Signet Maritime has been more than happy with the highly maneuverable and efficient Signet Weatherly built at itsMississippi yard in 2012. The 4,720-hp Robert Allan Ltd. RAmparts 3200-class ocean towing and escort tug and its 61 MT of bollard pull have exceeded expectations.
So when Signet wanted to build new multimission tugs that could handle big ocean towing jobs, they decided to base it on the Weatherly’s successful design but make it more powerful.
The result is a pair of multimission 6,834-hp tugs built for the Houston-based tug operator by Patti Marine Enterprises at its Pensacola, Fla., shipyard. The 105'×38'×17'8" RAL-designed tugs are the seventh and eighth RAL designs for Signet. The first tug, the Signet Arcturus, was delivered in April. The second, the Signet Polaris, was delivered in June.
Signet essentially took the hull of the similar-sized 105'×38' Weatherly that is outfitted with MTU 16V4000 M60 engines and Niigata Z-drives and swapped in Caterpillar engines with Rolls-Royce Z-drives.
“We wanted these tugs to work offshore, so they are more powerful with more bollard pull,” said Joe Dahl, vice president and general manager for Signet Shipbuilding & Repair, Pascagoula, Miss. Dahl has essentially been based in Pensacola during the construction of the tugs.
Bigger engine rooms were needed to fit the Caterpillar C175-16 Tier 3 engines, each rated at 3,417 hp. The Cats drive Rolls-Royce US 255 controllable-pitch Z-drives, and a pair of 110"-dia. 4-bladed nibral wheels in Kort nozzles. The package gives the tugs a hefty 83.45 tons of bollard pull ahead and 75 tons astern.
For service power, the tugs are outfitted with pairs of John Deere 6068AFM85-powered, 125-kW generators.
Many of the new tugs’ features are not typically found on other ABS-classed tugs. What sets these tugs apart are the additional requirements needed to secure a Coast Guard Subchapter I Certificate of Inspection.
Patti Marine project manager Ashley Stone said the Arcturus and Polaris are the first Subchapter I tugs in this size range. Usually, Subchapter I tugs are much larger. The Arcturus and Polaris are the also the first RAL RAmparts tugs to receive Subchapter I certification.
“It is a very small vessel to have this classification,” said Stone. “The tugs have automation, a safe manning certificate, and a lot of SOLAS features that bigger tugs have.”
Subchapter I tugs are rare, he said. The only other Sub I tugs he’s aware of are Crowley Maritime’s 10,880-hp Ocean-class tugs that have 150 MT of bollard pull. Two 146'×46' and two 156'×46' Ocean-class tugs were built at Bollinger Shipyards.
“Having the dual ABS classification and Coast Guard inspection raises the bar for all facets of construction,” said Stone. “With a Coast Guard NVIC 10-82 tug, the higher standard applies, regardless of the system. If an ABS and Coast Guard rule is not the same, then the more stringent of the two is incorporated and enforced. No doubt, this results in increased safety and redundancy for the owner and operators of the tug.” (With NVIC 10-82, the USCG allows ABS to review certain systems for compliance with Subchapter I. It also permits ABS surveyors to perform structural inspections on behalf of the USCG.)
Dahl agreed. “At Signet we’ve always been advanced in our thinking and wanted to provide a safer and better operating vessel that can meet all the requirements of our customers. By being U.S. Coast Guard inspected, we exceed our competition in certifications and provide our customers with more skilled licensed personnel. The chances of something going wrong with our vessels are far less than others.”
To meet Subchapter I, the tugs have a 400-point alarm and automation system, with automatic starting and remote monitoring of the fire pump. The automation system was reviewed by the Coast Guard Marine Safety Center and extended trials were required to test the system. The system allows for reduced manning.
For ship-assist work, each tug has a Markey DEPCF-52S electric hawser winch on the bow. For ocean towing and rig moves, the tugs have a Markey TESD-34 100-hp double-drum electric towing winch on the stern.
Signet determined that the combination of a bow hawser and a stern towing winch would give them the most flexibility to meet customer needs. This meant that the design needed to incorporate a large bow for the hawser winch.
A Coastal Marine Equipment capstan was also added to the main deck bow for mooring line assistance.
The hawser winch has 500' of 9"-circ. Samson Saturn-12 line and the big towing winch — for rig moves and ocean towing — has 2.25"×2,500' tow wire on one drum and 2.25"×1,500' wire on the other.
Stone pointed out that typical escort/ship-assist tugs have much smaller fuel oil tankage. With the tugs’ dual ocean towing configuration, Signet decided to increase the fuel oil tank sizes to increase tug endurance. Each tug has tankage for 90,068 gals. of fuel oil.
Other notable changes/additions from the Weatherly was the addition of a control room so the tugs have full monitoring and control. Also, the new tugs are FiFi 1 classed. The FiFi 1 classification was needed so the tugs can work LNG tankers.
A typical ABS-classed tug will have two smaller, dual-purpose fire main/bilge pumps.
The Arcturus and Polaris each have a high output, dedicated fire main pump and two higher capacity bilge/pumps, for redundancy. The FiFi 1 system features two FFS SFP pumps, driven off the front of the main engines, and two FFS 1200LB remotely operated monitors. The pumping capacity is 5,300 gpm with a range of 400'.
Other important additions include an independent engineers control room, which was added to the forward end of the engine room. To enhance crew safety, Signet added a bridge navigation watch alarm system. The wheelhouse arrangement was also modified to incorporate a built-in GMDSS console and aft control station. Also added was a stern steering station in the wheelhouse, which overlooks the aft deck and winch. It was completely outfitted with communications and fully functional engine, Z-drive, towing and FiFi controls.
The Signet Arcturus recently completed its first big job, towing Chevron’s Big Foot deepwater platform. The tug reportedly outperformed bollard pull estimates. The ASD tugs operate out of Ingleside, Texas, where they primarily perform offshore and inshore rig escort, barge and subsea support work.
Signet has built and is operating more RAL tugs than any other company in the U.S., according to Stone. Based on this experience, Signet went into the design process with the intention of building a tug with the most desirable features possible. With the Arcturus and Polaris, that’s what they got — two desirable tugs.