69% of boats sink at the dock: keep an eye on yours this winter

During winter storage, your boat stays unattended in the marina for months. Sense4Boat sensors keep watch on board, 24/7.

Every year, the same scenario unfolds. The warmer days come to an end, your boat returns to its berth or is hauled out, and you get back to life ashore — often dozens, sometimes hundreds of kilometres from the marina. For four to six months, your boat will be on its own. And that is precisely when problems can arise.

A cracked through-hull fitting, a failed bilge pump, a damaged sterndrive bellows: a few hours can be enough for a boat to sink at its berth. And that is not the only winter risk. A battery left partially discharged can suffer irreversible sulphation within weeks. An unexpected freeze can crack pipes, valves and water tanks. These are silent problems, invisible from your living room — and ones you may only discover in spring, when it is time to launch again.

The good news is that simple, self-contained and affordable solutions are now available to help you keep an eye on your boat throughout winter storage. At Advanced Tracking, we distribute Sense4Boat connected sensors in France: a range of three sensors designed specifically for monitoring leisure boats. Here is how they work, and how they can change your next winter lay-up.

The three risks your boat faces during winter

Before discussing technology, let us look at the practical threats to a boat left unused between October and April. Three risks account for the vast majority of winter claims.

Water in the bilge: sinking at the dock is more common than you might think

A boat does not have to be at sea to sink. Every hull has numerous potential points of water entry: engine cooling systems, sanitary outlets, through-hull fittings and stern glands. An ageing seal, a cracked bellows or a failed bilge pump can be enough to let water accumulate. With nobody on board to notice, a boat can sink within hours — even at its berth in a monitored marina.

Beyond outright sinking, the slow accumulation of rainwater or condensation in the bilge encourages mould, corrosion of electrical equipment and deterioration of materials. This damage often goes unnoticed and can cost several thousand euros to repair.

Batteries: sulphation, a silent and irreversible enemy

Marine batteries are expensive and often last only a few seasons. The main cause of premature failure is not wear, but poor winter storage. The golden rule is simple: a battery should always be stored fully charged. When it spends the winter partially discharged, a chemical process occurs: lead sulphate crystals build up on the plates and irreversibly reduce the battery's capacity. This is sulphation.

The longer the battery remains discharged, the more crystals accumulate. In spring, you may discover that your battery bank is unusable — despite manufacturers quoting a service life of 7 to 10 years for properly maintained batteries. A shore power charger outage, a blown fuse or a parasitic load can be enough to start the process without anyone noticing.

Freezing temperatures: rapid damage that insurance rarely covers

The outdoor temperature does not always reflect conditions inside the boat. An unexpected freeze can irreversibly damage pipes, valves, freshwater tanks and cooling systems. Insurers make it clear: frost damage during winter storage resulting from inadequate preparation is generally not covered by insurance policies^[2]. In other words, you will be left with the bill.

Conversely, the engine room of a motorboat also contains heat-sensitive equipment — chargers, batteries and solar charge controllers. Overheating during a charging cycle can be an early warning sign of fire. Conventional smoke detectors do not operate above 55 °C and are not designed for the damp conditions of an engine room.

Sense4Boat: three sensors to address the full range of winter risks

The Sense4Boat platform was designed specifically to address these three risks. The principle is simple: three self-contained sensors, each dedicated to a particular risk, monitor your boat 24 hours a day and alert you immediately when an anomaly is detected — wherever you are.

Unlike GPS tracking systems that locate your boat, Sense4Boat monitors what is happening inside: water in the bilge, battery voltage and equipment temperature. It is the natural complement to a location tracker, not a competitor.

The bilge sensor: your lookout for water ingress

The bilge sensor continuously monitors the water level in your bilge using two marine-grade floats mounted on 3-metre cables. Install them at your chosen height — for example, one float in the engine bilge and another in the forward bilge — to monitor two separate areas with a single sensor. As soon as a float detects an abnormal water level, an alert is sent immediately. The sensor also performs a self-diagnostic check every 12 hours and confirms that it is working correctly: you know that silence means “all is well”, rather than “the sensor has failed”.

The battery sensor: no more unwelcome surprises in spring

The battery sensor connects directly to the terminals of two independent battery banks (12 V or 24 V) using the supplied 3-metre cables with protective fuses. It continuously monitors voltage and alerts you as soon as a low or critical voltage is detected — before sulphation takes hold. It also monitors charging cycles: you are informed when each charge starts and finishes, and alerted if an anomaly occurs. If your shore power charger is disconnected or fails in January, you will know that same day, not in April.

The temperature sensor: fire detection and frost protection

The temperature sensor has two independent probes on 3-metre cables, with a measurement range of −55 °C to +125 °C and an accuracy of ±0.5 °C. Readings are taken every 30 seconds. Place one probe in the engine room to detect any abnormal rapid temperature rise — an early indication of a developing fire — and the other near the water systems to receive an alert when freezing threatens. You define your own alert thresholds in the app: low, high and critical temperatures, and the maximum rate of temperature rise.

Why these sensors work where other systems fail

Three design choices make all the difference for winter use.

Five years of battery life, without drawing power from the boat. Each sensor runs on its own replaceable batteries and does not use the boat's electricity. No wiring into the onboard electrical system and no risk of draining your boat's batteries — which would be ironic for a system intended to protect them. This also makes installation accessible to anyone: allow less than 15 minutes per sensor, with no technician required.

NB-IoT, designed for challenging environments. The sensors communicate using NB-IoT (Narrowband IoT), a long-range, ultra-low-power cellular technology. In practice, the signal penetrates fibreglass or steel hulls, works in areas with weak coverage — such as dry docks or winter storage sheds — and consumes ten times less energy than a conventional 4G connection. If the boat sails beyond network range, an internal buffer stores readings and transmits them as soon as connectivity returns. No data is lost.

Alerts that actually reach you. When an anomaly is detected, you do not just receive a notification buried among others. The system simultaneously triggers an automated voice call (which rings even when your phone is on silent), an SMS, a push notification and a detailed email. Your emergency contacts are notified at the same time. If your marina is a Sense4Boat partner, the marina office can also receive the alert and take direct action on your boat while you are away — often making all the difference.

What actually happens when a problem arises?

Imagine a January night. Torrential rain hits the marina. Your ageing bilge pump can no longer remove the accumulating rainwater. At 3:12 am, the float on your bilge sensor detects the abnormal level. At 3:13 am, your phone rings: a voice call informs you of the situation, followed by an SMS identifying the sensor concerned. You call the marina office or a friend nearby, who takes action before the water reaches the electrical equipment. The cost of the incident: replacing a bilge pump. Without a sensor, you might have discovered a boat full of water in spring — or worse, one sunk at its berth.

The same principle applies to batteries: a “low voltage” alert in December gives you time to act — recharge remotely if your installation allows it, or ask your service provider to intervene — before sulphation permanently damages your battery bank.

How much does a winter of peace of mind cost?

Let us do the maths. A Sense4Boat sensor costs between €269 and €281, with the first year of cloud subscription included. Renewal then costs €63 per year per sensor — less than 18 euro cents a day for continuous, 24-hour monitoring with unlimited multi-channel alerts.

Compare that with replacing a sulphated battery bank, which can cost hundreds and often thousands of euros. Repairs following water damage or frozen systems also run into thousands of euros — not to mention that winter damage caused by inadequate preparation is frequently excluded from insurance policies^[2]. Preventing a single incident can pay back the investment several times over.

You can start with a single sensor — the bilge sensor is the most broadly applicable — and expand your setup over time. All sensors are managed through the same mobile app, available on iOS and Android.

Prepare for winter storage now

September and October are the best months to equip your boat: install the sensors while preparing for winter storage, test the alerts while you are still nearby, and leave with peace of mind.

Our boating experts, based in Hyères opposite the marina, are available to recommend the right combination of sensors for your boat and winter storage arrangements — afloat, out of the water or in a storage shed.

FAQ — Winter storage and connected monitoring

▶ Watch the Sense4Boat video on YouTube

References

[1] As Weather Wreaks Havoc, Better Check Your Boat's Insurance Policy — IYBA / BoatUS: “69% of sinking claims occur while the boat is moored at the dock and the owner is away.”

[2] How to Avoid the Three Most Common Boat Insurance Claims — Aviva: “Damage caused by inadequate preparation for winter is normally not covered by your insurance policy.”