Alert2 (www.Alert2.com) consists of the vessel-mounted AR100 receiver ($500) and any number of AT101D transmitters ($235 each). A third component of the Alert2 system is the APDF100 Portable Direction Finder ($800), a rugged handheld directional antenna and receiver that allows the vessel's crew to locate the MOB transmission by sweeping the horizon.
In operation, the AR100 receiver remains active while underway (or in port, if appropriate). The transmitters remain dormant until triggered, as with all reactive systems, and the APDF100 unit is stowed where it is accessible in an emergency. Once triggered, the AT101D transmits a coded 418-MHz signal to the AR100 unit aboard, which sounds an alarm and can, if wired to do so, shut down the engines or tell the vessel's navigation system to generate a waypoint at the splash point.
Upon hearing the alarm, a crewmember aboard the vessel deploys and activates the APDF100, sweeping the area to determine the bearing to the victim. As the vessel is brought around and rigged for MOB recovery, the spotting crewmember continues verifying the relative bearing with the direction-finding receiver until a visual sighting is made.
Alert2 is a serious tool well-suited to offshore passagemakers and commercial vessel operators. Assembled in the United States from a combination of custom-made and commercially mass-produced components (yes, the transmitter is contained in a waterproof Princeton Tec flashlight housing), Alert2 represents the least expensive direction-finding MOB alarm system on the market.
ACR's (www.acrelectronics.com) MOB alarm system uses the Vecta2 receiver ($1,429) and the Mini B 300 water-activated Class B EPIRB ($330). The Vecta2 cleverly serves as both a vessel-mounted alarm monitor and, when removed from its cradle, a handheld direction-finding receiver. The Mini B 300 should not be confused with a traditional EPIRB, and it's likely that ACR will remove the "EPIRB" designation from this product when Cospas-Sarsat stops monitoring the unit's 121.5-MHz signal.
Despite this change in status, however, 121.5 MHz remains a viable short-range homing frequency, which means that ACR's system is compatible with equipment already onboard many search-and-rescue aircraft and vessels. Operation is similar to the Alert2 system, although the Mini-B 300 transmitter's antenna must be deployed by the victim to achieve full range. All direction-finding systems achieve maximum range when the victim is able to hold the transmitter up out of the water.
The Sea Marshall (www.seamarshall-us.com) system's SARFinder 1003 base unit ($2,795) uses a three-element, vessel-mounted antenna and sophisticated direction-finding radio gear to provide a relative bearing to the MOB right at the helm, with no hand-held horizon sweeping required. Sea Marshall SMR8-LR transmitters are $295 each, and feature an antenna that must be deployed by the victim for maximum effectiveness. Sea Marshall, like ACR, uses the 121.5-Mhz search-and-rescue homing frequency.
The Sea Marshall system is the most expensive of those surveyed here, due to the clever direction-finding receiver and helm display, as well as the complex antenna. Because it requires less effort on the part of the crew remaining onboard, Sea Marshall may be the only MOB-tracking system usable by shorthanded crews. For instance, if only one or two crew remain aboard during a MOB event, they may be unable to operate the ACR or Alert2 handheld receivers while simultaneously maneuvering the vessel, particularly aboard sailboats.
I haven't covered every MOB alarm system here, just those widely available in North America. Several systems are either in development or available elsewhere, but not yet here. These include proactive systems AMEC Amulet, MOB Guardian, and NKE Marine Electronics, as well as reactive systems SeaSafe, Mobalarm, and WaveFinder.
In addition, reactive systems are being developed under at least two names – Deep Blue and Mermaid ID – that use a sonar-like ultrasonic digital pulse to communicate with the vessel, rather than regular radio-frequency transmission. The receiver, in this case, uses a through-hull hydrophone transducer rather than a conventional antenna.
YOUR BEST BET
In short, they're all winners. As Page Read, founder of Emerald Marine Products, puts it, "There's a market for every one of these products." This is the fellow who designed the Alert2, but he doesn't bad-mouth his competition. He's very much aware that the features most important to offshore sailors will differ from those of freshwater anglers, harbor-hopping cruisers with children, or commercial fishermen.
