Converging Cranes

When it comes to construction machinery, there often can be several tools that meet the needs of the job. But deciding which machine to use boils down to finding the best solution for the application at hand. Some job requirements are such that they fall in between two product sizes—and sometimes even two crane types altogether. As self-erecting cranes creep up in size and capacity, the lines between city tower cranes and the larger self erector categories start to blur. So when is a self erector the best solution? When is a city crane needed for the job? Here, the experts take on the issue of self erectors versus city tower cranes.

What’s the difference?

To start, both self-erecting and city cranes have a vertical mast with a horizontal jib, says Jen Smitka, Manitowoc product specialist for Potain tower cranes. A self-erecting crane is a bottom-slewing crane that’s able to erect its mast and jib without the aid of support equipment. Its reach, capacity, and ability to fit in small spaces make it suitable for a number of applications. A city tower crane is a modular top-slewing crane, ideal for jobsites with limited ground space.

The No. 1 difference between the two cranes is that the self erector literally erects by itself, says Gerry Wiebe, vice president of sales and business development for Abbotsford, British Columbia-based Eagle West Equipment, which supplies self erectors and city cranes. “It comes as a self-contained unit,” Wiebe says. “You set out the outriggers, you push a button, and the crane starts to erect itself. At a certain point you stop, you put on the ballast, you continue the rest of the erection process, and you have a ready-to-go tower crane.”

Many end users and owners recognize the cost benefits of self-erecting cranes. “The pros of the self erector [are] it’s a cheaper move-in and move-out because it’s more of a self-contained unit,” says Wayne Bylsma, president of Hampton, Ga.-based Cherokee Erecting, which rents both tower cranes and self erectors. “And it also is cheaper because it doesn’t take an assist crane to erect it, so that brings down costs for erecting and dismantlement of the machine.” Additionally, if the self erector needs to be moved on the site, he says it’s easier to relocate and far less expensive.

The ease of erection with a self erector lends the crane to high productivity. Manitowoc, Wis.-based Manitowoc Co.’s Potain mobile self-erecting units travel and set up quickly and are capable of doing multiple jobs in a single day, according to Clay Thoreson, vice president tower crane sales and marketing for North America. Self-erecting cranes also can be erected to suit the jobsite requirements. Some models offer multiple jib lengths with obstacle avoidance and raised jib positions, small footprints, and impressive reach capacities that make self-erecting cranes ideal for many situations, he says.

But while being convenient to set up and easy to move on jobsites, self erectors have an upper limit as to how much they can do. The one con Bylsma hears is that the self erectors aren’t big enough and don’t have enough capacity—so again, it’s a matter of finding the right crane for the job. “Once we get the parameters of the project, then we can distinguish which one is more applicable,” he says, noting the company asks its clients the maximum height of the project, the required horizontal reach, and maximum capacity at that length. “Once they give us those three elements we can pretty much distinguish if a self erector’s going to be more beneficial or if they’re going to have to go with a city crane.”

It comes down to three questions that define which crane will fit the project better: What’s the maximum height of the project, how much horizontal reach do they need, and what’s the capacity at that maximum reach? “If they say we need 5,000 pounds at 150 feet, we know right away that a self erector’s never going to do that because the max horizontal jib is 147 feet, so that automatically takes the self erector out of the equation,” Bylsma says.

City cranes have the larger capacities, more height, and farther reach that some larger projects need. City cranes are also typically modular, so they can be erected to meet a specific jobsite’s requirements, as is the case of Potain’s city cranes, according to Thoreson. “Multiple mast configurations and jib lengths allow customers to choose the best configuration for their requirements,” he says. “City cranes are able to be erected on multiple bases: anchors, chassis or cross, and can even be erected with traveling equipment.”

Bylsma says the greater capacity of the city cranes is a definite advantage. City cranes can have a jib length of up to 180 feet, whereas the maximum jib length on self erectors is 147 feet, according to Bylsma. The longer jib length gives the city crane a greater turning radius for the project.

The self-erecting crane’s pick-up limit is 14,000 pounds and about 3,750 pounds at the tip, Wiebe says, while a tower crane can hoist in excess of 88,000 pounds on the inset and 15,000 pounds at the tip. “There’s simply much heavier engineering available in the city crane and tower crane machines than there would be in a self erector,” he says. “Self erectors are, at this time, only going to go so high, they’re only going to go so far of reach, and they’re only going to have so many pounds, so if your project works inside the machine’s abilities, it’s an extremely cost-effective solution. If you need more height or more reach or more picking power than what a self erector can offer, then you’re definitely back into either a city crane or a tower crane, and a higher cost structure would be related with the bigger equipment.”

In addition to the height and capacity strengths of the city crane, it also scores high marks in longevity, according to Eddie Sidenstricker, sales manager, Linden Comansa America, Pineville, N.C., which manufactures city cranes. “The self erector has a lot of moving parts and pieces whereas a tower crane, you have your tower, you have your jib, your counter jib, and there’s only one moving part and that’s the slewing table,” he says. “We’ve found our cranes can last 20-30 years [when] maintained correctly.”

Of course, with the increased size and capacity of the city crane comes an added expense. It’s not only more expensive to rig, set up and tear down, with the need for an assist crane, but it’s also more expensive to ship as well.

Check out the June digital issue, page 24, for more on applications and trends in these two product categories.