Outrigger
Also called Stabiliser leg, Jack leg
An extending leg or beam fitted to a mobile crane, or to other plant such as boom pumps and some MEWPs, that is lowered to the ground to widen the machine’s effective base and provide stability while working. Outriggers transmit high, concentrated point loads to the ground, which is why they are typically set up on mats or pads.
In practice
Extending the outriggers is what converts a machine that would tip into one that will not, and the price of that stability is paid at four small feet. The reaction at each foot can be several times what the same machine puts through a wheel, over a fraction of the area — which is why an outrigger set-up needs a ground check that travelling on the same site did not.
Where this comes from: Set-up practice as covered in our CPD-accredited seminar on good practice when specifying outrigger mats.
Where it matters on site
Two set-up errors recur. The first is short-rigging — extending the outriggers part-way to fit the space, which narrows the base and raises the reactions at the same time, and takes the machine off the load chart configuration it was planned against. The second is setting a foot over something invisible: a manhole, a shallow duct, a backfilled trench, a basement lid. Both are set-up decisions, made in minutes, that no mat can retrieve.