Using it well · 6 minute read
Marine autopilot power consumption
Estimate marine autopilot power consumption by drive type. Calculate passage amp-hours and check the effects of steering load, cable losses and low voltage.
Ask five owners what their autopilot draws and you will get five numbers, all of them right for their boat on the day they measured. Autopilot consumption depends on the drive, the sea state, the balance of the boat and the gain setting far more than on the brand. This guide gives working ranges and a calculator so you can plan a Bass Strait or Coral Sea passage without guessing.
Key facts
- Tiller pilot
- 0.4–1 A average; 2–3 A peaks
- Wheel pilot
- 0.5–1.2 A average; 4 A peaks
- Linear drive
- 1–3 A average; 10 A peaks
- Hydraulic pump
- 1–2 A average on a power boat; 8–20 A peaks
- Racing pilot
- 3–5 A average under spinnaker
- Windvane
- 0 A
Factors affecting autopilot current draw
An autopilot draws almost nothing while it is thinking and a lot while it is moving the rudder. Average consumption is therefore about how often and how far the drive moves. On flat water with a balanced boat the drive barely moves; in a quartering sea with too much sail up it works constantly. Gain and response settings decide how eagerly it chases every yaw; higher settings cost amps.
Voltage matters too. A drive fed through thin, corroded cable sees a lower voltage, draws more current for the same work and may trip low-voltage alarms while the batteries are still fine at the terminals.
Working figures by drive type
Cockpit tiller pilots on a balanced boat average 0.4–0.8 A and rise above 1 A when working hard. Above-deck wheel drives are similar. Below-deck linear drives on a 10-tonne cruising yacht average 1–3 A under sail and a little less under power on flat water. Hydraulic pumps on a planing power boat average 1–2 A because they rest between corrections, with short peaks of 8–20 A. Racing pilots driven hard under a spinnaker can average 3–5 A and more.
Multiply by hours to get amp-hours. A cruising yacht at 2 A for 24 hours is 48 Ah, which on a 400 Ah lithium bank is manageable and on a 200 Ah lead-acid bank is a third of the usable capacity.
- Coastal day sail, 8 hours, wheel pilot: about 8 Ah
- Sydney to Port Stephens overnight, 20 hours, linear drive: 30–50 Ah
- Bass Strait crossing, 40 hours, linear drive in a seaway: 80–120 Ah
- Brisbane to Whitsundays trade-wind week, 6 days at sea, linear drive: 250–400 Ah total
- Offshore fishing day, 10 hours, hydraulic pump: 10–20 Ah
View as a table
| Item | Low | High |
|---|---|---|
| Cockpit tiller pilot | 0.4 A | 1 A |
| Above-deck wheel pilot | 0.5 A | 1.2 A |
| Below-deck linear drive (cruising yacht) | 1 A | 3 A |
| Hydraulic pump (planing power boat) | 1 A | 2 A |
| Racing pilot under spinnaker | 3 A | 5 A |
| Windvane self-steering | 0 A | 0 A |
Cable sizing and voltage drop
Drives are sensitive to voltage drop because they draw high peak currents. Manufacturers specify cable size by run length; follow it, and measure the voltage at the course computer with the drive working. A 10 per cent drop is a problem. Run the supply from the house bank through its own breaker, not from an instrument circuit.
Reducing autopilot power consumption
Balance the boat: reef earlier, ease the main, trim for neutral helm. Turn response down when the sea allows. Steer to wind rather than compass on long reaches so the pilot is not fighting the sails. Keep the drive lubricated and the belt tensioned. On passages, alternate the electronic pilot with a windvane if you carry one.
Low voltage behaviour
Planning an Australian passage
Work out the hours, pick a realistic average for your drive in the expected sea state, and add 30 per cent. Compare that with the usable capacity of the bank and the daily input from solar, wind and engine. Tasmanian winter solar is a fraction of Queensland winter solar; the calculator below lets you set the inputs. If the numbers do not close, the answers are a bigger bank, more generation, less pilot use, or a windvane.
Passage energy calculator
- Pilot draw per day
- 48 Ah
- Pilot draw, whole passage
- 96 Ah
- Usable bank
- 150 Ah
- Solar + engine input per day
- 107 Ah
Autopilot-only energy estimate
Net gain of 59 Ah per day from the autopilot alone, before lights, fridge and instruments. After 2 days the estimated usable reserve is 150 Ah of 150 Ah usable. This assumes a full usable reserve at departure; surplus charging cannot exceed battery capacity.
Autopilot-only estimate, not a whole-boat endurance forecast. Charging timing, battery acceptance and other loads are excluded. Working figures only. Typical amps are averaged draws; peaks are far higher. Solar assumes a 70 per cent system efficiency; alternator assumes 60 per cent of rated output. Measure your own boat with a shunt-based monitor on a real passage.
Questions
Frequently asked
Does a bigger autopilot use more power?
Not necessarily. A correctly sized below-deck drive makes fewer, more efficient corrections than an overworked tiller pilot and can use less energy on the same boat in the same sea.
Can solar alone run an autopilot?
On a cruising yacht with 400 W or more of solar in northern Australia, comfortably in summer. In southern winter, no. Plan on engine or wind generation as well.
Will lithium batteries help?
Lithium gives more usable capacity and holds voltage under load, which drives like. It does not reduce what the pilot draws.
Practise autopilot operation with an instructor
Habits are learned at the helm with someone watching. The training section explains what a good instructor covers and where to find one in your state.