Z-drive barge extends life of single-screw tug

Marcon International recorded 441 tugs for sale worldwide in its July 2004 market report. Of these, 162 were still single-screw boats. A number of innovative companies have found ways to upgrade and use these vessels in contemporary situations.

The barge can carry up to 54 trailers.
   Image Credit: Alan Haig-Brown

In some cases, where the hull has enough beam, tug owners have repowered their single-screw boats with two engines and props. In British Columbia, Seaspan International, a Washington Marine Group company, has found a unique and dedicated use for its 34-year-old 2,500-hp single-screw tug Seaspan Challenger.

Vancouver Island, just off the coast of southern British Columbia, has a population of more than 750,000. Because very little of the island’s 12,407 square miles is farmland, the island requires dozens of truckloads per day for groceries alone. Consumer goods and construction materials add up to dozens more trailers every day.

While the government-owned British Columbia ferry system provides space for some trucks amongst the cars, the private sector has found increasing opportunities in the transport of trucks and trailers between the mainland and the island. The island is also a major source of fisheries and forest products that are trucked back to the mainland.

Seaspan Coastal Intermodal operates six vessels from a site near the mouth of the Fraser River, delivering trucks and trailers across the Gulf of Georgia to southern Vancouver Island ports. Four of these vessels are self-propelled ships between 325 and 386 feet long. One is a towed deck barge and one is an articulated tug-barge unit. The ATB has the largest capacity of all six vessels. The 456-by-82-foot barge Coastal Spirit will take up to 54 45-foot trailers. When the barge is mated to the 131-by-32-foot Seaspan Challenger, the two vessels have a combined length of 530 feet. Although the relatively shallow barge has a waterline beam of only 61 feet, this would still be way too much barge for a single-screw tug to handle in the river current and docking slips.

The solution is elegant. A Rolls-Royce z-drive is built into the bow of the barge. Powered by an 1,800-hp Cummins KTA50, the full-azimuthing drive can work in conjunction with the tug’s 850-rpm 20-cylinder 645E5 EMD main engine and its steerable-nozzle single screw to give the ATB unit better handling power and precision than a twin-screw tug.

Image Credit: Alan Haig-Brown


Seaspan Challenger and its barge, Coastal Spirit, on the Fraser River.

Protected by a log guard, the z-drive extends an additional 10 feet below the 11-foot draft of the barge. Capt. Robert Ingalls is a third-generation British Columbia coast master and has spent 30 years operating tugs and log ships along the West Coast. Now he puts in a 12-hour shift on Challenger and sleeps in his own bed each day or night, depending on which shift he works.

This past August he was doing the night watch, so he would arrive at the boat at 1800 hours, as the trailers were being offloaded by tractors. The tug is not equipped or crewed to carry passengers, so most of the vehicles are trailers only. The offload and load operation went quickly and smoothly, with Mate Willie Blomke and deck hand Colin Murray directing traffic on the floating parking lot.

By 2035 the last of the new trailers were aboard and Ingalls idled ahead on the main with the azimuthing bow thruster on standby. This gave the crew time to let go the lines and for the slip tender to lift the loading ramp and the doughnut that fits over a large pin on the barge’s bow. A video monitor and walkie-talkie directions from Blomke helped the crew coordinate the activity.

With the vessel freed from shore, Ingalls engaged the bow thruster with the main idling ahead at 366 rpm, less than half of its 842-rpm sea speed. Then he pushed back with the bow thruster at 1,577, well short of its 1,800-rpm rating. The slip sits at a 30° angle to the shore. With the tide just starting to ebb, the river current was less than 2 knots. Pushing from the bow against the main engine, Ingalls let the ATB ease back into the river. Once clear of the slip, he turned the bow thruster to push the bow out from the shore. Then with the vessel well into the stream, he eased downriver about 100 yards to a point where he could turn the bow thruster to effect a 90° starboard rudder to swing the bow around 180° while clearing a midstream buoy. At the same time, he turned the steerable nozzle on the tug to give a 20° to 30° port rudder to stop the stern’s swing. The whole vessel turned neatly on a pivot point just aft of center. Within minutes of clearing the slip, Challenger and her barge were headed downriver.

Image Credit: Alan Haig-Brown


Capt. Robert Ingalls.

It is 12 miles from the loading slip to the “lightship” (the original lightship is no more, and for the past 50 years its role has been performed by various lights on pilings) that marks the end of the river jetty and the drop-off to the Gulf of Georgia. The vessel traffic management system reported several downbound fishing boats and tugs with tows as well as a limited salmon gillnet fishery and the dredge Fraser Titan all working over that distance.

“We’ll just ease back and follow the traffic around the bend,” Ingalls said.

When the river opened up ahead, he pushed on the throttle of the big EMD with the bow thruster helping along, and he passed a tug with a tandem tow. A tug up ahead reported to vessel traffic management that a bunch of kids in a speed boat were towing a water skier back and forth across the traffic lanes. It was comforting to have that bow thruster up there for this bane of commercial traffic.

Across the flat delta lands to the north, the coastal mountains stood out black against the reflected sunset that marked Vancouver Island’s mountains to the west. Challenger was bearing 292° toward the sunset. As the river traffic floated on liquid amber, the conditions were perfect for an evening of watchkeeping stories.

“It isn’t always like this,” Ingalls said. “Sometimes there is a lot of traffic and some deep-sea ships heading up to the Fraser-Surrey docks. Throw in some fog, and you just have to ease right back and follow the traffic out of the river. You don’t get old by being a fool.”

Blomke waved to the cook on the dredge working its way upriver. He had sailed with her on another boat and told of her great cooking. The coast marine community in British Columbia is relatively small, and everyone knows all of the boats and many of the crews, so there is a constant thread of reminiscence of who sailed with whom and who has retired or died — the kinds of things that matter in a tight-knit community. But it is also a shrinking community. The declining forest industry has been the backbone of the towboat industry. These days, moving-truck trailers for expanding populations is one of the few growth areas.

Image Credit: Alan Haig-Brown


Derek Georgeson stands beside the barge’s z-drive, which is powered by a 1,800-hp Cummins diesel.

Coastal Spirit is the second barge built by Seaspan to the same basic design. The first was wrecked when heavy seas from a record-breaking winter storm tore it from a coupling system that held Seaspan Challenger in the notch. (Spirit employs a different coupling system.) The new barge was built in China. On arrival it went to Vancouver Shipyards, a company associated with Seaspan. There the new barge had sets of solid steel pads welded into place in the stern notch. Each of the port and starboard pads has three vertically distributed 1-foot 4-inch receptor holes for the air-over-hydraulic pins that had been retrofitted on Seaspan Challenger in place of the earlier friction system. Now the Finnish-built Acomarin Engineering Jak-400 ATB system provides a powerful positive lock for the articulated tug and barge.

The new barge, at 456 by 82 feet, is also beamier than the original, increasing its carrying capacity to 54 of the 45-foot truck trailers. A tanker barge dramatically changes its draft while loading, forcing its tug to come out of the notch. That’s unnecessary for Seaspan Challenger. With a tons-per-inch (TPI) immersion factor of 60, ballast tanks in the barge hull can be used to accommodate any draft changes. Like the original barge, the bow thruster, electrical auxiliaries and ballast pumps are controlled through an umbilical cord linking the tug and barge. Unlike the first barge, Coastal Spirit has a radio-controlled remote that will allow the bow thruster’s z-drive to turn 90° to port or starboard as well as straight aft. In an emergency, should the barge be separated from the tug, this remote will allow the bow thruster to hold the barge off the shore.

Additional safety features include a towline permanently made up to the tug’s stern winch. This cable passes through the towing pins and is tacked to the starboard bulwarks. It then passes around the bow and down the port bulwarks of the tug before passing over to the barge stern. There it continues up the port bulwarks to a towing rig on the barge’s bow. There is also an anchor on the barge that can be released by hooking and pulling a painter from the tug.

The river jetty curves southward so that the tug was bearing 236° as it reached the lightship. Once clear of the lightship at the river mouth, Ingalls again used the bow thruster to swing the bow of the barge to a 295° heading to take it to the Vancouver Island port of Nanaimo. Using a 20° starboard rudder and three-quarter speed on the main engine and 30° starboard rudder at 1,400 rpm on the bow thruster, the turn was smooth, with none of the vibration one would expect from a single-screw or even a twin-screw tug swinging a 454-foot barge.

For the 27 miles across the Gulf of Georgia to Nanaimo, the tug relied on the main engine at 842 rpm to push. Keeping the bow thruster turning at 1,200 rpm added about half a knot to the speed.

Ingalls likes to keep it on when unpredictable craft such as fishing and pleasure boats are in the area. In winter storms, wind and tide can kick up some big seas in the gulf. This doesn’t present a problem for the ATB, since the 116-inch-diameter pins in the Jak system are fully capable of handling the stresses. However, trips are delayed on occasion for the safety of the cargo. While the ATB can handle the most severe weather, the trailers are a limiting factor in heavy seas.

Approaching Nanaimo at 2330, Ingalls slowed the main engine and used the bow thruster to swing the bow as he passed astern of a yacht. By 0015 the ATB was working its way into the Nanaimo slip. With the main turning at 366 rpm and the thruster at 1,430, the vessels slowed to 1.4 knots with 100 feet separating the bow from the shore ramp. By the time the closed-circuit video monitor showed a 5-foot gap between the shore and barge, the GPS was showing a speed of 0.1 knots. Moments later a gentle nudge affirmed the landing.

By 0145 the tractors had taken all the trailers off and replaced them with a return set. Using a maneuver similar to the one he executed in the Fraser River, Ingalls had the tug and barge turned and heading back out into the Gulf of Georgia for the return run.

This sort of milk run is repeated hundreds of times per day in various waters around the world; but few operators have developed such a smooth system for mating an old single-screw design with state-of-the-art azimuthing engineering.

As the tug and barge headed back through the darkness of the gulf, a bright Venus balanced the light of a quarter moon, just as the bow thruster played against the tug’s main engine. Up in the wheelhouse, the talk moved from the good old days to the future of the towboat industry. On one point, everyone seemed to agree: The future will go to those willing to continue the type of innovation that has made British Columbia a leader in tugboat design and application.

Categories: Maritime News