Bilge Pump Alarm:
Adding Visual and Audible Alarms
to High and Low-Water Pumps

by Rick
July 25, 2009


Water, Water Everywhere

All boats leak. Or so I've heard. And when we took possession of Sea Gator she was no exception. I remember vividly the first few minutes onboard our first night. Her batteries had been run down, the lights were dismally faint and the sound of splashing water was unsettling. With a flashlight I looked in the bilge and, sure enough, there was water. My immediate thought was that Sea Gator was sinking. I soon realized the sounds were from wind waves lapping at the hull. To this day, I still greet the site of water in the bilge with unease.

Leaky Boat With time, I learned the source of much of our bilge water was the steady dripping of the propeller shaft's stuffing box. The rudder shaft's stuffing box and leaking raw water strainers for the heads also contributed to the bilge water. And we've had our share of fresh water leaks to keep our bilge pump busy.

After I repacked the stuffing boxes with new "virtually dripless" stuffing and attended to all other leaks, we had a dry bilge for some time. I knew water would eventually return to the bilge so an alarm was on my project list.

The idea for my bilge alarm originated with Skipper Bob's "Cruising Comfortably on a Budget". In his book, Skipper Bob describes a simple bilge alarm using a helm light and 12 Volt DC (VDC) door chime. While under way the helm light would alert him when his bilge pump activated and the door chime offered an early warning to problems if it rang longer or more frequently than normal.

Design Goals

Following Skipper Bob's lead I decided exactly what I wanted in a bilge alarm. I wanted an audible alarm and warning lights for both our low (or main) and high (or secondary) bilge pumps and I wanted them at both helm stations.

Sea Gator came equipped with a single alarm located near the lower helm, which sounds loudly if our secondary bilge pump, located about six inches higher than the main pump, is activated. While its sound is piercing within the cabin it's possible we would not hear it while piloting from the flybridge. Audible and visual alarms on the flybridge would alert us to any problems while we are under way. Also, if I could hear an alarm for the main pump throughout the cabin, I could use its sound to verify that the duration and frequency of pump activation were normal. Separate warning lights for both bilge pumps would also be important to reveal a real problem.

I created the schematic, above, to document what I had in mind. When the low float switch activates the main bilge pump, yellow LED1 will light and the buzzer will sound. Similarly, if the high float switch activates the secondary bilge pump, red LED2 will light and the buzzer will sound. Diodes D1 and D2 prevent the low-water float switch from lighting LED2 and vice versa. Toggle switch S1 is used to disable the buzzer while investigating the problem. I also thought it would be neighborly to use the switch to disable the flybridge helm's alarm while anchored in a quiet anchorage.

I used a solderless breadboard to test the schematic using momentary pushbutton switches to simulate the float switches. With the diodes oriented properly the LEDs lit and the buzzer sounded. Above, the blue outline shows the components I needed to create my bilge alarms. I would need two units, one for each helm station. Each bilge pump alarm would have three connections. One 12VDC wire will be connected to the bilge pump side of the low-water float switch and the other will be connected to the bilge pump side of the high-water float switch. The third wire will be connected to ground.

Build It and the Water Will Come

Unassembled Since two LEDs, two resistors, two diodes, one buzzer, and one switch don't require much space I decided to make the alarms small so they would be unobtrusive at each helm station. I found two (actually, one that I cut in half) small plastic pieces in my parts bins that would work nicely. The picture at left shows all components but the buzzer soldered and ready to install in the plastic box.

Components The picture at right shows the two plastic boxes, painted, drilled and ready for component installation. I painted one black and one white to match each helm console. Later I found a perfect position for the flybridge alarm within the Ford Lehman instrument cluster so black for both would have sufficed.

The picture below shows the two completed bilge alarms with externally mounted piezo buzzers. The buzzer on the white alarm is a waterproof version for installation at the exposed flybridge helm.


To install the bilge alarms, I connected each wire of a two-conductor 18AWG marine grade cable to the bilge pump side of the low and high water float switches.

Completed Alarm With ground sources readily available at each helm station, only two conductors are necessary.

I ran the cable to the lower helm station and connected the two wires to the bilge pump alarm and to the cable to the flybridge. I ran the cable from the lower helm to the flybridge and connected the wires to the flybridge alarm. At each helm station, I connected the alarm to a suitable ground.

To test, I simply lifted the float on each bilge pump's float switch to momentarily activate the pump. Flipping the bilge pump switch in our DC electrical panel, which activates the lower bilge pump, also tested the low water side of the alarms.

It Works as Advertised

With the bilge pump alarms installed, we now rest easier knowing the alarms will give us early warning of any new problems. Before we get underway, I flip the toggle switch on the flybridge alarm to activate the buzzer. Once docked or anchored I turn off the flybridge buzzer since we always leave the lower helm's alarm activated.

Installed Alarm at Helm Within weeks of installation the alarms easily saved a bilge pump. We were onboard when the alarm activated on its own for the first time since installation. I waited for it to turn itself off. It did not turn off so I turned the buzzer off and waited for the yellow LED to turn off. It did not turn off.

I checked the bilge pump and found that it was running dry. Lifting the float on the switch increased the speed of the pump but the pump would not stop. The alarm had alerted me to a bad float switch: when water (gradually accumulating via the prop's suffing box) reached the base of the lower float switch and long before floating the float, it infiltrated the switch's housing and conducted enough current to run the bilge pump, albeit at a slower speed. Without the bilge pump alarm we would have surely destroyed a new bilge pump by running it dry. I simply installed a new float switch and we were back in business.

Eventually the alarm's buzzer helped me learn that our lower bilge pump normally activates about once a week.

Shortly thereafter, when it activated twice in about 24 hours, I knew something else was wrong, and upon investigation I found a leak at the connections to our fresh water accumulator. The alarm prevented an unnecessary loss of fresh water.


With Skipper Bob's suggestion and a little bit of work, we now have low and high-water bilge pump alarms that will alert us to pending trouble. I particularly appreciate knowing we have an early warning system while we are underway piloting from the flybridge. Anything that helps keep the water outside the hull is a good idea.

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