Boost Fin meets the IPX8 waterproof standard (up to 10m / 32'9").
Each part and component exposed to saltwater are salt fog endurance resistant and certified for saltwater operation. All plugs, connectors, and other electrical contacted surfaces are covered with rubber plugs to prevent them from water.
Seawater can enter the charger port without any damage - there's a diode that essentially acts as a one-way switch for current. It allows current to flow easily in one direction, but severely restricts current from flowing in the opposite direction