LNG harbor tug
Naval architect and design firm Robert Allan is actively working on its z-drive LNG harbor tug. Jim Hyslop, manager, project development, said that the main feature is placing the crew quarters on the aft deck to make enough room for the LNG tanks. “This is suitable for a harbor tug but not for a towing tug because the crew accommodation has taken up that space and there is no aft winch.” Officially known as the 3600 RANGLer class — Robert Allan’s Natural Gas (Liquefied) — the vessel is being offered in a single-fuel option.
Hyslop said the project is still under development and a decision has yet to be made on manufacture.
In a news release, the firm says: “On many tugs today, especially those dedicated to terminal support or escort towing, the aft deck is essentially redundant. A well-designed modern terminal tug should be able to tow and maneuver equally well going in either direction, hence has no need for an aft winch. The aft deck space on many tugs is thus often just a large empty area. We considered this to be prime real estate for locating the accommodation facilities displaced by the LNG tanks.”
Bureau Veritas (BV) and the American Bureau of Shipping (ABS) have both given approval in principle. Length overall is 36 meters, power is from two 2,430-kW motors, and LNG gross capacity is 80 cubic meters. Predicted speed is 14 knots with a bollard pull ahead of 80 metric tons.
Robert Allan said, “Departing from ‘traditional’ diesel tug designs, the RANGLer deckhouse is biased aft to provide excellent visibility from the wheelhouse and an efficient working deck forward.”
LNG inland towboat
Conrad Shipyard is offering a 4,200-hp, z-drive, LNG inland towboat option. Designed in conjunction with The Shearer Group, the boat has been given approval in principle by the American Bureau of Shipping. The engine is based on Wartsila dual-fuel engine technology, but not wedded to it, according to The Shearer Group.
V-Pod diesel electric
Eastern Shipbuilding says the development of its “Thunderbolt” diesel electric, V-Pod towboat design heralds a new era for inland waterway towboats as dramatically as the introduction of conventional z-drives a few years ago. More than a year has been spent on the design in conjunction with Gilbert Associates.
The Panama City, Fla., company says the that the most revolutionary features of the 4,200-hp, 120-foot boat are the incorporation of diesel electric propulsion with twin Verhaar Omega 690VAC electric V-Pod propulsion units with twin Omega Propulsion AFE/VFD drives, plus a highly programmable power management control. “The propulsion motor is in the lower unit, rather than a pair of diesel engines above the main deck in the steering compartment as in conventional z-drive towboats,” said Stephen Berthold, Eastern’s vice president of sales and marketing. “The prop is attached directly to the propulsion electric motor, making the propulsion efficiency extremely high because you don’t have the mechanical power loss in the mechanical drivetrain.”
An artist’s rendering of the LNG towboat being developed by Conrad Industries and The Shearer Group.
Bristol Harbor Group
Steering comes from redundant twin motors for each unit. The V-Pod has continuous 360-degree rotation and 180 degrees is achieved within 14 seconds. The biggest advantage, said Berthold, is that the propulsion electric motor is completely reversible and variable in speed in both directions. “You get a floating object stuck in the nozzle of a conventional z-drive and what are you going to need — a diver to get it out, or it’s off to the shipyard. The V-Pod can reverse the propeller and spit it out.”
The power management system, provided by Beier Radio, works through the IEM Marine switchboard with load-sharing capabilities. The system is designed to allow the operator to have full control of the three Cummins AVK DSG-74 water-cooled generators, supplying 990 kW, 690 VAC at 1,800 rpm.
“The system is programmed to the owner/operator requirements, with automated generator start/stop features or the pilot’s manual power management from the pilothouse as needed,” said Berthold. “If the pilot knows there’s a nasty bend or heavy traffic in the river a quarter-mile ahead but the power management system indicates it wants to shut down one generator, he can keep all three generators online and make the maneuver safely.”
Each of the three 690 VAC generators is powered by a Cummins QSK38-DM diesel engine. Each engine is a 38-liter, EPA Tier 3, 1,400-hp V-12 rated at 1,800 rpm. There is also a Cummins 90-kW air-cooled harbor generator for dockside use, reducing fuel consumption and cutting emissions.
Redundancy is built in, in spades. “Half the paralleling switchboard can go offline and you will still have power and twin propulsion control. Lose a generator engine or one AFE/VFD drive, and the pilot still has twin propulsion with 78 percent thrust and control versus 50 percent,” said Berthold. The vessel has 100 percent redundant low-voltage transformers for ship service power.
Fuel consumption in principle will be reduced by 8 to 10 percent compared to a traditional propulsion towboat. “But it depends on the pilots and how much they allow the power management system to control the generator power/load requirements while underway,” said Berthold.
He said there has been definite interest. “Looking back at z-drive propulsion here in the U.S., it took 20 to 25 years to migrate from the U.S. offshore industry and be finally accepted by the inland operators. Offering this Thunderbolt design in an LNG inland towboat option is the next step in the inland marine industry’s growth.”