By Alice O’Riordan, B.E.
There is much more to outriggers these days than simply extending them as part of the step by step set up of the mobile crane. The outriggers had a very black and white existence for many years; they were either half extended or fully extended. Fully extended was the recommended position as it provided the most stability. A crane’s stability is not only effected by reaching out for the load but also by slewing and it is this that the operator is constantly monitoring while being guided by the person banking them. The outriggers provide that extra stability when the crane slewed to the side and a fully extended set of outriggers, widens the base and reduces the possibility of overturning.
However fully extended outriggers can mean you add at least an extra 4m to the width of the crane. That 4m may not be possible in a set up area.
Take a city refurbishment project or shutdowns in industrial areas where space is limited and often a crane may not have the luxury of fully extending the outriggers. Operators may have to reduce the outrigger extension on one side by say 30%, i.e. 70% outrigger extension. In previous situations, the crane operator’s handbook for operating the crane listed calculations for either half or fully extended outriggers, so the client was losing out on crane capacity as the operator would have to choose the 50% option for calculations on the retracted side when really it had a 70% capacity. That 20% extra capacity on one side was ignored and could mean having to use a bigger crane for the lift just because there were no calculations available for 70% capacity.
Liebherr took on this design challenge and revealed a ‘VarioBase®’ system at Bauma in 2010 that is now the norm - not only in Liebherr but all the latest crane models. VarioBase works by using sensors on the outriggers and the slew ring that monitors the percentage of extension of the outrigger as well as the pressure changes in the outrigger as the crane slews. This is happening in real time so unlike the older version where the set up was locked into a conservative, bottom-line load chart for the 50% extension before the lift began, now this information is fed to the operator as the lift happens and the crane can work safely within the crane capacity by monitoring pressures for the exact percentage of outrigger extended.
VarioBase is fitted as standard in cranes models now as it is felt in the industry there is no benefit to have this as an option that could be removed simply for cost saving purposes. Its advantages for both client and contractor are immediate from pricing the most accurate crane for the project to the operator being able to monitor, second by second, precisely what is happening at all corners of the crane as the lift is happening ensuring a safer lift.
Finally, because the question always comes up: there is the option of not using the outriggers at all. While manufacturers have calculations provided for this option it is for a limited crane set up; for example, the crane is locked at 0 degrees and cannot slew. In reality this is not a safe option and rarely if ever considered. It might not be supported by insurers of lifts for that matter.
There are a lot of old YouTube videos of cranes on their sides where the importance of extending outriggers was ignored – often a “quick” job that saw setting up the outriggers as taking too much time to carry out. Omitting that step or only partly extending the outrigger by guesswork has catastrophic consequences. In these videos you can see instantly the tell-tale reduced position of the outriggers if they are not buried too deep in the ground.
VarioBase might hopefully see an end to any new additions like these to YouTube.
Note: The title VarioBase® is trademarked to Liebherr