Harvey and Felimartinez.

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Cable Shut-down

Yesterday, in Lenggries Germany, a gondola system malfunctioned stranding dozens of riders in mid-air. Helicopters were were used in the rescue. There were no injuries. The system was built by a subsidiary of Thyssenkrupp, a manufacturer with little experience in cable transit.

Detractors of cable technology – I’m certain – will use this as evidence that cable technology is not reliable or safe, but the facts suggest otherwise. Problem is, those facts are too often silent.

In his book, The Black Swan, the philosopher, empirical skeptic and financial guru, Nassim Nicholas Taleb describes a phenomenon called Silent Evidence. Silent Evidence is a body of evidence on any given topic that fails to present itself because no one ever talks about it. For example, in the realm of entrepreneurship (he states), we believe risk-taking to be an inherent quality of a successful entrepreneur. Problem is, it’s a dubious claim because there have been literally millions of risk-taking failures but because we never discuss those failures, the evidence they offer becomes “silent” and doesn’t count.

Same deal for cable.

There are tens of thousands of cable systems around the world, the vast majority of which never receive an iota of attention because nothing remarkable ever happens to them. But the moment a problem does occur – as did yesterday – the media pounces.

But does the media respond over a jumper on a subway platform? How about a mid-intersection fatality caused by a light rail vehicle? How about a car crash? How about an hours-long service disruption? How about a Windows computer virus?Of course not. Why? Because those incidents are common; they happen everyday.

There’s a simple rule that can tell you all you need to know about the safety and reliability of any given technology: The degree of media coverage a given technology’s failure causes is inversely related to the chance of that failure’s occurrence.

That’s why we read about airplane crashes; they’re exceptional. If they happened every day, we wouldn’t be interested.

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