Ocean Towing with Z-Drives

Raina O Clark
Monday, October 03, 2011

Western Towboat leads the way with tractor tugs.

 

For a first-hand look at how tractor tugs are used for ocean towing on the West Coast, I took a ride on the first Titan class vessel built by Western Towboat out of Seattle, Wash. The 108-ft Western Titan was built in 1997 with stern Azimuth drives. She pulls a container barge the size of a football field on a tow line from Seattle to Skagway, Alaska, making several port calls along the way and traveling through both the inside passage and waters more open to the Pacific Ocean. On a contract with Alaska Marine Lines, the Western Titan supplies Southeast Alaska with industrial and consumer goods — everything from cars, construction equipment, mail, explosives and containers.

 

• First In: Experience Counts

Captain Chris Lickey runs this route regularly with the Western Titan and has been driving tugs for more than 20 years. “Western Towboat was the first to do line hauling with a tractor tug, to the best of my knowledge,” he told me on the first day of my trip. “The biggest strength of tractor tugs is the ability to back down and maintain control.”
The Titan class vessels are regularly able to flop alongside their barges and bring them into port without the assistance of a harbor tug. “It will be blowing 40 knots when we get to Ketchikan and we’ll bring the tow in ourselves,” Lickey told me as we neared the first stop on the tug’s route. “I’ve been on a tractor tug when it was 70 knots and gone unassisted. You wouldn’t dream of doing that with a conventional tug. One of the hardest things with a conventional tug is to get the tow stopped.” That, and “backing into the wind is brutal,” he said.

 

• The Right Technology: with caution

Z-Drives may be the right technology for a number of applications, but there are issues to consider. The drives are dynamic and have a significant impact on the way the tug rides. Consequently, the hulls of the Titan class vessels are built for stability and want to ride at the surface of the water instead of cutting through the waves. Capt. Lickey described the Western Titan as “rolly” and I have to agree. A small correction of the drives set the tug rocking — port, starboard, and then port once more before settling into its new course. Small swells of three or four feet, the kind we had encountered as we entered the more open waters of Queen Charlotte Sound off Canada, really got the boat swaying.

 

• Lessons Learned


After the Western Titan, Western Towboat began building its Titan class vessels with bilge keels, or rolling chocks, to counteract the “rolling” effect of their wide, rounded hull shape. Bob Shrewsbury, co-owner of Western Towboat, along with his brother Ric Shrewsbury, said other issues they have encountered include the necessity to overhaul Z-Drives sooner than conventional drives. Because of the design of the Z-Drives themselves, operators may not get as many hours out of the gears and bearings. However, he said, the secret is to buy a bigger unit than you think you need. Because ocean towing vessels operate on a continuous duty cycle, operators will want a drive with enough horsepower to keep it from always having to operate at the top end of its torque. This is the lesson learned from the Western Titan, which had its drives replaced with higher capacity units early on.
 

Still, according to Shrewsbury, maintenance and repair on Z-Drives is not much more complicated than conventional tugs. “It’s all just gears and bearings,” he said. Beyond having the right tools to work on the drives, Western Towboat’s engineering personnel have received training under the drive manufacturers and learned through experience in the shop.
 

Obviously, Western Towboat is satisfied with its decision to go with tractor tugs for ocean towing, despite the learning curve. The sixth tug in the Titan class is currently under construction and scheduled to launch in late October. It’s expected to be working by the end of the upcoming holiday season.

 

• New Applications: Western Leading the Way

Shrewsbury said although using tractor tugs for ocean towing was unusual back when his company began building them, the use of Z-Drives in towing applications has slowly begun to catch on. Lickey pointed out that Azimuth drives are finding their way into more applications and being used in DPS vessels in the Gulf of Mexico and even cruise ships, making harbor assists less necessary for simple dockings. “I think more towing companies down the road will start using these drives,” Lickey said, “but Western Towboat is definitely out in front on this.” Shrewsbury and his brother both drive tugs and before they began building the Western Titan they could see the potential the drives had for all kinds of work. Western Towboat’s first tractor tug was the 72-ft Westrac, built in 1988. “We didn’t see why we couldn’t do it in a larger vessel,” Shrewsbury said.


Another reason the company turned to tractor tugs was the potential for re-sale. “We were spending a lot of money to build the Western Titan and we thought if we had a large Z-Drive tug we could sell it anywhere else in the country or even other parts of the world.” Shrewsbury added, “There’s not a lot of people jumping up and down for used conventional tugs these days, and there’s not a huge difference in price between building a Z-Drive over a conventional tug.”

 

• Z-Drives: Proving their mettle and utility

My trip on the Western Titan stretched four and a half days, from Seattle to Juneau. At my final stop on Western Titan’s route, the captain was presented with a perfect, if unsolicited, opportunity to demonstrate the benefits of Z-Drives in potentially dangerous situations. The Titan, tied to the side of her barge, began entering the Port of Juneau when a cruise ship pulled anchor and started leaving its dock. The cruise ship then requested a port to port, but, in Captain Lickey’s judgment; there was not enough room to pass safely. Lickey bailed out, reversing the tug’s drives, stopping the massive barge it was tethered to and backed out of the port until the traffic had passed. “That would not have been possible in a conventional tug,” Lickey said.
 

If the use of Z-drive tugs in open water and/or long distance towing situations is not yet prevalent, it is not because the revolutionary tractor vessels haven’t shown their value. The leadership of Western Towing, coupled with the experience of their seasoned captains, has put to rest any doubts in that regard. As Z-drive tugs continue prove their mettle in any number of roles, what better place to demonstrate those capabilities than in the icy and sometimes bumpy waters of the inside and outside passages to Alaska?

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