Don’t Be Under Alarmed: Part 2

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In the January issue of The Newsletter, I discussed alarm systems that typically reside on the engine: low oil pressure, high coolant temperature, and exhaust temperature. In this article, I’ll cover other vessel alarms and notification systems that are capable of alerting the skipper to important onboard events.


There are two at-sea disasters that rightfully strike fear into the heart of every cruiser: fire and flooding. No one needs to be told that these emergencies must be taken seriously. What’s worth reminding folks of, however, is the importance of early detection. Because fire can spread very rapidly and because smoke alone—even from a seemingly insignificant fire—can be deadly, it’s vital to do whatever is necessary to ensure that a fire aboard is discovered early. Suffice it to say that you never can detect a fire too soon. (If you'’d like to learn more about onboard smoke detectors, click the following link to read my article from the September ’09, Vol. 2, issue of Channels:

Related to the topic of fire is gas: LPG (liquefied petroleum gas), CNG (compressed natural gas), and gasoline. If your vessel utilizes any of these fuels, it’s important to monitor for the presence or accumulation of potentially explosive vapors. Systems that monitor explosive fumes are readily available, and they are relatively inexpensive. They should be wired in such a way as to ensure continuous monitoring (we’ll talk more about 24-hour power supplies below). After all, a leaking LP gas line or gasoline fuel filter neither knows nor cares whether you are on board. If such a leak exists, you need to know as soon as possible—as soon as you set foot aboard, if the leak occurred while the vessel was unattended, and before you energize any electrical equipment.

Flooding, of course, carries its own set of concerns, and it, too, is best detected as early as possible. For this reason, high-water alarms are an essential component aboard any vessel that’s equipped with a bilge pump. This alarm should be energized by what’s referred to in the industry as a “24-hour bus,” which simply means it’s always on, regardless of the position of the battery switches or whether power is available to the remainder of the house loads, engines, and other equipment. In fact, this is the same power-supply condition that should exist for the bilge pumps themselves: you should be able to leave the boat with all primary DC circuits de-energized, secure in the knowledge that the bilge pumps and high-water alarm will operate.

Automatic bilge pump and alarm power supplies should never be controlled by an ordinary circuit breaker installed on the vessel’s main circuit breaker panel. One approach calls for the use of a separate bus whose supply utilizes a circuit breaker that is protected from inadvertently being turned off. (A fuse may also be used for this supply; however, a circuit breaker is preferred.) Some proprietary high-water alarms utilize an internal 9-volt transistor battery (in some cases, two are used). With this arrangement, there’s no concern that the high-water alarm will fail to sound if the vessel’s batteries are dead.

The high-water alarm annunciator must, by necessity, be impossible to ignore, and it should be audible both in the cabin and on deck. The alarm should be impossible to mute or silence inadvertently. Having an on-deck annunciator ensures that even if you are not on board, people nearby will be alerted to your boat’s distress situation. This “outside” signal approach can be taken one step further with the addition of a wireless alerting system that can be programmed to send you a text message if the high-water alarm (or another alarm) sounds.

I’'m frequently surprised by the high level at which high-water alarm float switches are installed. I routinely encounter switches that have been installed 8, 12, or more inches above the primary bilge pump float switch. Depending on the size of the vessel and its bilges, the difference in elevation between these two switches can represent a great deal of floodwater. The alarm float switch should be installed only slightly above the standard bilge pump float switch—just high enough to prevent nuisance signals. Installing it any higher simply means that much more floodwater will accumulate before the alarm sounds.

Another type of water alarm worthy of mentioning involves the vessel’s fuel system. Water-in-fuel sensors, sometimes referred to as WIFs, and their associated alarms are a necessity for cruising vessels. During a recent conversation with a client, he relayed to me how his brand-new engines had suffered several thousand dollars’ worth of damage as a result of water contamination. During installation of a teak deck, his boat’s fuel-fill caps had not been properly secured, allowing rainwater (approximately 50 gallons!) to enter the tanks. During the next sea trial, water overwhelmed the primary and secondary fuel filters, ultimately reaching the high-pressure fuel injection system. The ensuing damage necessitated replacement of all fuel injectors on both engines. Had the vessel’s primary fuel filters been equipped with water-in-fuel sensors, it’s safe to say that the engines would have been shut down before suffering damage.

Sensors should be installed in all primary filters, including tandem designs, as well as generators. It’s important that WIF sensor alarms be located at both lower and upper helm stations, and they must be loud enough that you can hear them over strong winds and entertainment system noise. Some annunciators simply use an indicator light, which is not prudent, since it may be easily overlooked.


Because the role played by virtually every vessel’s battery bank is critical, it’s important to maintain a close watch on its voltage. A simple voltmeter or amp-hour meter will alert the user to a condition that requires attention. But what happens if a low-voltage condition occurs in the middle of the night? While many battery bank monitoring systems can be programmed to sound an alarm if a low-voltage threshold is reached, most that I’ve encountered haven’t been programmed, leaving a valuable feature untapped.

By the same token, what happens if your boat’s shorepower supply is interrupted? Depending on your boat, this may be a nonevent, or it may be catastrophic. If refrigeration equipment is running, regardless of whether it’s AC or DC, it will stop functioning. If the equipment is DC, the batteries will carry the system for some time. However, they will eventually become depleted, at which point the refrigerator and freezer, as well as the bilge pumps and high-water alarms, will stop working. Once again, if you are aboard, you can clearly deal with this issue, but if the vessel is unattended, there’s little hope for intervention unless an alarm that can be clearly heard outside the boat has been installed.

Battery-operated AC power-loss alarms are available and are worthy of consideration if you are concerned about power loss aboard your vessel while you are away or asleep. This is especially important for refrigerators and freezers that are used to store meat. If meat defrosts, bacteria can grow, causing those who eat it to become ill. If the meat has refrozen, you may never know of the problem. I was carrying out an inspection aboard a vessel recently and found in the freezer a small plastic cup that had been filled halfway with water and frozen. Resting atop the ice was a penny. The owner explained that this was his low-tech (but effective) refrigeration-failure alert system. If the penny ever found its way to the bottom of the cup, it would be clear that the freezer had thawed, which would almost certainly indicate that the food stored within had spoiled.

I recently found myself on the bridge of a 60-foot trawler during a sea trial at which the owner was not present. An alarm sounded, but it was unclear to all aboard just what the alarm was for. There were multiple alarms on board for monitoring such things as engine and generator overheating, exhaust temperature, stabilizer hydraulic fluid temperature, low voltage, and so forth. The situation served as a good reminder that a boat’s alarm system needs to be well organized. When an alarm sounds, it should be immediately clear what it’s telling the crew, and this message should be obvious to anyone who’s operating the vessel.

Alarm basics and proper monitoring of your boat’s systems must not be overlooked. The good news is, monitoring the most important systems aboard is neither difficult nor expensive.