PLC-Based Control Systems Go Off-Shore

Hurricanes Katrina and Rita in 2005 devastated the lives of people in the Gulf States and affected oil and gas production for the entire country. U.S. Interior Secretary Gail Norton reported, “Of the 4,000 platforms that the MMS (Minerals Management Service) administers, 3,050 platforms were in the path of Hurricanes Katrina and Rita.


Hurricanes Katrina and Rita in 2005 devastated the lives of people in the Gulf States and affected oil and gas production for the entire country. U.S. Interior Secretary Gail Norton reported, “Of the 4,000 platforms that the MMS (Minerals Management Service) administers, 3,050 platforms were in the path of Hurricanes Katrina and Rita.” The vulnerability of offshore oil and gas production became frighteningly obvious. Yet, even under normal conditions, the demand for reliable supplies of oil and gas provides logistical challenges. Offshore drilling rigs require a constant flow of people, equipment, water, food, and other supplies to function properly and maintain output.

Offshore supply vessels (OSV), platform supply vessels (PSV) and anchor handling towing supply (AHTS) vessels fulfill supply tasks as they move personnel to and from installations, ship provisions for dozens of platform residents, and maintain a steady supply of critical drilling supplies. These ships, like any land-based facilities, depend on industrial networking and control systems using fieldbus-connected instrumentation, PLCs and Ethernet communication. They are, in effect, mobile industrial installations requiring the same equipment and control functionality.

Their regular runs provide everything from water and food, to oil and lubricants. Any interruption in supply ship services can affect daily oil or gas production with its enormous accompanying expenses, and threaten the comfort if not lives of rig residents, some several hundred miles offshore. Supply vessels constitute the central connection to civilization and must function successfully in a wide range of weather conditions and circumstances.

Bender Shipbuilding's facilities

One of the key suppliers of OSVs and other vessels for the oil and gas industry is Bender Shipbuilding in Mobile, AL. For more than 75 years, Bender Shipbuilding has been a leading manufacturing and repair facility on the central Gulf of Mexico coast. With over 7,000 feet of deep water frontage and multiple yards, Bender's dry docks have the lifting capacity to raise more than 24,000 tons. In addition to OSVs, Bender Shipbuilding builds many vessels, including crabbers, shrimp boats, push boats, and tug boats, as well as passenger vessels. More than 800 Bender-built ships currently operate worldwide.

Although builders of OSVs work at creating distinctiveness and advantages for their proprietary designs, for most OSV owners and operators the central issues remain safety, operating efficiencies, and price. Bender Shipbuilding thus needs an integrated, cost-effective shipboard management system to answer the challenge of making today's OSVs as efficient and productive as possible. In practical terms, the company needs a system that can reduce vessel operating and development costs, increase efficiency, and provide considerable savings in installation and sea-trial time. The management system should also help them stay on schedule and under budget, and provide a high level of operating performance for customers.

Bender Shipbuilding partnered with Prism Systems, a systems integration and engineering firm also based in Mobile. Prism provides shipboard controls and propulsion management systems for the international commercial marine industry. With engineering experience in drives, controls, and operator interface design, Prism Systems successfully designed a modular, PLC-based system architecture to answer Bender Shipbuilding's present and future requirements.

“Bender asked us to create a customized system that would be adaptable, cost-effective, and could easily be upgraded, and we had the platform to do just that,” says Chris Grimmell, Prism Systems' lead engineer on the project. By configuring Prism Systems' Vessel Management System (VMS) to be adaptable to specific vessel requirements, they succeeded in addressing not only Bender's demands for a cost-effective and efficient vessel operating system, but providing system adaptability that ensures the ability to outfit and update future vessels quickly and cost-effectively.

Network support

The VMS package comes standard with support for most common control-network technologies, and Prism Systems' software development team can provide support for almost any type of serial and/or network-based device. As a result, the company easily integrated the vessels' legacy devices and technology into the control architecture. As old and new technology interfaced effectively, it allowed users to adapt to the VMS's more sophisticated control devices. “Most customers want to keep as much of their legacy infrastructure as possible, so our main goal is to provide a system that interfaces easily,” explains Keith Jones, president of Prism Systems.

The VMS package manages all key elements of vessel operation. Its functionality spans a variety of areas including machinery alarm and power management, as well as tank-level monitoring and control of valves and pumps. It uses a redundant Siemens PLC design to make the system more reliable and fault-tolerant. Its visually-rich operator interface allows ease of handling and reduces training time for operators. Ethernet communications among PLCs and servers are redundant to ensure that an exchange of critical information occurs in a timely fashion. Also, all PLC and operator-interface hardware is powered by an uninterruptible power supply (UPS) to add fault-tolerance.

VMS operator-interface systems are deployed in multiple locations, such as the pilothouse, engine room, and captain's and engineer's staterooms. With readily accessible information on the current status of vessel equipment, crew members can watch over systems throughout the ship. Operators can easily monitor and control various valves and pumps for cargo handling and quickly respond to alarms from multiple locations. Beyond helping the crew avoid hazardous situations, such immediate response prevents unnecessary wear and tear, adding efficiency and safety for equipment and personnel.

Durability and adaptability with low maintenance costs are central issues for OSV owners. The VMS had to offer potential for upgrades while interfacing with legacy equipment and functions. This is particularly important for large ships. Prism Systems chose a redundant, distributed Profibus I/O architecture which could accommodate additional functionality in an existing installation and allow engineers to expand the system easily.

Prism Systems' engineering manager Ron Knight explains the advantages of such architecture: “A VMS installation reduces the amount of cabling that must be pulled back to a central location, which makes it less vulnerable, less expensive to install, and allows easier access for alterations and repairs.” Because the VMS collects and controls I/O data over redundant, industry-standard control networks (primarily Profibus and AS-i), it integrates more easily with existing systems and allows easier training and adaptation for the vessel's control personnel. In fact, the VMS supports a variety of additional connectivity to provide seamless communication to manufacturer-supplied monitoring equipment, such as Modbus, RS-232, RS-485, etc.

For Bender Shipbuilding's OSVs, Prism Systems' VMS package includes alarm, data collection, and integrated control systems, all accessible via central operation station consoles. The machinery alarm functions monitor multiple systems, such as the diesel generators, propulsion drive units, bow thrusters, and bilge and tank levels; displaying alarms at various VMS workstations throughout the vessel. Any alarm is immediately sent via Profibus to the alarm-system and power-management processors, thus allowing fast and easy response by operators.

The integrated control system oversees power management functions and dynamic positioning interfacing. The data collection system, which co-resides with the alarm system, monitors tank levels for vessel stability analysis. The VMS continuously monitors these critical areas, allowing personnel to respond more quickly to dynamic and potentially dangerous situations on board ship.

“When they are sitting next to the oil rig and any significant wind gust or wave action could propel the ship into the platform,” Grimmell notes, “the crew needs to be able to monitor all systems centrally, and they need a system that responds quickly to any problems.” The Prism interface monitors the new and prior systems.

Bender Shipbuilding's new VMS reduced vessel operating costs, improved efficiency, adding adaptability and user-friendliness to produce and maintain offshore vessels. This allows vessel operators to train and retrain easily as the vessel's systems remain current with simple upgrades. ce

Author Information

Michael Darnell is vice president, sales & marketing, for Prism Systems Inc., Mobile, AL;

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