How do I safely switch a boat from shore power to its generator?

Switch off the AC loads, isolate shore power, then start and check the generator before selecting it through the boat's fitted transfer switch. Restore appliances one at a time, ensuring shore power and generator power can never feed the same circuit together.

Check the source selector

Find the AC source selector and identify its positions before touching anything else. A manual installation usually has SHORE, OFF and GENERATOR positions; other boats use interlocked breakers or an automatic transfer switch controlled from a display.

The transfer arrangement must disconnect one source before connecting the other. Never combine supplies by operating independent breakers unless the installation has a proper interlock. Backfeeding can energise the shore connection and damage equipment.

Some boats have separate selectors for domestic services and air conditioning. The Swift Trawler 47, for example, can have separate source selectors for these circuits, so changing the domestic supply does not necessarily change the air-conditioning supply.

If the labels are unclear, the selector is damaged or the interlock appears to be missing, have a marine electrician identify the arrangement before proceeding. Do not open or work inside an energised AC panel.

Disconnect shore power

Use this sequence for a conventional manual selector installation. Follow the boat's instructions where automatic controls handle the transfer.

1. Switch off air conditioning, immersion heater, cooker and other heavy AC appliances, then switch off their branch breakers. Include the battery charger so it cannot immediately demand a large load.
2. Turn off the boat's shore-power main breaker and put the source selector in OFF.
3. If removing the shore lead, turn off the pedestal breaker, unplug at the pedestal first, then disconnect at the boat and close the inlet cap.
4. Stow the lead clear of water, damage and moving machinery.

The lead can normally stay plugged in while the generator runs, provided a correctly installed transfer system isolates the shore supply. Unplugging is sensible when leaving the berth and makes the disconnection obvious, but it does not replace a proper transfer switch.

Start and check the generator

Check the fuel level, engine oil and coolant where applicable. Make sure the generator's seawater inlet seacock is open. Check its starting battery isolator and run the compartment ventilation as specified. On a Swift Trawler 47, the generator draws fuel from the port tank and has its own 12 V starting circuit.