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As ships get bigger, tugs and towing gear must also increase in size

TUGS are rapidly evolving and gear is getting proportionally larger to serve the new generation of containerships, reports Workboat magazine of Portland. Maine.

Today, tugs are typically being designed with twice as much power as 20 years ago with bollard pulls escalating, said designer Robert Allan.

The need to handle 18,000-TEU ships is the big driver, he said.

Washburn & Doughty Associates Inc, East Boothbay, Maine, builds 93-foot long by 38-foot wide Z-drive tugs for Moran Towing and other customers.

The shipyard's executive vice president Bruce Washburn said the 6,500-hp threshold poses a challenge, requiring much bigger Z-drives 50 tons versus around 30 tons for less powerful tugs.

Seattle-based Jensen Maritime has been designing new escort tugs like the 100-foot long 40-foot wide Brian A McAllister and Rosemary McAllister, being built for McAllister Towing by Horizon Shipbuilding, Bayou La Batre, Ala.

The twin Z-drive, 6,770-hp tugs with 90 short tons bollard pull will be delivered in 2017 for offshore service, ship assist, escort, maneuvering and docking work.

Ridderinkof Winches, Hasselt, Netherlands, has designed a dynamic braking system to help these tugs handle the immense loads of postpanamax ship escort work.

"On an 18,000-TEU ship, that's a huge amount of windage," said company director Paul Schut. For an escort tug near the stern of such a large vessel, pulling a line at a 30-foot angle, losing control can lead to disaster. "Tne error and you can pull it [the tug] right over," he said.

Classification societies are looking for more powerful braking systems. "We decided it's not there, so letˇs start designing it," Schut said. They came up with a 700-mm solid steel-braking disc that can bring two to three times the braking power of similar-sized winches.

"We're saying you can do 250 tons (pull) all day," Schut said. At an estimated cost up to 40,000 euros ($45,000), "that makes it a very cheap escort winch."