Moving a 700-ton submarine on land can be a daunting task--especially when it's on land.
When the directors of the Museum of Science and Industry in Chicago needed to move one of its major attractions--a German sub captured in 1944--to a new exhibit space, they called on the services of Norsar, a heavy lift company. Norsar engineers needed a solid surface to maneuver over once the sub had been hydraulically lifted onto a dolly system. They decided to use Dura-Base mats, finding them to be the most efficient and economic way to protect the museum's grounds and to provide a secure base along the 1/3 mile haul route.
Dura-Base, a product of a Lafayette, La.-based industrial service firm named Soloco, is a system of 8' x 14' mats that overlap each other and can be pinned together to create a uniform temporary road over soft ground or difficult terrain. Versatile and reusable, the high-density polyethylene mats have been employed to allow efficient passage of heavy vehicles in all sorts of climates--from deserts in the Middle East to Amazon jungles to the arctic tundra--to facilitate foot traffic at public events, and in April 2004 to literally bear the weight of history.
The U-505 submarine had been on display outside the museum since 1954, and Chicago's brutal winters and humid summers were taking their toll on the vessel, which when constructed by the Germans, had been expected to last only five years. The institution's directors conceived of a new home for the sub by the museum's northeast corner four levels underground. Now that move is complete, their plan is to recover the lawn over the newly-dug cavity and then build a new exhibit with the U-505 as a centerpiece. Opening in 2005, the exhibit will allow visitors to drive a submarine simulator, decipher secret messages, and learn about the sub on a more interactive level.
Norsar, in hauling the sub to the rigging that would lower it into the earth, found Dura-Base mats to be ideal over asphalt and soft ground along the route. "They were exactly what I needed to protect the ground over a large area," said Ralph DiCaprio, Norsar's project manager who supervised the move. "It's not like you could throw down two mats or plates right next to each other and drive down the road, because some turns required wide areas in the haul route. When the submarine was swinging and each dolly had its own path over a large area, Dura-Base worked out nicely."
DiCaprio added that originally he planned on using steel road plates but found Dura-Base to be a superior option for a variety of reasons. Road plates were more expensive to rent, for one. Also, Dura-Base mats could be brought to the worksite more economically. He explained that only 10 or 11 plates can fit onto a truck as compared to 40 Dura-Base mats.
Furthermore, since the support base needed be continually repositioned throughout the move, DiCaprio found Dura-Base mats easy to handle; workers could move them into place more quickly than road plate. At 1,050 lbs. per mat, Dura-Base is about 75% lighter than steel plates of equal square footage.
Road plates' other disadvantage is that they can warp or "deflect" when burdened under a heavy load and then maintain that deflection. Considering that Norsar's dollies had the keel of the submarine only two inches off the ground, protruding edges caused by deflecting plates could have complicated the move.
Dura-Base also made preparing the route convenient for Norsar, especially in areas where the path wasn't level. DiCaprio said he often used gravel or other fill to grade off a depression and then laid the mats right on top. In some places, workers even stacked Dura-Base two or three mats thick, in lieu of fill material, to provide for level movement of the sub. The mats were also useful in ground transitions, such as from paved surface to a curb.
Other companies using Dura-Base for other projects have found the ability to stack them quite practical. "It's an alternative to cribbing up with plywood," said Jerry Venkus of Venkus & Associates, the Dura-Base manufacturer's representative that helped supply Norsar. "Some project managers use two entirely locked-together surfaces of Dura-Base if the soil is soft or there's a lot of water. They don't have to drag in fill."
According to DiCaprio, hauling the U-505 wasn't all that different from other heavy lift jobs Norsar has done. What was unique was the constant media attention and the audience who turned up to watch the three-day haul. In the future, for jobs both in and out of the public eye, Norsar plans to call on Dura-Base again.
"The mats are real convenient to use," commented DiCaprio. "They're something for me to keep in mind whenever we need to do load spreading and covering the surface for driving the loads over."
