In the Heavy Transport and Rigging world, all types of equipment are necessary – gantries, skid steers, transporters, cranes… the more diverse toolbox a company has, the better the chance of winning projects and successfully competing in the marketplace. The tough decision is – even if you have all this equipment, how do you choose what to use? What saves the most time, costs less, is available? How do you decide which method of completing a project is the best?
Let’s take a typical Crane & Rigging project – changing out a blown transformer in a live substation.. In this case, there are multiple equipment options that could all be equally feasible to use.
Let’s limit the discussion to two choices: A crane or a skidding system. Both are indispensable assets to any contractor, but each have their pros and cons. Cranes are versatile and powerful, and one of the most common and useful pieces of equipment on a construction site. They are also one of the most expensive systems to mobilize. They take up massive space for set-up and need overhead clearance. A crane starts sounding a little high-maintenance: “I need a skilled operator. I need nice weather. I need space and time. I need solid support.”
A skidding system (or Jack and Slide system) moves a load horizontally along a guided path and over a controlled friction surface. They can slide extremely heavy objects without external forces such as hold-backs, complicated set-up or other heavy equipment to mobilize. It starts sounding pretty low maintenance… “Just let it slide. I don’t need anything holding me back. I’ve got it all under control”
The biggest contrast between cranes and skid systems is of course the word “horizontal”. A skid system cannot place an item at the top of a skyscraper or move omni-directionally like a crane.
But back to our example. Let’s consider the mobilization costs, space restrictions, schedule constraints and required crew expertise.
Mobilizing a crane is always expensive. And that’s if there is one readily available. When a transformer quits every lost production minute counts and the Utilitity loses thousands of dollars. They want a fast change-out.
In a live substation, a contractor deals with overhead wires, walls, pits and countless other obstructions. This can make maneuvering a crane extremely dangerous. A crane needs a qualified Operator and crew. Again there are issues of availability and cost.
A skid system works with a very low-profile – between 2” and 8” depending on the design and are ideal for tight or confined space with no overhead clearance. Mobilization is very fast and requires little heavy equipment to set up properly. Some designs can even span large gaps or pits. A skid system requires only a minimum of a 3-person rigging crew – an operator, a signalperson and a spotter. No special training is required to use these systems.
In an application such as this, bringing in a crane just isn’t economically feasible or the fastest solution. It also isn’t the safest solution. This could have just as easily been written on some other equipment options, such as rollers or gantries, but we’ll have to save that for another day.