Newest Z-Tech escort tugs offer smaller footprint and plenty of horsepowerJun 30, 2016 03:02 PM
Triton (left) and H. Douglas M assisting the 797-foot Aframax tanker Garibaldi Spirit in the Houston Ship Channel. The tugs are the first of eight Z-Tech tugs built at Eastern Shipbuilding for G&H Towing, the operating company for Suderman & Young Towing and Bay-Houston Towing.
There were seven azimuthing stern drive (ASD) tugs under construction during a recent visit to Eastern Shipbuilding’s Nelson Street yard, and all were destined for G&H Towing, the operating company for Suderman & Young Towing and Bay-Houston Towing.
Suderman & Young accepted delivery of the first boat, Triton, in December 2015. Two months later, the second tug, H. Douglas M, was delivered to Bay-Houston Towing.
Meanwhile, there were house modules, skegs and other prefabricated units taking shape for the other six vessels in the class, filling the voids among all of the tug hulls under construction at Eastern’s Panama City, Fla., yard.
Keeping track of it all is Mike Nigro, vice president of engineering for G&H. Nigro has supervised a steady fleet-building program since 1994, including the conventional tug Haden II and several ASD tugs, beginning with Matthew K and Jess Newton in 2000. He has worked extensively with Robert Allan Ltd. to build eight Z-Tech 7500-class tugs and the first two Z-Tech 2400 class tugs, Chloe K for Bay-Houston Towing and Zeus for Suderman & Young.
Capt. Nicoli Payne aboard Triton.
The 2400-class tugs are the forerunners of Triton, H. Douglas M and the six other vessels planned in the coming years for G&H, of Galveston, Texas.
A Z-Tech tug’s class is determined by its bollard pull in metric tons; a bollard pull of 75 tons places it in the 7500 class, and so on. However, in the 2400 series, the relationship is to the tug’s 24-meter length. The 7500s have an operating draft of 17 feet, compared to 16.2 feet on the 2400s. The 2400s also are 18 feet shorter than the 7500s.
For Chloe K and Zeus, Nigro collaborated with Robert Allan’s Vancouver firm to scale down the 7500 design and took ideas from other Z-Tech class tugs to create the 2400.
The Z-Tech design incorporates the best characteristics of a true tractor tug and an ASD tug. The heavily fendered bow has a flat sheer leading to a house located well aft and inboard to facilitate close work under the extreme flare common on modern ships.
Triton and H. Douglas M are powered by twin Caterpillar 3516C Tier 3 main engines.
“We also sloped the bulwarks back and lowered the bulwark 4 inches to provide better access under the flare of the ships,” Nigro said. “And the exhaust stacks have been moved inboard and aft of the wheelhouse in comparison to the 7500 class.”
The Z-Tech boats have one hawser winch on the bow, the tug’s working end. During transit and when towing stern-first, tractor tug mode is adopted. To ensure good sea-keeping capability while transiting stern-first, the tug has a “seagoing” stern, which has a strong vertical sheer and is well rounded. As with all ASD tugs, the Z-Tech has omnidirectional speed and the bollard pull is comparable pulling forward or astern.
Much of the 18 feet cut from the larger tug design occurred at the bow of the 80-foot 2400 class, robbing space dedicated to the huge Markey winch fit on the 7500s. Markey designed the DEPCF-48S, 50-hp electric hawser winch for the 2400 class, based on specifications for 60 metric tons of bollard pull, versus 75 tons on the 7500s.
The current version of the DEPCF-48S incorporates Markey’s “NexGen” controls that allow for hands-free operation. A single push-button toggles between the automatic Markey render/recover for maneuvering and setting the brake. A new automatic power-assisted freewheel mode provides limited braking of drum motion while freewheeling, and operates the clutch automatically according to drum speed. Tethered higher-speed tug maneuvers can be undertaken without manually having to clutch out and clutch back in.
Triton chief engineer Troy Freudenburg making a log entry in the tug’s spacious engine room.
An innovation borrowed from G&H’s 7500 Z-Techs is a tripod-shaped dry-docking skeg located aft of the large skeg and forward of each z-drive. The configuration supports the tug in dry dock, saving labor and cost. A second benefit is that the guards protect the z-drives from damage.
Steve Huttman, G&H’s vice president of operations, said the smaller tugs are a very handy size for working in the Texas ports of Houston, Galveston, Texas City, Freeport and Corpus Christi.
“The ship channels are not getting any bigger, but some of the ships are,” he said. “It’s a versatile tug with a smaller footprint, excellent power and all the advantages of the Z-Tech design.”
Extensive electronic monitoring of the 7500 class revealed that the big tugs perform at between 4,000 to 5,000 hp most of the time. “Performance-wise, the smaller tugs were designed to hit the sweet spot,” said Huttman. “They are ideal for assisting the small and mid-sized ships, but also have enough horsepower and indirect towing capability to work the larger ships. The 2400 class complements the 7500s, which are able to assist the largest ships calling in our ports.”
Markey DEPCF-48S 50-hp electric hawser winch on the bow of Triton and H. Douglas M.
The 2400-class propulsion train consists of two Caterpillar 3516C, Tier 3 main engines at 2,575 hp each, and Schottel SRP 1215 z-drives with 94-inch outboard rotating propellers in nozzles.
Schuyler Companies supplied the cylindrical fender to wrap the curve of the bow bulwark. Below the bow fender, a section of extruded D rubber is installed to protect the lower section of the bow and the forward end of the skeg. A cylindrical fender also protects the stern. The lower bow and side shell are covered with SR3D double-loop fendering. The bitt fenders, usually the first to show wear, can be removed for maintenance and repairs.
Despite the shorter length, the 2400s are only a foot less in beam, creating a deceptively spacious interior. The carpenters and joiners at Eastern custom-built all of the interior cabinets and furniture using oak and South American cedar. The stateroom layouts are shipshape and the cabinetry displays fine craft and care.
“We utilized all of the usable space in the voids for storage,” Nigro said. Finished cabinets have been installed between the frames anywhere that there is an accessible expanse. The HVAC system and the winch controls have been fit in between structural framing in the lower common area.
Twin Schottel SRP 1215 z-drives installed on Triton and H. Douglas M.
In addition to Triton and H. Douglas M, Neptune, the third tug in the series, is under construction at Eastern for Suderman & Young, followed by Zyana K and David B, both for Bay-Houston. Oceanus for Suderman & Young, Laura B for Bay-Houston and, finally, Poseidon for Suderman & Young also are in the works.
“We see this size of vessel as being able to work in all of our ports,” Huttman said. “It’s a handy-sized tug with the right mix of speed and horsepower for our marketplace.”
To prove the point, Chloe K and Zeus have recently been relocated from the Houston Ship Channel to the Port of Corpus Christi, where, according to Huttman, the vessels are performing admirably.