Why is my boat drawing unusually high power from shore power?
My yacht's shore power meter is showing much higher consumption than usual, even when nobody is aboard. The battery charger and fridge are left on, but I thought everything else was switched off. How do I find what is using the electricity?
Answer
Unusually high shore power consumption usually comes from an unnoticed heater, immersion heater, dehumidifier or battery charger working harder than expected. Switch off the individual AC circuits and watch the meter, then reconnect them one at a time to identify the load before investigating batteries or wiring.
Read the meter correctly
Distinguish power being used now, measured in watts or kilowatts, from energy used over time, measured in kilowatt-hours. A marina meter showing 12 kWh since yesterday tells you something quite different from an onboard display showing 12 A.
On a nominal 230 V supply, a 2 kW heater draws about 8.7 A. A continuous 100 W load consumes 2.4 kWh per day. Several modest loads can therefore run up a substantial bill without approaching the shore connection's current limit.
Record the meter reading and time, then check again after an hour with the boat in its normal unattended condition. Confirm that the marina meter serves your socket and that any onboard reading refers to the AC input. A battery monitor showing 20 A normally means DC battery current, not 20 A from shore.
Find the circuit responsible
Keep panels closed and use the normal switches. Isolate the supply at the pedestal before handling a suspect shore connector or opening electrical equipment, and leave exposed 230 V testing to a marine electrician.
- Switch off the boat's individual AC branch breakers and note the shore meter's instantaneous reading, if available.
- Restore each circuit separately, allowing time for thermostats, compressors and the charger to start.
- On socket circuits, unplug appliances individually to check each appliance's consumption.
- If the marina meter still records significant energy with the boat's main AC breaker off, ask the marina to verify the meter and supply arrangement.
Check the calorifier immersion heater first, followed by cabin heaters, frost protection and dehumidifiers. Immersion elements commonly draw around 500 to 1,500 W, depending on the installation. A thermostat should cycle the element once the water is hot. Repeated hot-water use, a leak or a control fault can keep it running longer.
A fridge may run almost continuously if its condenser is dirty, ventilation is blocked or the door seal leaks. Air conditioning and electric heating can account for most of the consumption.
Check charging and inverter mode
A charger working hard after a discharge is normal. Delivering 50 A at 14.4 V, for example, puts 720 W into a 12 V battery bank. Conversion losses and running DC equipment add to the shore power demand.