Earlier this year Ness Cranes of Seattle, WA, sent its Grove GMK7450 (known as the Grove GMK7550 in the United States) all-terrain crane on board the U.S. Navy’s aircraft carrier, USS John C Stennis, to help erect a new mast.
Work took place at the Puget Sound Naval Shipyard just outside Seattle, in nearby Bremerton, and lasted just over a month. Ness’s directive for the GMK7550 was to replace the ship’s main mast, as the additional weight of new antennae exceeded the structural limit for the old mast. The heaviest load to be lifted onto the ship, however, was the GMK7550 itself. Weighing in at 550 ton (450 t), it is the largest mobile crane in the Grove line and had to be carried on board by an adjacent harbor crane.
“Lifting the crane onboard the ship was the most complicated part of the whole project, but having the GMK7550 on board the ship was crucial; we needed its excellent lifting capacity to take down the old mast and erect the new one,” said Kurt Kleppe, vice president of Ness Cranes.
“The engineers at Grove supplied us with all the technical information we needed to make the crane lift, such as the center of gravity, the precise weight of the crane and so forth. However difficult that aspect of the task proved to be, it was certainly worth it, as the GMK7550 worked for over a month with not one minute of down-time.”
The first lift on board was to remove the original mast, which weighed approximately 71,000 lbs. (32,205 kg) and measured 105 ft. (32 m) tall. With a 197 ft. (60 m) maximum boom, the GMK7550 was easily able to reach the necessary heights for dismantling the old mast. With this completed, the crane installed the new mast, which weighed approximately twice as much as the original at 125,000 lbs. (56,699 kg). Standing at a height of 116 ft. (35 m) tall, USS Stennis’ new mast is more than capable of handling the necessary antennae inputs and alterations.
Ness started business in 1950 and today employs 57 people and owns 37 cranes including 24 Manitowoc Crane Group products — 17 Grove mobile cranes and seven National boom trucks.