Much of the time I'm the only adult aboard my boat. I either single-hand or cruise with my young daughters. And one particular risk troubles me more than all the others combined: What if I fall overboard?

Alarms can alert parents if children go over – and some can stop the boat if it is a parent who winds up wet. There are several products designed to raise the alarm and assist with the recovery of crew overboard. To be clear, these systems are distinct from distress radio beacons such as EPIRBs and Personal Locater Beacons (PLBs), which help search-and-rescue authorities locate boats and people in distress.

Instead, man-overboard (MOB) alarms alert the boat's crew that one of their crewmates has fallen off the vessel. It works like this: A transmitter is attached to each crewmember – usually a small tag, about the size of a car remote – and a receiver is installed aboard the vessel. The receiver sounds an alarm automatically when a crewmember falls overboard. Most transmitters have a button or switch that allows crew members to manually activate the alarm as well.

Most receivers can also trigger the MOB function on a GPS or chart plotter, generating a waypoint using the vessel's position at the splash point. Many can disengage the vessel's engines or activate other MOB-recovery gear. Some systems can even provide real-time direction finding to help recover the crewmate in the water.

Overboard preparation is a priority for all experienced boaters, particularly those who venture further from shore. MOB alarms have gained in popularity in recent years, with roughly a dozen companies – including Raymarine, Mobilarm and Autotether – adding to the arsenal of modern safety gear now available.

Although the best advice remains "Don't fall off the boat," the fact is that falls overboard, along with capsizes, account for the biggest share of boating fatalities reported to the U.S. Coast Guard. Ninety percent of drowning victims are found without personal flotation devices, or PFDs. So wear a lifejacket when onboard. My children even wear them on the dock.

Once a crewmember has fallen into the water – hopefully with a PFD on – the top priority is getting him or her back aboard. The sooner the engines can be stopped, or a GPS waypoint set, the better. Ideally, falling in the water would trigger an audible alarm, set a GPS man-overboard (MOB) waypoint and stop the boat.

The MOB alarm systems currently available use one of two basic operating principles. It is important to understand the distinction between the two to select the right one for you.

PROACTIVE OR REACTIVE

Proactive or proximity systems are activated when a constant signal produced by the transmitter, worn by a crewmember, is interrupted. Signal interruption might occur due to an increase in the range between the transmitter and the receiver, as when a crewmember falls overboard. However, an interruption could also occur if the transmitter were unable to transmit due to radio-frequency interference from other equipment, a discharged battery or damage to the transmitter itself. False alarms are more likely with these systems because any disruption in the signal triggers an alarm.

Reactive systems are activated when the transmitter, worn by the crew, is immersed in water. However, if the transmitter or its battery fails, no alarm is triggered aboard the vessel, so it's possible to experience a situation in which somebody has fallen in the water but no alarm is triggered. Transmitters remain off most of the time, so there is little drain on their batteries. Some reactive systems use a direction-finding antenna aboard the vessel to help the crew locate the MOB.

So which is better?

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.

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.

Before you buy, consider the product features and operating modes within the context of your own vessel, your typical crew and your cruising style. Having said that, there are some basic items to consider when conducting your own assessment.Some alarms interact with a chart plotter to set a waypoint at the location of the splash.

If you've got a steel or aluminum hull, you'll probably want to stick with a reactive system, since proactive systems can produce false alarms when the radio signal is disrupted.

If you cruise primarily protected inland or coastal waters, real-time MOB tracking may not be necessary. A simple MOB waypoint will provide all the location data you'll need to get the vessel back to the person in the water. Even with a strong tidal or river current, the victim's location will not likely be a mystery, since they will probably be downstream of the splash point.

If you cruise offshore, where you're likely to encounter heavy weather, direction-finding gear may be more important, although some will regard the fail-safe nature of proactive "alarm-on-failure" systems more compelling. Unfortunately, there are currently no systems that combine the utter reliability of proactive systems with the direction-finding capability of reactive systems.

If you cruise shorthanded in a powerboat, your top priority in a MOB situation may be stopping the boat; an alarm that can be rigged to kill the engine might suit you best. If you venture into wilderness areas, afloat or ashore, you may want to select individual PLBs for the crew instead of, or in addition to, a MOB alarm. These can help rescuers find you in the event of mishaps of all kinds, not just falling overboard.

If you cruise with children, you'll often have your hands full, especially while leaving or arriving at moorages. You might want to select a system that requires minimal hands-on effort to engage and disengage; chasing down the kids to collect or turn off their sensors could become bothersome.

READ THE MANUAL

No matter your situation, be sure you understand how each system really works in practice. Most of the manufacturers make their installation and operation manuals available online. If not, call or email them and ask them to send you a copy. I urge you to read these manuals all the way through to be sure you understand what's going to happen.

Marketing materials aren't likely to point out the factors you will find most annoying in practice aboard your vessel, but the information is available, if you take the time to find it. All the manufacturers with whom I've corresponded have been extremely helpful and forthcoming about their products' capabilities and limitations.

Once you select a system and install it, practice with it. Throw a floating cushion over the side with a sensor attached and see what happens. Walk away from the boat and see how range affects the system's performance. All the systems include procedures for commissioning and testing. Do that. Adjust the test procedure: throw in some monkey wrenches of your own, relevant to your situation. It's important for you and your crew to be aware of the system, how it works and what they should do if somebody falls overboard.

Researching this article has helped me identify the best solution for my C-Dory, a small, outboard-powered cabin cruiser frequently operated shorthanded, with children aboard. Underway, the top priority is to stop the boat immediately, especially if I'm the one in the water. I can swim several yards to the boat if there's no adult aboard to come back for me. Of secondary importance, I want the kids to keep their transmitter-equipped PFDs on when they're exploring new ports of call, and I don't want to spend my time managing MOB transmitters every time we get underway or disembark.

My circumstances call for a low-effort system designed around engine shut-off, with small, tamper-resistant transmitters the children aren't likely to damage. GPS waypoints and real-time tracking are relatively low priorities for my boat. There are only two products on the market that meet all my criteria: the MariTech Virtual Lifeline and the Autotether.

With the right system aboard and a little practice on your part, you can stack the deck in your favor in the event of a fall overboard. With luck, you can turn a potential tragedy into another great sea story.

Tim Flanagan is managing editor of Navagear.com, a blog that covers equipment for cruisers.