Signet Sirius | Signet Maritime, Houston, Texas
Signet Maritime has developed a powerful and highly capable tugboat series designed specifically to escort and maneuver some of the largest oil tankers on Earth.
The 7,725-hp Signet Sirius and its forthcoming sister vessel, Signet Capella, were built using the Robert Allan Ltd. Advanced Rotortug (ART) design. The platform features three azimuthing drives, which provide unparalleled maneuverability and indirect towing abilities. With 92 metric tons of bollard pull, the two tugs are the most powerful ARTs in the world.
They’re also the first tugboats with EPA Tier 4-rated engines in the Signet fleet, and the first tugs in the United States with CyberSecurity-1 and Enviro notations from ABS. Signet Sirius also was the first U.S. tug developed using a 3D design process.
Since its delivery in late 2023 from Signet Shipbuilding & Repair (SS&R) in Pascagoula, Miss., Sirius has operated at the Enbridge Ingleside Energy Center in Ingleside, Texas. It is the largest crude export terminal in the country by volume, and one that regularly hosts the mammoth tankers known as very large crude carriers (VLCCs). Capella’s arrival later this year will give Signet additional capabilities at the South Texas terminal.
“The ART was specifically designed to exceed the needs of the Port of Corpus Christi and safely and efficiently perform the duties expected of her. Everything from the hull design to the propulsion package to the winch was designed with this specific task in mind,” according to J. Barry Snyder, president and CEO of Signet Maritime.
Signet Maritime is based in Houston, Texas. The company’s tugs perform ship-assist work in Brownsville, at the Texas-Mexico border and in Corpus Christi, along with Pascagoula. It also has robust offshore towing capabilities with the 12,500-hp Signet Warhorse 1 and Signet Warhorse 2.
Planning for Signet Sirius and Signet Capella began in the late 2010s as the Port of Corpus Christi embarked on a dredging project to deepen its ship channel to 58 feet. Signet worked Robert Allan Ltd. naval architects to develop a tugboat that could effectively work these deep-draft VLCCs. The team used advanced simulations and computational fluid dynamics to determine the best overall tugboat platform. Those detailed studies proved the ART was the best tug for the job.
“The ART design is the first in the region to incorporate its unique three-thruster design, which allows for significantly more maneuverability, power and control while being able to exert forces in vectors that are not possible with a traditional two-thruster design,” Snyder said.
“The ART can provide affect to the ship in scenarios that are not possible with a typical [azimuthing stern drive tugboat], as the potential force vectors are significantly increased,” he added. “The ART can perform advanced maneuvers without sacrificing thrust or power while maintaining continuous line tension.”
The ART concept developed in Europe a generation ago. Robert Allan Ltd. ultimately partnered with Rotortug B.V. of the Netherlands and helped refine the design, Robert Allan, the firm’s executive chairman, told Professional Mariner in 2017. Seabulk built the first ART on American shores in 2017 and added four more to its fleet over the next six years.
Signet’s 92-32 ART class represents 92 metric tons of bollard pull in a 32-meter envelope. The tugs feature three z-drives in a triangular configuration with two forward and one aft along the centerline. The tug can generate 107 tons of steering force and 157 tons of braking force, ensuring full redundancy in escort capabilities as well as optimal maneuverability and control, according to James McCarthy, the Robert Allan Ltd. project director for the Signet tugs.
“A sponsoned hull form provides additional stability, which is critical for high-power escort operations,” he said. “A powerful Render/Recover winch, with performance capabilities sufficient to match the high line tensions achieved during tethered indirect maneuvers and with performance tuned to match the tug’s seakeeping characteristics, along with a specially designed staple, enhances escort performance.
“The inclusion of a new lightweight fendering system and chemically strengthened windows underscores the tug’s focus on weight reduction and performance capabilities,” McCarthy continued.
Signet assigned Capt. Edward Pearson to Sirius. Pearson has 40 years of maritime experience, with 36 of those years spent working in the wheelhouse. The first half of his career was spent running barge tows between Brownsville, Texas, and Mobile, Ala., and points between. He started working for Signet almost by accident, as he recalled, when looking for part-time work.
Since then, he has traveled around the world with Signet, most recently to Rotterdam to learn the fundamentals of Rotortug operations. Pearson credits that training with giving him the tools to run the vessel the way it was intended.
“The more advanced it gets, the more I like it,” he said. “I am learning new things every day and learning new things about the boat and teaching myself and bettering myself and building on that foundation. Every day is a new trick with this tug.
“It is probably one of the most complicated boats you’ll ever run because of the advanced technology, but it simplifies your job and your ability to do it safely,” he continued.
The geometry of the drives and the ability to maintain constant force on the line is a primary difference between an ART and an azimuthing stern drive (ASD) tugboat. The operator can position the drives in a way that maintains line tension — even during complicated and complex maneuvers. For instance, the tug can swing around the bow or stern of a ship and continue to exert force on the line. Even at 1.5 knots, Sirius can maintain 60 tons of line force, Pearson said. It also can go up to 8 knots sideways, hit 14 knots ahead at full power and spin 360 degrees while maintaining a nearly even keel.
“The more I drive it, the more I like it,” Pearson said as he spun the tug 360 degrees in Corpus Christi Bay, a huge smile on his face. “It is like a big Jet Ski.”
The engine room on Signet Sirius feels massive, despite the third engine and increase in machinery. The two MTU 12V4000 mains are located forward on the port and starboard sides, while the third engine is located aft along the centerline. All three are paired with Kongsberg drives turning 98.5-inch props in nozzles. Electrical power comes from two R.A. Mitchell Co. 300-kW John Deere gensets.
The vessel features a custom Markey Machinery winch package on the bow and stern. Both are 200-hp Class III electric winches spooled with 675 feet of 3.25-inch Samson Saturn-12 towing line. Custom staples are installed fore and aft to place the lines in optimal position for indirect towing maneuvers under aggressive power.
Buoyant Works, which is based in England, supplied the custom fendering package consisting of modular sections that wrap around the hull. The ultra-high-performance polyurethane system weighs roughly 30 percent less than comparable fendering. Each fendering block can be replaced individually, simplifying the process of swapping out fender sections.
Sirius is equipped with a 1,000-kW (1,341-hp) fire pump driven off the port MTU main engine with an integrated foam and deluge system paired with two FFS remote-controlled fire monitors. The tug also has connections that can feed shoreside hoses for firefighting on land.
The wheelhouse features huge floor-to-ceiling windows for excellent visibility, including one looking aft that is the largest-ever window on a Signet tugboat. The electronics package boasts next-generation Furuno components, including radar, AIS and GMDSS. Signet also put extensive effort into hardening the vessel against cyberthreats to earn the ABS CyberSecurity-1 notation.
The typical crew contingent on Sirius is four people, comprising a captain, engineer, mate and deck hand. The vessel has berthing for eight people in four cabins.
The design for Signet Sirius and Signet Capella occurred entirely in 3D for the first time in the U.S. Rather than relying on 2D drawings, which must be updated with each modification, the plans came together using advanced 3D software that could be adjusted and shared with all parties in real time.
“3D design has improved the production methodology and efficiency of our shipyard significantly,” said Hans Schmidt, president of SS&R. “All future vessels constructed at SS&R will follow the same design regimen.”
The vessel design went beyond the regulatory requirements by meeting ABS Enviro and ABS Low Emission Vessel notations. Sirius and Capella also meet intact and damage stability standards for all below-deck watertight spaces. This ensures the tug is survivable for crews in the event of a breach of either the aft or forward thruster rooms or the main engine space.
“Not required by regulation, and difficult to attain on a vessel this size,” Schmidt said, “but critical to Signet’s standards of safety in design.”
He cited the value of close collaboration with Signet’s customers, naval architects at Robert Allan Ltd., Rotortug, Markey Machinery and MTU, among others, for delivering a successful finished product. ABS and the U.S. Coast Guard also were integral partners.
“Close collaboration between the fleet and shipyard, as the same company, has ensured that the design ‘lessons learned’ from the dozens of other vessels in our fleet are applied to this design,” Schmidt said. There are “bespoke solutions throughout to make the boat safer, smarter and more effective, and the crew more comfortable, connected and efficient.” •