Windlass and Bow Thruster Loads with Lithium Batteries
Understand high-current short-duration windlass and thruster loads when designing a marine lithium electrical system.
Windlasses and thrusters are high-current, short-duration loads.
Ask:
- Is the load powered from the house bank?
- Does it have a dedicated battery?
- What is the cable length?
- What is the motor current?
- What is the peak current?
- Does the lithium battery support that current?
- Is the BMS suitable?
- Is the circuit protection suitable?
- Does the manufacturer approve lithium supply?
On larger yachts it may be sensible to keep a dedicated local battery arrangement rather than running extreme current through long cable runs, but the correct solution depends on the vessel.
Turn the appliance into a daily energy figure
The peak wattage tells you whether the inverter and BMS can start the load. Runtime tells you what it does to the battery bank. Treat those as separate checks, then include conversion losses and the loads already running aboard.
- Measure typical watts and realistic hours per day, including standby use and cycling loads.
- Check startup surge and maximum simultaneous current against the inverter, BMS and cabling.
- Test the result against a poor-solar day and preserve a reserve for essential navigation and safety loads.
Work out your own numbers
Inverter DC Current CalculatorWork out the DC current a marine inverter draws from the battery bank, and check it against the BMS continuous and peak ratings before you buy.Battery Runtime CalculatorCalculate how long a marine lithium battery bank will run a given load, down to the state of charge you are willing to reach.
Related pages
Running Starlink from a Marine Lithium BatteryCalculate Starlink power consumption on a yacht and size lithium batteries and solar for Starlink Standard or Starlink Mini.Fridges and Freezers on Marine Lithium BatteriesEstimate daily energy for yacht fridges and freezers and learn how ambient temperature, insulation and duty cycle affect battery sizing.Autopilot and Navigation Power ConsumptionEstimate yacht autopilot, AIS, VHF, chartplotter, radar and navigation loads for offshore lithium battery planning.Laptops, Phones, Tablets and TV on a BoatEstimate digital and entertainment loads for a yacht lithium battery bank and reduce inverter losses with efficient DC charging.Running Induction Cooking from a Marine Lithium BatteryCalculate induction hob energy, inverter current and battery requirements for an electric galley on a sailboat or liveaboard.Running a Washing Machine from Boat Lithium BatteriesPlan battery, inverter, water and generator capacity for running a compact washing machine on a liveaboard yacht.