Remote Boat Monitoring: Bilge, Battery, Shore Power and GPS Alerts on Your Phone

Write down the risks for your boat and where it lives:

• Taking on water (in-water boats): bilge pump activity and high water.
• Battery going flat, which can also stop the bilge pump.
• Shore power dropping out, which shuts off the charger, and in winter, heaters, de-icers or dehumidifiers.
• Theft or break-in: boat movement, doors, hatches, canvas.
• Temperature: freezing in winter, or a hot engine room or fridge.

A trailer boat in a driveway needs location and movement alerts most. A boat in a slip all winter needs bilge, battery and shore-power alerts most.

• Cellular hub with sensors. The most common type. Yamaha describes the Siren Marine setup as a main device, an app and a subscription, giving battery monitoring, GPS position and geofencing as standard, with wired and wireless sensors added to taste. Garmin's OnDeck kit came with door, temperature and shore-power sensors and a relay switch, and works with or without a chartplotter.
• Satellite. For boats outside cell coverage. GOST advertises satellite tracking that needs no cellular signal, and Siren offers plans with satellite coverage.
• Simple alarm modules. Practical Sailor tested an older cell-based unit about the size of a deck of cards that texted up to three phone numbers when bilge water or battery voltage crossed a limit. Less polished, but often cheaper.
• Engine-data systems. Some hubs also read engine data. Faria Beede says its Sentry works with Mercury SmartCraft, NMEA 2000 and J1939 engines. Don't confuse these with engine apps that work over Bluetooth: Mercury's app, for example, streams live engine data, faults and maintenance reminders through a plug-in SmartCraft Connect module, but Bluetooth only reaches your phone when you're aboard or close by. It's a digital dashboard, not a remote monitor.
• Wi-Fi systems. BoatUS has described monitors that connect through the marina's Wi-Fi, which can cut subscription costs if your marina's signal is reliable at your slip. If the Wi-Fi drops, so do your alerts, so test it.
• Stand-alone trackers. Small GPS trackers with their own battery, some satellite-based, simply text or email you when the boat moves or leaves a geofence. BoatUS mentions one type made for outboard and sterndrive boats that also alerts if the battery dies or the outboard is disconnected, a useful feature where thieves target motors rather than whole boats.

Engine-brand integration has limits. Yamaha's U.S. rigging page lists the Siren 3 Pro as compatible with select digitally controlled Yamaha outboards of 150 hp and up and with Helm Master EX and some older Helm Master systems, adding engine maintenance history and a float plan to the app; it tells owners to confirm compatibility with a Yamaha dealer. A mechanically rigged or smaller outboard can still use the hub for bilge, battery and location, just without the engine data. Check the same way with your own engine maker before paying for an "integrated" package.

Buying used? A monitor that came with a used boat may be an older model built around a cellular network that carriers have since retired. Ask the maker whether the hub still connects before counting on it.

Compare the hardware price, the yearly subscription and which sensors are included before you buy.

A cellular monitor only works where your phone works. Stand at your slip, mooring or storage spot and check your signal. If it's weak, look for a system with an external antenna (Practical Sailor's tester suggested one for poor reception) and mount it high and clear. If the boat goes beyond cell range, or you want tracking offshore, budget for a satellite plan.

The hub must stay powered when you turn the boat off and leave. That means wiring it to the battery side that stays live with the battery switch off, through its own inline fuse at the battery, sized as the maker specifies. Many hubs have an internal backup battery (Garmin listed up to 48 hours for OnDeck), so they can still report after the boat battery dies or someone disconnects it.

Remember the hub itself is a small constant load. On a boat that sits for weeks without a charger or solar panel, check that it won't drain the battery it's guarding (see the parasitic battery drain guide).

Most hubs measure the voltage of the battery that powers them, and some take a second battery input. Set the low-voltage alert high enough to warn you while there's still time to act: a 12-volt lead-acid battery reading around 12.2 volts at rest is roughly half charged (typical; your battery maker's chart rules). A battery that drops overnight while on shore power points to a failed charger or a tripped shore breaker.

Pump activity. A sense wire from the bilge pump's float-switch output (not the manual switch) lets the hub log every time the pump runs. Siren lists bilge run time and daily cycles. This is the early warning: as BoatUS's Don Casey explains, leaks usually start small and grow, and an automatic pump can hide them for weeks. A pump that suddenly runs more often, or longer, is telling you something. BoatUS also notes this method doesn't work with pumps that switch on by themselves every few minutes to check for water.

High water. A separate float sensor mounted above the normal pump-on level catches a failed pump or a leak faster than the pump. BoatUS suggests placing a high-water switch high enough that normal bilge water doesn't set it off, but low enough to warn of real trouble, and checking float switches at least yearly.

Connect sense wires with proper heat-shrink connectors and don't alter how the pump itself is switched (see the bilge pump wiring guide).

A shore-power sensor tells you when dock power drops, whether from a tripped pedestal breaker, a marina outage or someone unplugging your cord. Siren and Garmin both use a plug-in style sensor, so no one needs to open the AC panel. In winter, pair it with a temperature sensor in the cabin or engine room; losing power on a cold night is exactly when you want to know.

Typical options: magnetic reed switches on doors, hatches and lockers; motion sensors in the cabin; and, on some systems, a sensor that replaces one canvas-cover snap and alerts if it's opened. Many hubs can also sound an alarm on board. GOST adds cameras that let you look aboard and confirm what's happening. Hide the hub where a thief won't find it in a minute, and don't advertise the brand with a sticker.

A geofence is a virtual circle around the boat's normal spot. Make it big enough to cover normal movement (a boat swinging on a mooring, a lift going up and down, GPS drift) or you'll get false alarms; small enough that a trailer leaving the driveway triggers it. Know how often your system reports position: Garmin said OnDeck updates every 15 or 30 minutes depending on power, while Faria Beede says Sentry reports every 2 minutes while moving and every 3 hours at rest. A thief can be a long way off before a slow update arrives.

Send alerts to more than one phone: yours, a family member's and, if they agree, a dock neighbor's or the marina office. Write a short plan and keep it in the app or in BoatMend:

• High water: call the marina or a neighbor to check, and call TowBoatUS or Sea Tow if pumping help is needed.
• Shore power lost: ask the marina to reset the pedestal breaker; don't ask a neighbor to handle your shore-power cord in wet conditions.
• Movement or break-in: call the police with the boat's position; don't go yourself.

After installing, lift the high-water float by hand, run the bilge pump, unplug shore power and open a monitored hatch, and confirm each alert arrives on every phone. Repeat at the start of each season and before you leave the boat for a long stretch, like winter or hurricane season.

These systems record where your boat is and when it moves, and some keep data in the cloud (Garmin said OnDeck data was available for 30 days). Before you buy, read the privacy policy: who can see location history, whether it's shared, and how to delete it. Use a strong password and two-step login on the app, and only share access with people you trust. When you sell the boat, remove your account from the hub, cancel or transfer the subscription, and give the buyer the hardware reset so your location history isn't handed over with the boat.

Some hubs can switch things on board from your phone, such as lights, a bilge pump, a fridge or air conditioning. Only use remote switching for loads that are safe to run with nobody aboard. Never use it to run heaters, cooking appliances or anything fuel-burning on an unattended boat.