The biggest benefit of proactive systems is reliability. It's essentially impossible for a transmitter-equipped crewmember to leave the vessel without triggering an alarm. The major drawback is that false alarms are likely, perhaps even probable, since any interruption in the transmission triggers an alarm. A secondary drawback of the proactive system is that the system can't be used easily at anchor or in port, because every crewmember who leaves the boat for any reason will sound an alarm.
For this reason, proactive systems require active transmitter management; crewmembers have to leave their transmitters aboard – or the system has to be disabled – every time somebody leaves the boat intentionally. Proactive systems cannot be relied on to alert you that your guests have capsized the dinghy or your child has fallen off the dock.
One advantage of some reactive systems is real-time tracking. Receivers with direction-finding antennas can provide a bearing to the MOB's current position, not just a waypoint indicating the vessel's position when the alarm first sounded. Another advantage is that, because the system remains passive until triggered, crewmembers can keep the transmitters attached to their PFDs all the time. Nobody has to remember to take it off before going ashore or put it back on later. This improves the chances that the transmitter will be there when needed, even in port or at an anchorage.
For vessels with children aboard, a reactive system eliminates the need to juggle transmitters in port; the kids can continue to wear their transmitter-equipped PFDs, and you can keep the system active or not, as you judge appropriate. The biggest weakness of a reactive system is that transmitter or battery failure triggers no signal, and therefore no alarm.
PROACTIVE SYSTEMS
Raymarine's LifeTag (www.Raymarine.com) integrates easily with Raymarine multi-function displays using the SeaTalk data and power interface. Installation is easy, and the system can track up to 16 separate sensor/transmitter units, called "pendants." Pendant batteries last about a year for typical boaters, since they power off automatically when the base unit is deactivated. They can operate continuously for about 12 weeks, long enough, even, for active bluewater cruisers. The pendant case must be opened to change the battery, so care must be taken not to damage the waterproof gasket.
To minimize false alarms, the system includes a 10-second delay between pendant signal loss and alarm activation. This gives the system a chance to restore contact in cases where the signal was momentarily interrupted for some reason other than a fall overboard. The system can be activated manually by pressing and holding the button on the pendant for three seconds. LifeTag includes an auxiliary 12-volt circuit that could be wired to kill an engine or deploy some sort of automated recovery gear. The list price for a basic system with two pendants is $685.
MOBILARMMobilarm's 720i with six pendants, which crew wear. The MOBi-lert 720i (www.Mobilarm.com) interfaces with other NMEA 0183-compatible navigation equipment, and the rechargeable pendants use induction charging, eliminating the need to open the transmitter case at all. Functionally, it is similar to Raymarine's LifeTag, but may be easier to install aboard boats with chartplotters from other manufacturers. MOBi-lert activates instantly upon signal loss; there is no 10-second delay, as with LifeTag. The base unit also includes an auxiliary 12-volt circuit for triggering engine cutoff or external equipment, but this circuit is subject to a 10-second delay. The system can monitor up to six pendants. The list price for a basic system with two transmitters and charging cradle is $895.
Autotether (www.Autotether.com) is the only proactive MOB system built around engine cutoff, and features the simplest installation of all. It is self-contained and battery-powered, requiring no external wiring at all; not even for an antenna. It's also the least expensive unit available. In use, it replaces the existing engine kill switch clip that fits on a collar around the ignition switch aboard most smaller boats. When the skipper falls in the water, an alarm sounds and the clip pops off the ignition switch, stopping the engine. The skipper's sensor is the only one that kills the engine; the other sensors sound an alarm but do not stop the engine, allowing the skipper to circle around and pick up the MOB immediately. Autotether can track up to four sensors, but the system does not interface with navigational electronics to create waypoints. The base unit is powered by six AAA cells, and the sensors each use three AAA cells, providing about 100 hours of service. The list price for the receiver with two sensors is $295; additional sensors are $69 each.
REACTIVE SYSTEMS.
MariTech Industries' Virtual Lifeline (www.Maritechsafety.com) is described as a "wireless engine shut-off system," so it is similar to the Autotether. Being a reactive system, however, it can accommodate any number of crew sensors. It uses the vessel's 12-volt power system and a separate antenna mounted high and well aft to receive the MOB signal from a sensor.
Although installation is more complex than for the Autotether, operation is simple: It's activated automatically when the vessel's ignition switch is turned on, and it shuts off when the ignition is turned off. Two helm-mounted rocker switches allow control of the system for sensor testing and to engage "rescue mode," which allows the engine to be restarted immediately while the MOB alarm is still activated. Unlike all the other reactive systems, however, real-time tracking is not possible with the Virtual Lifeline. A waypoint can be set at the splash point with some navigational electronics. The list price for the complete system with two transmitters ranges from $539 to $847, depending on engine configuration.
