by Larry Pearson
Shipboard monitoring, sensing and control systems
are in a transitional phase in 2002. Many of the newest vessels being launched today are using traditional monitoring systems with large alarm panels using banks of warning lights hard wired to 64 or more critical points on the vessel.
These systems give warning if the system being monitoring falls or rises outside of the set point. "The problem is this method of monitoring doesn't give us the parameters the operator needs to diagnose the problem," said Jack Rowley
, general manager of Engine Monitor, Inc., (EMI) St. Rose, La., a leading manufacturer of electronic ship monitoring equipment.
For example, if a high oil temperature is indicated on the port side gear, all the operator knows is that it has risen above the set point, but no other information is given "Today the need is for more and more real time information and the industry has been moving steadily to totally integrated systems on workboats with computer screen readouts replacing warning lights," Rowley added.
"We aren't there yet," Rowley explained, "but many of the larger vessels are installing parts of what someday will be a totally integrated system that pulls together the dynamic positioning navigation system, critical system monitoring, tank levels, control of bulk and liquid mud delivery systems, engine monitoring and all other systems on a vessel that needs to be either monitored or controlled.
The ideal system is based on redundancy and integration as shown in Figure 1 (Above). A dual ring Ethernet system is used as the backbone to insure no failure of the critical bus topology. "Hot Backup" PLC's (Program Logic Controllers) provide the redundancy and interconnection of the external sensors and distribute them to the bus and then to the monitors which can be located throughout the entire vessel.
Any monitor attached to the Bus can have access to any information available on the Bus. Loss of a single PLC in the "Hot Backup" mode will not result in any loss of information or data and will be transparent to the user with the exception of the loss of PLC alarm.
The dual Ethernet ring programmable logic controllers handle all alarm monitoring, tank levels, mud control, engine order telegraph, and is expandable to additionally add navigation information and even add customer required information.
The key to the successful use of computer-based systems is to insure the ABS mandated redundancy at all levels to be sure that no single point failure exists.
Figure 2 illustrates a typical computer screen for port and starboard main engines. Simply analog gauges show real time values such as oil pressure, engine RPM, oil temperature, water temperature and exhaust stack temperature for each engine. Gear oil pressure and temperature are also shown in an analog matter.
The gauge also indicates high and low preset values as well as a digital readout of the real time value. If any gauge indicates an alarm condition, the face of the dial changes from blue to orange. Warning lights control four monitoring points only and all temperature values can be read in Fahrenheit or Celsius at the touch of a button. Variations of these types of screens exist among vendors with some showing mimics as well as the gauges.
The generator page (Figure3) indicates the real time values of each engine powering a generator and an LCD-type read out of generator values. Note that the starboard generator is showing an out of range exhaust stack temperature and that analog readout has changed color from blue to orange to demand immediate attention.
In addition to alarm monitoring, tank and bilge levels can also be monitored as shown in Figure 4. This screen shows in either percent or actual values (gallons or liters) the condition of the six fuel oil tanks, two day tanks and the emergency generator tank superimposed over the plan view of the hull that indicates the relative position of each tank. Another screen shows the same plan view of the hull with the condition of each ballast tank, potable oil tanks, gray and black water tanks and any other tank in the hull such as liquid mud, bulk mud, rig water or methanol. If the hull has a walk-in cooler and/or a freezer, those temperatures can be displayed as well.
While these computer screen displays give real time information, it is also helpful to look at how these values may change over a preset time. Figure 5 shows variations in oil temperature over a five-minute time span of the starboard and port main engine.
The reason why these touch screen-monitoring systems are just beginning to be installed on the largest platform supply vessels is obviously cost. But this too is changing. The cost of computers, the software to run them and the expense of program logic controllers is coming down. There are other savings as well driving down the installed cost of such systems.
"Wiring costs for these computer systems is significantly less than for hard wired sensor systems," Rowley said. Savings in crew or at least using the same number of crew more efficiently also looms on the horizon using these computer-based systems.
Some vessels can now qualify for periodically unmanned engine rooms. "The more controls, sensors and alarms put in an engine room lessens the need to have it occupied," Rowley added.
Another force behind computerized monitoring is the growing popularity of dynamic positioning systems. "DP systems introduce computerized touch screen control to the pilot house so its natural to add a few more computer screens to upgrade monitoring, sensing and control systems," Rowley said. Another unique development is the ability of major engine manufacturers to send data directly to the monitoring system using a serial bus. Caterpillar's Customer Communications Module (CCM) supplies an extensive amount of engine data directly to the ship's monitoring system without adding additional engine sensors. Cost savings in sensors and the cabling to connect them is saved providing another offset to the increased cost of computer based systems.