Equipped with platforms extending more than 180 ft up and rugged running gear that is fully drivable at that height, the Genie machine, introduced at the Bauma exhibition last year, and the JLG unit, which debuted at Conexpo this year, have rapidly advanced the capabilities of telescopic boom lifts. Three decades ago, most machines could reach only 80 ft, but electronic controls, high-strength steel and other hardware have pushed the limit to extremes.
Terex unit Genie and Oshkosh unit JLG set a high bar. "When we got to 120 feet, people thought technology couldn't support it to go any higher than that, and, here today, we are at 180 feet," says Guy Ramsey, publisher of trade magazine Lift and Access. Ramsey organized the event late last month and invited ENR to help run tests, such as verifying specifications and timing cycles—with the full cooperation of the manufacturers.
The testing took about a day to complete. I was one of several judges, including safety and fleet experts from Sunbelt Rentals, Hertz Equipment Rental, civil contractor Traylor Bros. and forensic engineering consultant Wiss, Janney, Elstner Associates. I did not take the controls of the machines, although, at one point, I did drive a scissor lift to gain access and measure the pivot heights of the giant booms. Otherwise, I rode with the manufacturers' qualified operators. Ramsey had appointed me the group's official scribe, so I concentrated on accurately recording the results of our tests and taking note of judges' impressions.
The test methodology was simple, and most trials required common hand tools, such as laser range finders, tape measures and smartphone stopwatches. We ran each machine through paces intended to verify its published specifications, such as platform height, and generated useful, not publicly available data, such as lifting speed, so that we could help real-world users become better informed. If requested, we allowed the manufacturers to retake a test, and if any data were called into question, the judges averaged results.
The first test measured the maximum travel speed of each machine. Typically, to avoid catapulting the driver, boom lifts automatically cut ground speed as operators raise the platforms, so we timed the machines on a paved, level surface with the booms retracted but high enough for visibility while driving. Each machine traveled a straight distance of 50 ft several times. We averaged the results and calculated them in miles per hour.
Both machines performed slightly slower than their published specs (see chart). In one instance, the JLG unit automatically cut its drive power to a creep before taking another run because the operator had swung the boom around 180°. This electronic safety check hinted at the level of sensor intelligence that we would later observe from the 1850SJ.
Like Swiss army knives, boom lifts are called upon to provide versatility, a charge that includes ease of transportation on and off the jobsite. Many boom lifts, which are often rental items, include axles that tuck in for speedy and cost-effective redeployment to the next job. Yet, until now, engineers have struggled to design lifts taller than 150 ft because the large chassis required to keep the machine stable on the ground could not compress easily to fit on a standard tractor-trailer.
The super-booms dazzled us in this regard. Both Genie and JLG employed an innovative X-shaped chassis, which pivoted the four axles to provide a machine transport width of roughly 8 ft and a working width of about 16 ft. Operators achieved this geometry by driving the machines back and forth several times until the base units' hydraulic rams had sufficiently pushed or pulled on the axles. Genie employs one ram per side; JLG has two.