Autopilot Drive Current Draw: What to Expect

What drive current draw means on a listing

Every autopilot system ends in a drive, the motorized part that actually moves the steering. When the autopilot makes a course correction, the drive's motor runs and draws electrical current from the boat's battery. That draw is expressed in amperes, usually shortened to amps, and it is a stated detail on the maker's specification sheet, not a number a listing can invent.

When you read a listing for a complete autopilot pack or a core pack, the drive is named in the title: linear, rotary, or hydraulic pump. Each drive type has its own motor and its own current draw, and the maker's page for the drive is the authoritative source for the figure. The drive types article explains how these names work.

Why the figure matters for your electrical system

Your boat's electrical system is shared: the drive, the control head, the chartplotter and the bilge pump all pull from the same battery bank. If the drive's current draw is higher than the circuit is designed for, you can see voltage drop, slow steering movement, or tripped fuses. Sizing the wire and the fuse is an installation task, and the maker's manual and a qualified installer are the ones who decide it.

The practical way to use the figure is as a planning number. When you ask for an installation quote, the installer will want the drive type and its specified current draw so the power circuit can be sized correctly. This is why the marine autopilot guide compares packs on stated details only: the current draw is a number the maker publishes, and you read it from the specification. On a boat with a networked helm, the same battery feeds the network devices, and the NMEA 2000 article explains how the network carries data and status. An autopilot does not replace a lookout: the U.S. Coast Guard Boating Safety page covers the operator's responsibility to keep watch and to complete a boating safety course.

Linear drives and their motor draw

A linear drive is a mechanical actuator that pushes or pulls a rod connected to the steering. The motor runs during each correction, draws current while it runs, then stops. The specification sheet for the linear drive lists the motor's current draw in amperes, and that is the figure you plan around.

When you compare linear drives, the stated details that matter are the drive type, the boat fit published by the maker, and the current draw in the specification. The sailboat autopilot guide and the complete pack guide both name the drive in the listing so you can find the matching specification.

Rotary drives and their motor draw

A rotary drive turns a shaft or a wheel instead of pushing a rod. It is common on wheel-steered sailboats and some powerboats. Like the linear drive, its motor runs during corrections, and its current draw is listed in the maker's specification.

Rotary drive names follow the maker's model line. The Raymarine drive units page, for example, names Type 1 and Type 2 rotary drives and describes them as electric rotary autopilot drives. The same page lists the drive units for each steering system type, which is where the current draw specification lives.

Hydraulic pump drives

On boats with hydraulic steering, the autopilot drive is a hydraulic pump that moves fluid through the steering lines. The pump's motor draws current whenever the autopilot corrects the course, and the specification sheet for the pump lists its current draw. The hydraulic autopilot guide compares complete and core packs for hydraulic steering.

A hydraulic pump is a motor just like a linear or rotary drive, so the same electrical-planning logic applies. The circuit must be sized for the pump motor's stated draw. The hydraulic versus linear article explains the difference between these two drive families, and the voltage system article covers the 12-volt versus 24-volt question.

Rated current draw versus average draw

Current draw is not constant while the autopilot is engaged. The motor draws more when it starts moving the steering and less once the move is underway, and the autopilot only corrects when the boat drifts off its intended heading. The figure on the specification sheet is the rated draw for the drive, and that is the number you use for planning the circuit.

Average draw over a voyage depends on how often the autopilot corrects, which varies with conditions. Do not try to estimate an average yourself. The rated figure is the conservative planning number, and the installer uses it together with the maker's manual to size the wiring and the fuse.

What to look for in the specification

The current draw figure is one of several stated details that belong together in a specification. Read the drive type, the power usage, and the boat fit as a set, and treat anything missing as a question for the seller.

• Compare the drive type first: linear, rotary, or hydraulic pump, as named on the listing.
• Read the power usage entry on the maker's page. The Furuno NavPilot 300 page, for example, lists power usage of 12-24 VDC.
• Confirm the current draw figure is present in the specification sheet. If the listing does not state it, treat it as not stated by the seller and ask the maker or a dealer.
• Check the boat fit published by the maker, because a drive must suit the steering system and the boat.
• Discuss the electrical plan with a qualified installer before ordering any pack.

Questions to ask before you buy

The current draw figure only helps if you read it in context. These are the questions that connect the specification to your boat.

• What drive type is in the pack, and what current draw does the maker's specification list for it?
• Does the pack include a drive, or is it a core pack that keeps your existing drive?
• What voltage system does the drive run on?
• Who sizes the wiring and the fuse, and does the maker's manual cover it?
• What spare parts are available for the drive?

What to pick for your situation

Questions

What is drive current draw?

It is the electrical current, in amperes, that the drive's motor takes from the battery when it moves the steering. The maker's specification sheet lists the figure for each drive type.

Is a higher current draw a problem?

It is not good or bad by itself. The drive must suit the steering and the boat, and the circuit must be sized for the stated draw. An installer uses the specification to plan the wiring.

Where do I find the current draw figure?

In the maker's specification sheet for the drive. The listing may not state it, so ask the maker or a dealer if it is missing.

Do I need to compare current draw across drives?

Only as one stated detail. The boat fit and the drive type matter first, and the current draw is the planning number for the electrical circuit.

Does the control head draw current too?

Yes, every component in the system draws current, but the drive is usually the largest load because it is the part that moves the steering. The control head's draw is also in its specification.