Containerships and tankers calling U.S. ports are getting bigger. By necessity, tugboats that handle these massive ships are growing, too.
Mark E. Kuebler is the first of five Tier 4 tugs built for Bay-Houston Towing Co. of Houston. Gulf Island Shipyards is building the series at its Jennings, La., yard based on the new Z-Tech 30-80 design from Robert Allan Ltd. of Vancouver, B.C.
Philip Kuebler is president of Bay-Houston Towing Co. and son of the vessel’s namesake. He cited an increased need for larger tugs capable of escorting and assisting neo-Panamax containerships and very large crude carrier (VLCC) tankers. VLCCs can reach 1,500 feet long and 200 feet wide.
“Just a few short years ago, before the export ban was lifted, refined products were leaving our ports in smaller vessels,” he said. “Now, larger tankers are loading, and the demand for greater-sized tugs has increased. We already had multiple 75-ton tugs available but needed additional large high-performance escort tugs to serve our customers’ increasing needs.”
Mark E. Kuebler Capt. Bobby Pytka discusses the next ship move with mate Nicholas Schiaffino.
Bay-Houston provides ship-assist and escort services in Houston, Galveston, Freeport, Texas City and Corpus Christi. The company’s remaining four Z-Tech 30-80s, expected within the next year from Gulf Island, will be parceled out to meet the demands at these ports. The lead tug is named for Bay-Houston’s chairman.
Bay-Houston put Mark E. Kuebler to work in Corpus Christi, Texas, almost immediately after delivery in mid-December 2018. Escorting and assisting the first VLCC to load at the Texas port was one of its first jobs.
The Robert Allan 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. The stacks are inboard, aft of the house, also for better access under the flare, while the bulwarks are sloped back and lowered.
Propulsion aboard Mark E. Kuebler comes from twin Tier 4 Cat 3516E mains generating 3,386 hp each.
The Z-Tech boats have a hawser winch on the bow, the tug’s working end. During transit and when towing stern-first, tractor tug mode is adopted. The tug has a “seagoing” stern, which is well rounded with a strong vertical sheer for good sea-keeping while transiting stern-first.
Bay-Houston equipped its Z-Tech 30-80s with twin Caterpillar 3516E Tier 4 mains generating 6,772 hp at 1,800 rpm. The engines are coupled to Lufkin MV1600S marine gears at a 2:1 reduction, driving Schottel SRP 510 FP z-drives with 110-inch propellers. Bollard pull is 81.5 metric tons.
The engines’ SCR system, designed to reduce NOx in engine exhaust emissions, consists of a catalytic converter paired with each engine and tankage for 2,134 gallons of diesel exhaust fluid (DEF). The sheer size of the additional equipment required for Tier 4 called for some reconfiguring in the engine room.
The machinery space consists of two John Deere 125-kW gensets port and starboard, centered by two Caterpillar C18 engines each driving an FFS 6,200-gpm fire pump. Each fire pump has foam proportioner valves for foam capability with the ship’s firefighting system. Two FFS monitors are located on the upper deck forward of the house, with the whole arrangement combining to earn the tug an FFV1 certification. Next in line are the two main engines shafted to the azimuthing drives.
The four-person crew consists of, from left, AB Landon Walters, chief engineer Jake Beauchamp, mate Nicholas Schiaffino and Capt. Bobby Pytka.
Robert Allan Ltd. determined through computer modeling that adding sponsons to the hull would improve escort performance. Those tests demonstrated that more than 100 metric tons of steering force would be generated at 10 knots with a 98-foot ASD tug — a particularly important feature when escorting big ships.
“The sponsons are placed on the upper portion of the hull sides and continue along the majority of the hull longitudinally,” said Xuhui “Bill” Hu, project director at Robert Allan Ltd.
The firm developed the unique sponson hull form specifically for escorting large vessels in environmentally sensitive areas. The sponsons enable tugs to generate greater steering and/or braking forces hydrodynamically at 8 to 10 knots, Hu said. The sponsons increased steering force at 10 knots by 18 percent compared to the original design.
Mark E. Kuebler assists the bulker Nassauborg into the terminal in Galveston, Texas.
When a tug performs escort operations, steering and braking forces generate high heeling moments that cause the tug to lose its stability rapidly as the heel angle increases. Sponsons provide the additional buoyancy, righting arm and stability when a tug heels at great angles during escort work, according to Hu.
Changes in Coast Guard and EPA regulations, combined with the increase in ship dimensions since the introduction of the first Z-Tech 30-75 and 24-60 series, influenced the design changes. The new 30-80 tugs built for Bay-Houston meet Coast Guard Subchapter M requirements.
“All these requirements and regulations were not in effect when the previous Z-Tech 30-75 and Z-Tech 24-60 were designed and constructed,” Hu said, referring to earlier vessel classes operated by G&H Towing.
The powerful Markey hawser winch is loaded with 426 feet of Samson Saturn-12 line.
The sponsons add 44 inches to the width of the tug. “They give the tugs greater stability and improve working conditions and safety while also increasing escort performance with the additional reserve buoyancy,” said Kuebler.
Mark E. Kuebler has a Markey electric hawser winch on the bow wound with Samson Rope’s Ultimate Towing System. The arrangement of three 3.25-inch-diameter lines consists of 136 feet of Quantum-12 backer line to take up the friction, 436 feet of Saturn-12 main towing line and a 186-foot Saturn-12 pendant.
Computers and electronic components are coming down in size but, like tugboats, the demand for power seems only to increase. Bay-Houston Towing knows this firsthand. The fifth-generation family business dating back to the late 1800s has been committed to growth and safety as market demands call for bigger, more powerful equipment.
“These new Z-Tech 30-80s are a testament to our commitment to our customers,” Kuebler said. “As the needs of our customers and the ports we serve evolve, we will continue to grow to meet their needs.”