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Drive enabled electronic thrusters improve Dynamic Positioning

The Gulf of Mexico waters extending from the coasts of Texas through Florida are home to ten of the fifteen busiest ports in the United States, a world-renowned fishing and shrimping industry, and nearly 4,000 offshore oil drilling platforms. This creates a fertile environment to promote a strong shipbuilding industry, with the 1,600 mile coastline dotted with numerous companies specializing in ships of varying sizes, for varying applications.

Alabama has the largest concentration of builders of metal fabricated vessels under 300 feet in the country. One of those companies, Master Boat Builders Inc. of Bayou La Batre, has established its niche by building highly sophisticated offshore supply vessels to serve the oil industry.

The company started in 1979, initially building fishing boats, before expanding into small offshore supply vessels. Since 2000 they have focused primarily on the supply vessels, each year expanding the build size capability. With an emphasis on technical sophistication, quality and durability, the ships are capable of travelling in open seas anywhere on the globe.

Master Boat cultivated its oil rig supply boat business, in large part, by being one of the first builders to transition to thrusters powered by electric motors and variable speed drives. The electronic thrusters provide numerous benefits over their hydraulic predecessors, and are highly compatible with the Dynamic Positioning (DP) systems that automatically maintain a vessel’s position while it is serving an offshore oil platform.

Baldor motors and ABB drives have been integral components of Master Boat thrusters since the early stages of the transition, because both components are uniquely able to withstand the harsh marine environment and the tremendous demands of the DP system.

Electronic thrusters and the beginning of a long relationship


As Master Boat began to grow they forged a relationship with Gulf Coast Air & Hydraulics Inc., located 25 miles up the road in Mobile. Founded in 1985, Gulf Coast began the marine portion of its business doing engine control and steering work on tug boats.

Thirty years later Gulf Coast is a full line distributor and fabricator specializing in air, hydraulic and electric products and services for the heavy industrial and marine markets. Along the way they have become one of Master Boat’s most valued suppliers.

Gulf Coast’s early work with the offshore boats included supplying mechanically operated bow and stern thruster systems driven with hydraulic motors. The hydraulic systems were loud, relatively complex and inefficient, and a potential environmentally liability if a pipe or hose broke at sea. As alternative technologies began to evolve and become more available, boat owners began to demand a change.

“In the mid-2000s or so, Master Boat told us they were going to build a boat with electric thrusters and variable frequency drives, and asked if we were willing to learn the new technology,” said Chuck Moorehead, Gulf Coast president and co-founder. “Being able to fall into the variable frequency drive technology changed everything for us.”

In addition to the environmental safety benefits, electronic thruster systems are far safer to operate and service than hydraulic systems, creating less risk for crew members and allowing boat owners to carry less insurance. They are also easier to install, cheaper to operate, and more efficient.
The biggest benefit of the electric thrusters, however, is how smoothly they interface and respond to the sophisticated Dynamic Positioning (DP) systems that are required by the American Bureau of Shipping (ABS), and the oil companies that contract the boats to supply their offshore oil rigs.

Dynamic Positioning systems and the orchestra of control


A DP system is an automatic operational mode that triangulates between GPS satellites to maintain a vessel‘s position within a 1 to 3 meter radius. It is typically used while a ship is in very close proximity to an oil rig while loading and offloading materials and supplies. When engaged, the DP System simultaneously and continuously controls the bow thrusters, main propulsion system and rudders to hold the ship in place, no matter the wind, current or wave action. The orchestra of control is essential in the supply process to keep a boat from hitting the floating oil rig, and potentially moving it off its mark, causing major damage while drilling in three to five mile sea depths.

“DP systems became a requirement on almost every offshore supply vessel operating in the Gulf,” said Andre Dubroc, the general manager of Master Boat. “We had to move along with that new regulation and ensure that all of a boat’s equipment could meet the rigors of operating under dynamic positioning.”

From a macro perspective there were immediate DP system benefits realized by moving from hydraulic to electric thrusters. In general, the interface of an electric motor and VFD is more efficient, the system reacts far quicker and requires less maintenance.

The electric system also eliminated the complex interface between the mechanical thrusters and the DP software required with the hydraulic system; including an electronic board that converted signals to a processor that drove the hydraulic motor coupled to the shaft of the thruster. The intricate set of moving parts limited the performance of the DP system and was prone to frequent breakdown.

The motor and drive package – especially suited for intense demands of the DP system


Before bringing Gulf Coast into the electric thruster initiative, Master Boat had contacted a Baldor Electric distributor for initial information about potential electric motor and drive products.

“Gulf Coast was already providing 24/7 service to Master Boat and their customers on existing ships, so bringing them into the electronic thruster equation made sense. Master Boat also saw the benefit in purchasing product and service from one organization, so Gulf Coast became involved in the electric thruster business, setting the stage for further growth,” said Mike Mitchell, the ABB application manager who has worked with Master Boat on the electrical systems from the beginning.

In 2011, just after ABB acquired Baldor, the switch was made to the ABB ACS800 VFD and the Baldor RPM AC motor, providing additional system performance and longevity.

The ABB motor and drive package is especially suited for the rigors of the marine environment and the intense demands of the DP system.

“Because of their modular construction the ABB drive is perfect for the marine industry. When you are under contract to an oil company, the people way out on that rig are depending on the boat to bring groceries, fresh water, cement or whatever their needs might be. You just cannot have any extended downtime,” said Moorehead.
Relative to the DP system the advantage of the ABB package is performance. When the vessel is on station or in a positioning mode, depending on wave height, current and wind, there can be quite a demand put on the thrusters depending on the position of the boat. The ability for the ABB ACS800 and the Baldor RPM AC motor to execute very quick and rapid accelerations and decelerations simplifies the positioning process.

“In the DP application, the VFD will typically be ramping from 1,000 rpm in one direction to 1,000 rpm in the other direction in less than 10 seconds - a full reversal in less than 10 seconds. You can’t do that consistently with a standard induction motor and a standard scaler type VFD, they just can’t take the abuse,” said Mitchell.

The direct torque control (DTC) technology in the ABB drive, and the low inertia aspects of the AC motor, provide excellent control throughout the entire speed range, from 2 rpm to 1,800 rpm. They allow highly efficient acceleration, deceleration, and full reversals, reducing generator load and increasing the overall performance of the system.

Master Boat’s Dubroc added, “These boats will basically hold in 10 Knots of wind at the beam. In other words, you could have the wind coming from the beam into the side of the vessel and it will hold. If the wind or current was coming from the bow, you could probably hold in hurricane force winds.”
Bow and stern thrusters are also used for docking the boats and maneuvering in tight spaces like rivers and canals where boats may be passing within three feet of each other. The demand on the drives is not as severe as in the DP system, but precise performance is still required. The thrusters essentially allow the boat to move sideways to negotiate tight spaces without the need for a tug or push boat.

A custom drive cabinet for a tight fit


Master Boat's new class of 220 foot vessels contain the fourth iteration of drive enabled design at 800 hp. This move increased the width of the drives beyond the tight space allotments of the boat, where every inch of space is a premium. Working together Master Boat, Gulf Coast and ABB created a custom design that reduced 30 inches of width on each drive cabinet, saving five feet of space with the two cabinets mounted side by side.

“By everybody collaborating together ABB basically created a whole new drive for us,” said Moorehead.

ABB provides a complete system including the drive and the motor, and then works with Gulf Coast to integrate them into the master DP control system, from initial engineering through to commissioning and start-up.

Gulf Coast supports the effort with an experienced staff that has all the Homeland Security clearances and insurance necessary to fly out to an oil rig or directly to one of the larger offshore supply vessels, covering the area from Brownsville, Texas to Tampa, Florida.

“In ten years I think we have had three warranty calls. That’s not a bad record when you are operating electric motors in some of the worst conditions possible,” said Moorehead.

Additional motor/drive applications on offshore supply vessels

As the Master Boat building team and their boat owner customers have become more comfortable with the electronic systems, motor and drive packages have spread to other areas of the offshore supply vessels. Since 2012 the electronic packages have been used in the following areas:

  • Mud Pumps: an efficient mud delivery system that increased efficiency and eliminated some existing mechanical issues. It allows softer starts so the mud pump doesn’t go right to 1,800 rpm, potentially damaging the hoses and pipes. Mud, or liquid cement, is used in the oil drilling process.
  • Ventilation Systems:  allows better control of the fans that ventilate the engine room, efficiently varying the loads to better balance air inflow and outflow.
  • Fire Pumps: allows operators to vary the speed of the water flow to feather the water load to whatever spot is desired, providing better accuracy in fighting fires. It also eliminates the huge back pressures that result when controlling the water flow with the nozzle.
  • Deluge Pumps: to better control the fire protection system on the ship.

Preparing for bigger boats and bigger challenges


At of the close of 2015 there are at least 60 Master Boat built vessels floating around the Gulf of Mexico with Baldor/ABB drive systems powering the thrusters, the vast majority of them integrated by Gulf Coast Air & Hydraulics.
Gulf Coast sees challenges and opportunities ahead, and understands that the boats, along with their electronic motor and drive packages, will need to evolve.

“Our big challenge moving forward is that the boats are going to get bigger and the thrusters are going to get bigger. The drives will need to get bigger in power, and we will need to further custom-size them so they fit within the limited space in the boat,” forecasted Moorehead on the prospective future of the marine industry in the Gulf of Mexico.

“Those challenges are where great partnerships excel. ABB came in and did a great job of making everyone feel comfortable about what we were installing, how it would interface, and how it would operate on our first sea trials,” said Moorehead.

“And the support from ABB has been outstanding. If a customer has an issue that I can't answer, there is always someone available at ABB that can take that call, run with it, and help. There's not been one time that we needed a body that within 24 hours they were able to respond. And that's what keeps us ahead of our competition.”
 

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Master Boat Builders, based in Bayou La Batre, Alabama, specializes in offshore supply, fishing, and dive support vessels for quality minded customers.

Electronic thrusters offer many benefits over their hydraulic counterparts.

Dynamic Positioning (DP) systems have become a requirement for the boats supplying offshore oil rigs.

ABB’s industrial drives interface smoothly with the Dynamic Positioning systems.

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