Workboat Magazine July '04
more background on Rigdon fleet of diesel-electric PSVs
Boats & Gear
Moving Day
Electrifying
Rigdon Marine goes diesel-electric for its new PSV fleet.
By Max Hardberger, Correspondent
In an example of technology catching up with the past, the first in a series of 210' ´54' diesel-electric platform supply vessels was recently delivered to Rigdon Marine Inc. The vessel is also the first for the new Houston-based offshore service vessel operator.
Built by Bender Shipbuilding & Repair Co. Inc., Mobile, Ala., and designed by Guido Perla & Associates Inc., Seattle, the Orleans has three generators forward, producing up to 4,560kw, and two electric Z-drives aft.
“Diesel-electric drives have been around for decades,” said Richard Currence Jr., Rigdon’s vice-president of operations, “but in the past their advantages were offset by their higher initial cost and higher fuel consumption. Now, with a modern diesel-electric’s fuel consumption substantially lower than a conventional drive’s, its higher initial cost is easier to justify.”
Two stern-mounted Steerprop SP 20 azimuthing Z-drive units driven by two Alconza 2,100-hp variable-frequency AC electric motors provide main propulsion. (The Z-drives turn 92" props.) The motors are directly coupled to eliminate the expense, weight and vibration of shafts.
Currence said the Steerprop Z-drives, manufactured in Sweden, are refinements on the proven Aquamaster design.
THE DP DIFFERENCE
Other offshore supply vessels with diesel-electric drives are already in service, but, according to Currence, the advent of dynamic positioning systems has brought the diesel-electric drive into its own.
DP systems give vessels the ability to standby near an offshore platform for cargo or other operations without the risk and difficulty of a line connection.
“Geared engines, even when connected to Z-drives, can only produce power within specific rpm ranges,” Currence said. “When a vessel is in DP mode, the engine computer has to clutch the engines in and out continually in order to maintain position. Not only is this hard on the drive train, it also causes delays in the vessel’s reaction to commands, degrading her position-keeping ability. By contrast, electric motors provide torque throughout their rpm range, so the Z-drive’s response to command is precise and instantaneous.”
Larry Rigdon, Rigdon Marine’s CEO, added: “There’s another dimension to diesel-electric drive and dynamic positioning. DP-2 requires total redundancy, so that a failed system can be bypassed without loss of control. That kind of redundancy in shaft and gear is expensive to buy and maintain. With diesel-electric, much of the redundancy in the electrical circuits is achieved through duplicate LANs (local area networks) that are cheap to buy and easy to maintain.”
According to Rigdon, the PSVs’ hull lines are derived from a highly successful series of tuna seiners designed by Guido Perla several years ago.
“Tuna seiners need to go out fast and come back heavy,” Rigdon explained. “They’ve always gone out 120 to 150 miles or more. Supply boat designers don’t usually consider the boat’s speed in light condition, but times have changed. The time saved on a light-boat trip means better utilization of the asset.”
Rigdon said that the Orleans has achieved speeds of 13 knots at full load and more than 15 knots light.
“Until recently, platform service vessels only went out a hundred miles or so. Now, with the longer trips involved in servicing deepwater fields, a new hull form was needed. We think this is the hull.”
Rigdon said that the task of fitting the vessel’s machinery and cargo tanks into the speedy lines of a seiner hull was made easier since the generating plant could be located anywhere in the hull. The small size of the electric Z-drive units also provided the cargo bay with more room, allowing placement of the tanks for best trim and stability.
LOWER FUEL BURN
Fitted into the vessel’s compact engine room are two 1,825kw (2,500 hp) generators driven by Cummins QSK 60 engines, and a third 910kw (1,220 hp) generator driven by a Cummins KTA 38 engine. The boat’s Alstom DP system can start and stop any of the diesel engines and bring any or all of the generators online as needed. By analyzing the vessel’s overall power requirements, and by using each diesel engine only within its peak-efficiency rpm range, the Alstom system’s computer can meet given power requirements at the lowest fuel-burn rates.
Rigdon said that the Orleans burns 230 gph at 13 knots fully loaded but only 88 gph at 10 knots, providing fuel savings of up to 10 percent over conventional drives. “The real fuel savings is in DP mode,” he added, “because that’s when shaft drives are least efficient. But even on long voyages, diesel-electric drives save money.”
Rigdon pointed out that another benefit to the reduced fuel-burn is a reduction of noxious emissions produced per ton-mile.
For harbor maneuvering and to assist in DP stationkeeping, the Orleans has two Berg bowthrusters driven by two 1,000-hp electric motors in a thruster room at the bow.
According to Jim Whitley, project manager for Rigdon, the choice of two smaller diameter thrusters over a single, larger thruster was dictated by the redundancy requirements of DP-2 certification, but the smaller tunnels also allowed the designers to fit them into the hulls more efficiently.
“We had Berg design special blades for (the thrusters),” Rigdon added. “Since bowthrusters are in constant use during DP, their noise does affect the crew environment. So we had Berg install special highly skewed blades in the thrusters to reduce noise. Looks like they’re working, because the captain says he has to look at the gauges to see if the thrusters are engaged.”
Another advantage to diesel-electric drives, according to Whitley, is their inherent reliability and the variety of responses available to meet an equipment failure.
“Compared to diesel engines, electric motors are almost failure-free,” said Whitley. “And each of the generators, even the little 910kw generator, can provide all the power the vessel needs, either underway or in DP mode, so the operator has a number of options if a failed component has to be isolated and bypassed.”
Although the primary purpose of moving the house forward was to provide a larger afterdeck, another benefit was more space in the cargo bay underdeck for the dry-material and liquid-mud tanks.
“With the house forward and the generators under the house, we’re able to run power back to the drives with flexible electric cables,” Whitley said. “That avoids the expense and the alignment difficulties of drive shafts, and greatly reduces lost space in the cargo bay. It lets us put the mud and dry-material tanks exactly where we want them for best stability and trim.”
Another advantage of the house-forward design is the efficiency it provides in the exhaust system. “We’re able to route the exhaust stacks straight up from the engines,” Whitley explained. “That avoids the loss of efficiency caused by deflecting the exhaust stream outboard to side-stacks.”
The Orleans’ huge cargo bay is able to carry 7,133 cu. ft. of bulk material and 5,107 bbls. of liquid mud. The liquid-mud tanks are designed so there’s no internal structure. With completely smooth interiors and fixed Butterworth washdown systems, they rarely have to be opened for cleaning. The vessel’s two Mission Magnum 5" ´4" ´14" pumps deliver mud to a height of 196' above the water, and her two 80-psi air compressors deliver 50 metric tons of dry cement or barite per hour to the same height.
The vessel’s hexagonal wheelhouse contains a head and refreshment station in addition to the forward and aft steering consoles. At the forward console, the operator faces two completely redundant Alstom ADP 21 control panels and plasma-screen displays. To maintain a desired track or position, the system accepts data input from the vessel’s two Furuno ARPA radars, two Leica DGPS receivers, and two Meridian gyrocompasses. In DP mode, a Cyscan laser reference unit provides distance and bearing to the platform. The system even accepts and incorporates wind data from digital anemometers.
MORE TO COME
The Orleans was delivered in early May amid a swirl of controversy regarding her financing.
According to Rigdon, the vessel was issued a U.S. Coast Guard Certificate of Documentation (COD) on May 13. On May 19, the Offshore Marine Service Association and several U.S. Gulf service vessel operators sent a letter to the Coast Guard alleging that the financing for the 10 Orleans-class boats Rigdon ordered from Bender violated foreign-ownership requirements for U.S. documentation.
“The Coast Guard did come to us with some questions,” Rigdon said. “We resolved the issue by obtaining financing for the boats through a U.S. subsidiary of the original financier, France’s Groupe Bourbon. The Coast Guard was satisfied with that and the vessel’s COD has remained valid since issuance. In fact, she’s already out on hire. The matter is closed.”
The second and third boats in the Orleans class will be the Bourbon and the Royal, both already in the water at Bender Shipyard, with the fourth through seventh under construction in the yard.
The Bourbon will be delivered in July and the Royal will follow in September.
“We’re funding the steel for number eight tomorrow,” Rigdon said. “We’ve got the funding for 10 boats. After that, we’ll see what happens.”
He added with a laugh, “Right now, we’re concentrating on putting the first 10 to work.”
Rigdon is confident that the U.S. Gulf will offer steady employment for his new vessels, even at a time when other OSV companies have boats stacked and looking for work.
“It’s a competitive market, and we’re confident these boats can compete in it. Maybe some others won’t, but that’s the free market.”
SIDEBAR
PSV rescue boats need special handling
When Rigdon Marine chose to fit each of its new PSVs with a 14'8"¥6'2" Schat-Harding rescue boat, some adjustments needed to be made.
Norway-based Schat-Harding’s SPMOB 350/3.65/12E davit had to be morphed into a lower profile configuration to fit the design of the Rigdon boats.
“Standard headroom for our davits is about 14 feet,” said Clifford Monaghan, Schat-Harding’s sales representative based in Covington, La., “but on this boat we had eight feet, three inches. This one had to be tucked in. By offering both luffing and slewing davits as well as low-profile configurations, we can accommodate most any deck arrangement we come across.”
The USCG/SOLAS-certified rescue boats are made of fiberglass and were built at the Norwegian company’s New Iberia, La., facility. The boat has a capacity of six.
“The boat is low maintenance, low cost, and will fit in a variety of rescue-boat davits,” said Monaghan. “By building the boat in Louisiana, we save thousands of dollars in freight alone. We can now produce and deliver a boat in less time than it took to ship one from Europe.”
The boats can be launched quickly. From the time the crew enters the rescue boat until the boat is in the water takes about one minute, said Monaghan.
“The fixed davit arm is slewing [swings out] less than 180 degrees, we’re lowering at IMO specific speeds of about 120' per minute, and we’re not going very far. The whole operation meets USCG and SOLAS requirements.”
The rescue boats are powered by 40-hp Johnson outboards that push the boats through the water at 14 knots. The engines comply with the latest USCG and EPA emissions regulations.
Schat-Harding specializes in total lifesaving system packages ranging from design consultancy through supply, fitting, maintenance, and lifetime service. One of its main target areas is the offshore oil and gas industry. — Ken Hocke
RIGDON PSVs SPECIFICATIONS
Builder: Bender Shipbuilding & Repair
Designer: Guido Perla & Associates Inc.
Owner: Rigdon Marine Inc.
Mission: Oilfield service
Length: 210' Beam: 54' Depth: 19'
Maximum Draft: 16'
Main Propulsion: (2) Alconza electric AC motor, 2,100 hp
Z-Drive: (2) Steerprop SP 20
Bowthruster: (2) Berg, 1,000 hp
Propellers: (2) 92" dia.
Ship’s Service Power: (2) Cummins QSK60 diesel engine, 1,825kw; Cummins KTA38, 910kw; Cummins 6CTA8.3 diesel engine, 170kw
Speed: 13 knots loaded; 15 knots light
Hull construction: Steel
Crew Capacity: 22
Tankage: Fuel, 4,881 gals.; liquid mud, 5,107 bbls.; potable water, 5,642 bbls.; drill water, 2,886 bbls.; bulk mud/cement, 7,133 cu. ft.
Electronics: (2) Furuno 2115 radar with ARPA; (2) Leica MX420 DGPS receiver; (2) Furuno FA100A1S auto-identification transceiver; Furuno FE700 depthsounder; Furuno DS80 doppler speedometer; Furuno MX500 Navtex receiver; Furuno FAX207 weatherfax receiver; (2) Furuno FM8500 VHF transceiver; Furuno F1815 GMDSS station; (2) Meridian gyrocompass
Classification: ABS +A1 Offshore Support Vessel +AMS +DPS-2, SOLAS, USCG Subchapter L, Full Ocean
Delivery Dates: Orleans, May; Bourbon, July; Royal, September
