Boat sank in Kotka after missing plug let water in, one dead

A missing cooling system plug likely caused a boat to sink near Kotka, killing one person, Finland’s Safety Investigation Authority (Otkes) has found.

The incident occurred on a motorboat with an inboard engine near Kuutsalo. The boat took on water and sank rapidly, trapping one passenger inside. The captain was rescued.

Otkes determined that one of the two drainage plugs in the engine’s cooling system was missing, allowing water to enter. No other possible entry points for water were identified. The boat’s cooling water pump had been serviced about six weeks earlier, and the plugs were confirmed to be in place at that time. The boat had been used for less than three hours since the service.

Investigators believe the plug may have come loose before the trip, letting water into the vessel. Boats with inboard engines are stern-heavy, and if the engine compartment fills with water, they can rise vertically before sinking, making escape difficult. Life jackets or survival suits further complicate exiting through submerged routes, effectively trapping occupants.

In this case, the boat rose vertically before sinking to a depth of about 12 metres. Otkes noted similarities to a 2020 accident involving a Finnish Border Guard patrol boat, which also rose vertically before sinking, trapping one crew member inside.

Otkes has previously recommended that the Finnish Transport and Communications Agency (Traficom) increase awareness among boaters about the dangers of flooding. The authority emphasised that rescuing people from a sinking boat is highly challenging and not always successful. It advised checking the engine compartment and bilges before departure to detect leaks early.

No further investigations into the Kotka incident will be conducted.