February 27, 2024

Skidding Systems Explained

Hydraulic skidding systems move all kinds of heavy loads - ranging from less than a ton to more than 1,000 tons - safely and simply.

When it comes to heavy loads, cranes are not always the best choice for horizontal load movement. Skidding systems- also called jack and slide systems- can be a great alternative when cranes don't fit or are too expensive, or when safety is critical.

Read on to learn more about skidding systems- how they work, how they're used, and what makes them an ideal choice for some jobs.

The Basics

Hydraulic skidding systems all share the same three essential components:

Tracks (yellow) that guide and support the skid shoes and load;
Skid shoes (blue) that sit on the track and support the load as it moves;
Hydraulic cylinders (silver) that push or pull on the skid shoes to make the whole thing work.

The principles behind hydraulic skidding systems are very simple- maybe even boring. But boring is a good thing on a job site, where excitement usually means that something has gone very wrong. If you're anything like us, you've seen a lot of videos of suspended loads falling due to high winds, failed rigging, miscalculation, etc. Every time that happens, it's a huge risk to personnel safety and to the load itself, not to mention that recovery is a lot of work.

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The Physics

When performing a jack and slide operation, a load is never freely suspended- that's a significant safety advantage. Typically, the load would be jacked up a few inches (just enough to slide the skidding system under it), and then lowered onto the skid shoes. The shoes are well-supported by the tracks, and the tracks are well-supported by the ground, a floor, or some kind of blocking.

From there, the forces acting on the system are simple: the force of gravity directed downward, the push (or pull) force of the hydraulic cylinder to move the load, and the force of friction resisting the load's movement. The forces are entirely contained within the system, so no external holdbacks are required.

One further benefit: that all of Hydra-Slide's systems are designed so that the hydraulic cylinders self-reset after each push or pull stroke. After setup, the entire skidding operation is controlled from the hydraulic pump and personnel can stay well clear of the moving load.

We're often asked if we recommend adding grease, soap, or another lubricant to the track to make things move more easily, and our answer is a resounding no- friction is a good thing!

The hydraulics are always pushing against resistance, so as soon as the hydraulic power is turned off, the load stops. If anything goes wrong with the hydraulics or the skidding system, the load stops. Put another way- as long as the system is set up and used correctly, catastrophic failure is very, very unlikely.

The coefficient of friction between skid shoe and track is relatively high- around 10-20% depending on the exact system and the conditions.

Heavy Work

Skidding systems have seen constant use on job sites since the 1980s, and the earliest systems were designed to be durable, versatile, and capable of handling oversized and superheavy loads.

One of Hydra-Slide's founders, Don Mahnke, was a pioneer in this field, and while we've made a number of improvements since the first skidding systems were built, the overall design has changed very little. As they say- if it ain't broke, don't fix it. Some of our customers have skidding systems that have seen constant use for 20-25 years that are still going strong!

(Photo) Here you can see part of a tunnel boring machine (TBM) loaded onto our HT500 Heavy Track system. The skidding system was used in conjunction with a crawler crane, a hydraulic gantry, and other equipment to bring the TBM to site in pieces, lower down a shaft, and assemble and skid the full 670-ton machine into position underground.

The normal capacity of the HT500 system is 500 tons, however here, the system is used in combination with our JLS250 Jacking Load Shoes to both increase the total load capacity and provide more precise control of the load.

Tight Spaces

Skidding systems aren't just for super heavy work, though. To meet the needs of our customers, we also have a line of hand-portable Low-Profile Skidding Systems for smaller loads, constrained or sensitive work sites, and any situation where portability is crucial.

In the field, smaller loads are often moved using dollies, rollers, air skates, or improvised methods. These approaches can be effective, however they all tend to work by reducing friction and making the load easier to move. This means they all have the same potential drawback in terms of safety: a load that moves easily, can easily run away or move in unwanted directions. In contrast, a skidding system's high-friction design ensures that the load movement is slow, controlled, and only in the intended direction.

Of course, loads that specialized riggers would consider small can still be pretty big to most folks. While Hydra-Slide offers a specific solution for loads 30 tons and under, we also have low-profile, hand-portable systems with load capacity up to 350 tons.

(Photo) A Hydra-Slide XLP150 Extreme Low-Profile system doing a fantastic job of sliding a small power transformer down a hospital hallway. For a job site like this, equipment options are limited- the fact that the skidding system could be carried in and set up entirely by hand was a major advantage.

At Hydra-Slide, designing and building skidding systems is all we do, and we're passionate about our business.

If you want to know more, we'd love to hear from you.