SPECIAL REPORT: INNOVATIONS IN INTEGRATED NAVIGATION SYSTEMS FOR VESSEL BRIDGE OPERATIONS
Control and Stability Francis Slade, Staff Writer
When PSVs and OSVs are ‘at work’ they are on their own, so managing their navigation and positioning becomes a very important matter
The use of Multi-Function Workstations connected to the ISMS network with all data available, gives the operator a great deal of flexibility and simplicity in handling and monitoring onboard systems and processes
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N THEIR paper ‘Trends in Ship Management Systems’13 Kos, Hess and Hess at the University of Rijeka explained, “Because of [the] ever expanding complexity of ship structure and machinery, also new safety regulations and class requirements, onboard decision making process becomes more delicate and complex. Consequently, ship management systems should become more extensive and flexible… there is [also] a significant demand for reduction in existing numbers of crew members. Modern marine technologies and improved ship management systems should solve these problems [without] compromising safety of the ship.” The challenge of ever more sophisticated and extensive engineering capabilities is the need to control them and their growing complexity. Kos, Hess and Hess concluded that the complexity could actually compromise safety and operability but that integrated ship management systems hold out the promise of solving that problem. They went on to state, “The use of Multi-Function Workstations connected to the ISMS network with all data available, gives the operator a great deal of flexibility and simplicity in handling and monitoring onboard systems and processes.” Perhaps the most important role of ship management for OSVs, PSVs and other vessels likely to come near to an offshore platform, is stability and that isn’t so easy to achieve on an ocean, even in calm conditions, leave alone less than calm. But, whereas once, a ship’s master really had only the propulsion and rudder to direct a vessel, these days ships employ a number of systems to support good conning and aid stability. Conning, the determination of speed and direction, may accept some leeway when out at sea but when maneuvering near an offshore platform, there is no leeway if a potentially disastrous collision is to be avoided. Two principal systems support the conning officer; thrusters and dynamic positioning.
Directional Control Has Evolved Into a System As we briefly mentioned above, there was a time 10 | WWW.OFFSHORETECHNOLOGYREPORTS.COM
when the only means to control a ship’s direction were propulsion and rudder. A screw propeller is a simple thruster operating on a fixed shaft pushing the ship forward and needing a rudder to steer. However, a rudder can only determine the direction of forward movement. Using thrusters that can deliver propulsion from different or even varying angles allows a ship to maneuver in confined spaces or places where movement in constrained by proximity of a structure (offshore platform). Some thrusters use traditional looking propellers while others use water jets to apply directional pressure. Also, some are fixed in their direction while Azimuth thrusters are positioned in maneuverable pods so that their direction of steering pressure can be rotated in any horizontal direction. Bow and stern thrusters are, as the name suggests, placed at the bow or stern of a vessel, to improve maneuverability. Bow thrusters help with docking because they allow the vessel to be turned to port or starboard without forward motion. A stern thruster does a similar job at the stern. But any such system with, often, multiple propulsion deliveries, has to be controlled if it is to be effective.
Dynamic Positioning Makes Control More Accurate Offshore support vessels use thrusters to achieve and maintain position relative to an offshore structure using their Dynamic Positioning (DP) systems along with the skills of the ship’s officer. In its feature, ‘Dynamic Positioning an amenity becomes compulsory’14, MarineLink.com explains that, “The inclusion of dynamic positioning systems has become a standard and necessary system on supply boats and many crew/supply vessels. In their simplest form, dynamic positioning systems allow an offshore vessel to ‘moor’ adjacent to a rig or platform without the traditional mooring lines being attached to the structure or the use of anchors. Instead thrusters both in the bow and the stern keep the vessel on station.” Technologically, dynamic positioning systems are hydrodynamic systems that manage the position and heading of a vessel. They can either be