Signet’s two newest z-drives to provide LNG escort services


Signet Maritime Corp. has taken delivery of two new identical z-drive tugs, Signet Constellation and Signet Stars & Stripes.

The tugs — 100 feet long with a beam of 40 feet — provide terminal support and escort services to Angola LNG Supply Services (ALSS) in the Port of Pascagoula, Miss., and will assist LNG tankers, oil tankers and cargo vessels calling at the LNG, oil refinery and other dry cargo terminals in the port. The tugs were built in Gulfport, Miss., by Trinity Offshore LLC.
Designed by Robert Allan Ltd., the RAstar 3100 escort tugs are the newest and most sophisticated vessels to join the Signet Maritime fleet. When moving ahead, the tugs have demonstrated a bollard pull of 81.3 metric tons.

Its 110.2-inch controllable-pitch four-blade nibral propellers are housed in Kort nozzles.

“I studied the engineering needs of our customer to build a superior machine for this specific project,” said Signet Maritime President J. Barry Snyder. “A team of technically advanced professionals was commissioned to develop a comprehensive plan to enhance safety and increase efficiency of the marine services required to support ALSS in Pascagoula. We are grateful to Robert Allan Ltd., naval architects, for their support to develop the RAstar 3100 class tugs.”

The tug’s RAstar hull form is a proven design and incorporates a significant forward flare on the upper hull sides. When the tug heels over due to towline influence during an escort operation, the weather sponson is submerged, allowing the generation of a significant “righting” force to maximize stability. The hull also incorporates a large foil-shaped skeg complemented by a 2.25-inch furnace steel soleplate, providing dramatic reductions in roll amplitude and accelerations.

Signet has a long relationship with the designer, having contracted with Robert Allan for the design of its AZ-30/80 class ASD tugs America and Pacific Star, which were delivered in 2009, and a RAmparts 3200 tug, Signet Weatherly, currently under construction at Signet’s shipyard in Pascagoula and scheduled for delivery in February 2012.

“Signet worked closely with Robert Allan to design and engineer a vessel that offers superior ship-handling, escort, and sea-keeping performance and incorporates cutting edge technology far above the typical conventional designs,” said Kristie Eager, Signet’s senior manager of contracts, administration and corporate governance.

Eager noted that Signet has a history of naming its vessels after sailboats that have won the America’s Cup.

Constellation was the winner of the 1964 America’s Cup over Sovereign, and Stars & Stripes was the winner in 1987 over Kookaburra III.

Eager said that the names of the sailboats were chosen “based on their strong, tough performances.”

One of the two EPA Tier III CAT C175 ACERT 16-cylinder main propulsion diesel engines delivering 3,417 hp each.

“Owing to these namesakes, the new tugs will be proud warriors, serving our customers well with a higher standard than ever before,” she said.

The tugs feature accommodations for six people in four staterooms. The mess area includes a full-entertainment center and sideboard. The galley is equipped with quality commercial appliances and counters and cupboards finished in brushed stainless steel.

Both vessels were built entirely under cover at Trinity Offshore’s 60-acre facility in Gulfport, using only U.S. forged steel with all fittings, machinery and engines of U.S. construction. The only non-U.S. machinery were the z-drives, which were built in Finland.

The RAstar 3100 tugs are powered by two EPA Tier 3 Caterpillar C175 ACERT 16-cylinder main propulsion diesel engines delivering 6,834 hp. The engines drive twin Rolls-Royce model US255 z-drives, with two controllable-pitch 110.2-inch nibral four-blade propellers in Kort nozzels.

The engines feature a combination of advanced electronics/monitoring systems, increased engine efficiencies through computer-aided design, and modernized common rail fuel injection systems resulting in lower emissions, improved performance and reduced fuel consumption.

For auxiliary power the tugs each have three John Deere model 6068TFM76 diesel gensets capable of producing 99 kW each.

The tugs have side-by-side Markey Machinery double-drum render/recover hawser winches for use in highly dynamic ship-assist and escort applications. The winches were designed and built by Markey specifically for the RAstar 3100 series tugs. The winches feature a 200-hp AC variable-frequency electric drive and a space-maximizing all-above-deck compact gearbox. The DESDF-48 is capable of line pulls up to 625,000 pounds and line-speeds up to 780 feet per minute.

The wheelhouse has a cockpit-style control console, pilot chair on a sliding track, chart table, log desk and controls, instrumentation and navigation aids.

Wheelhouse electronics include two JRC JMA-5200 radars with two KEP Marine KEPC15 15-inch displays, a laptop computer for electronic chart display, a JRC JLR-20 compass, JRC JHS-182 AIS system and Transas Navi-Sailor 4000 navigation software. The vessel has two Icom M504 VHF radios.

The Markey DESDF-48 200-hp winch is capable of line pulls of up to 625,000 pounds.

The tug is equipped with three types of fendering systems — W-type, D-type and Shibata cylindrical fendering supplied by Schuyler Co. of Broussard, La.

For firefighting each vessel has two FFS pumps, model SFP 250×350 that run off the front of the main engines. Monitors are remote-controlled dual FFS model 1200LB, each delivering 10,570 gpm with a range of 400 feet.

For hawsers, the boats carry two Samson Saturn-12 lines that are 9 inches in circumference and 600 feet in length.

There is also a Burrard Iron Works CE4B electric capstan in the stern.

With launch of the two new tugs, Signet showed its optimism about business in the Gulf. “Signet is extremely bullish on our outlook for cargo, rig support and offshore services in the Gulf of Mexico, including bringing a higher level of quality and safety to LNG vessel operations and technologically advanced vessels owing to the changing laws, environmental concerns and specific LNG demands,” Eagers said.

By Professional Mariner Staff