Monday, May 10, 2010


Crane mats, floats, outrigger pads – call them what you will, but if you own a boom-truck, you should have a set or two with your crane at all times. It’s almost like carrying a portable foundation.

The steel foot pads on the end of crane outriggers – from the factory - are generally small and are designed for good ground conditions. “Good ground conditions” is a loaded phrase that requires some consideration.

You can gain valuable insight into the ability of soil to support loads by referring to OSHA 1926, Subpart P, Appendix A. Find more info on the calculations here. Among the many responsibilities of the crane operators is his or her ability to be able to assess the ground area in which they will be setting up. The ground surface must have enough stability and bearing capacity to support the dead weight of the boom truck, the load, the rigging, and shock (impact) loads and any dynamic conditions such as swinging, hoisting, lowering and traveling.

It is pretty obvious that the ground pressure developed by a crane on its outriggers is huge. As the load is swung around and the crane rotates over the various corners, those pressures are not equal over the outriggers and indeed vary based on the operating conditions and quadrants, for example, there may be times when only one outrigger is taking the majority of the weight of the crane and the load.

If the ground under that outrigger is not firm, level and well compacted, that outrigger can punch through the ground and cause catastrophic crane failure.

Questionable but otherwise reasonable ground requires the use of outrigger “floats” or “crane mats” which are placed under the outrigger pad to disburse the weight of the crane and the load over more ground area than just the steel pad. Crane mats and floats should be made out of substantial materials – generally dense wood, high pressure plywood or composite materials and they must always be larger than the outrigger, factory foot pad. We have seen “home made” outrigger pads made out of pressure treated pine and we suggest that this is a very bad idea. While it may work in a muddy field with a small load, that pine is a soft wood that will compress or shatter when it comes into contact with something solid such as clay, tree roots, boulders, broken concrete or bedrock – while the weight of the outrigger is pushing from above.

Undeniably, many soils on a job site are questionable, so pro-active safety management requires the use of supplemental crane mats much of the time if not all the time. Keep in mind as well that supplemental floats and crane mats can also provide protection to asphalt and decorative stone or concrete surfaces which are easily damaged by the steel outrigger pads.

Don’t forget too, that an asphalt or paved surface like a parking lot is no guarantee that the subsurface will support the weight of the crane on the outriggers – a problem that many boom-truck owners discover as first time operators – and those hard concrete surfaces that seem indestructible may be vaulted or may be poured over a hollow drain pipe.
Many times the ground or gravel under the concrete or asphalt may be washed out in spots creating voids and potential weak spots. Your floats can spread the weight out and save you a potential insurance claim, contractor back charges, or worse.


A good operator knows that your boom truck has to be on solid level footing - always. Floats and crane mats do not change that fact and when they are in use, they must be level. Remember that if your boom truck is not set up level to within 1% (or as per manufacturer instructions) – your load chart does not apply! Be aware that in a 20 foot span, 1% is only two inches off-level! Anything past this point and your crane can lose 15 – 20% or more of the rated capacity. If your outrigger pad is set down on an unleveled float, it may slide off under load and set off a catastrophic chain of events with disastrous results.

Call our Parts Department for more information on the wooden and composite pads we have in stock as well as the special order pads or cribbing that we can order for you.

Get a set of outrigger floats for your boom truck. Operate safely, and operate smartly!

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