Selecting your Raymarine Drive Unit

14 July 2022

Selecting your Raymarine Drive Unit

At their most basic level a marine autopilot is made up of brains and muscle. With Raymarine Evolution autopilots the brain lives inside the EV-1 sensor core. To transfer the brain power into steering it needs to be matched up to some muscle in the form of an autopilot drive unit. 

The autopilot drive unit provides the muscle needed to steer your boat and keep you on the right course. The exact type of drive unit you will need depends on a few factors including the type of steering system your boat is fitted with, and the displacement of the boat. 

Raymarine’s Evolution autopilot systems accommodate vessels with hydraulic steering, mechanical steering as well as power assisted stern drive systems. We have a broad range of drive units to match almost any type of steering system.  

Hydraulic Steering Systems 

Boats with traditional hydraulic steering will normally use a reversing hydraulic pump, matched to the capacity of the hydraulic steering system. Raymarine offers pumps of different flow-rates to best match the volume of the hydraulic steering system. This ensures that when under autopilot control the boat will steer with confidence and not respond too quickly, or too slowly to steering orders. 

If your boat has hydraulic steering the first thing you’ll need to find out is the capacity of the hydraulic steering cylinder or ram(s) that move your motors or rudder. If you have a newer boat this information can often be found in your boat’s Owner’s Manual or steering system documentation. Another place you can usually find this is on the steering ram itself. Most systems have a metal or printed manufacturer’s data plate attached. The volume of the cylinder will be stated either in cubic inches or cubic centimeters. If your data plate does not list a volume them make a note of the manufacturer’s name and the cylinder model number. Raymarine dealers can cross-reference this information to determine the volume of your steering ram. 

Once the volume is known you can match it up to the specifications of each pump size offered by Raymarine.   Each pump fits a range. Choose the pump that covers the volume of your system. Do not move up or down in the range as it offers no performance improvement, and can make the boat steer poorly.

Hydraulic Linear Drives 

Designed for larger mechanically steered vessels over 20,000kg, our hydraulic linear drives are self-contained hydraulic steering systems consisting of a reversing pump, reservoir, and hydraulic ram. 

A hydraulic linear drive unit connects to the rudder stock via an independent tiller arm. Accessory fittings from your steering system manufacturer may be required. An electromagnetic clutch mechanism in the ram allows the autopilot to be disengaged when hand-steering the boat.    

One important prerequisite for using a hydraulic linear drive is your steering system must be capable of being back-driven. That is, when a force is applied to the rudder or rudder stock, that force should be able to be transferred into motion of the cables or mechanisms that lead back to the helm. 

Hydraulic Liner Drive systems can generate a tremendous amount of thrust and must be properly installed to prevent damage to the boat’s hull, structural members and steering components. We strongly recommend consulting with an authorized Raymarine dealer or experienced boat yard when installing one of these drive units.

Mechanical Linear Drives 

Boats with mechanical steering systems like sailboats and some powerboats can use a mechanical linear drive system. Raymarine mechanical linear drives provide powerful thrust, fast hard-over times, and quiet operation. Mounted below decks, the linear drive moves the rudder directly by pushing the tiller arm or a rudder quadrant.  These drive units are powered by an electric motor that operates a push/pull linear drive system through a gearbox that creates mechanical advantage. These systems also have an electromagnetic clutch that allows the drive to freewheel when the boat is under hand-steering.

A linear drive unit connects to the rudder stock via an independent tiller arm. Accessory fittings from your steering manufacturer may be required, and you must be able to back-drive steering system from the rudder.  Similar to the hydraulic linear drive systems, these mechanical linear drive systems are also capable of generating tremendous amounts of force when in operation. Improper installation can result in severe damage to the boat’s hull, structural members or the steering system. We recommend consulting with an authorized Raymarine dealer or experience boat yard when installing one of these drive systems.

The exact linear drive you’ll need will be determined by the fully laden displacement of your boat, and its power system. Larger, heavier boats will require a larger drive system. We offer a range of drives to fit boats of varying weights with 12V or 24V DC power systems.


Mechanical Rotary Drives 

The rotary drive is another electrically driven autopilot drive that engages with the boat’s mechanical steering system through a chain and sprocket interface. When engaged the rotary drive’s sprocket drive engages with the boat’s steering to keep it on course. When in standby, an electromechanical clutch disengages the rotary drive for easy hand-steering. The design of the Raymarine rotary drive unit provides smooth, powerful autopilot-controlled steering with quiet operation. 

The exact rotary drive you need will be dependent of the fully-laden displacement of your boat and its power system. Heavier boats require a heavier-duty drive system, and we offer drives for both 12 volt and 24 volt DC systems. 

When planning for a rotary drive installation you will need to inspect the boat’s current steering chain setup to determine where the drive will be situated, and what size drive sprocket will be needed to interface it into the boat.

Stern Drives 

Raymarine also offers Stern Drive autopilot actuators that works with many popular inboard/outboard (I/O) propulsion systems from Volvo Penta, Mercruiser, Yamaha and OMC that utilize power assisted steering. This electrically-actuated drive unit installs along the gunwhale or transom of the boat and works directly with the I/O drive’s steering actuator.

What’s Next? 

Once you have the proper drive unit for your boat selected, you’ll match that drive unit up to a compatible Evolution autopilot Actuator Control Unit (ACU). The ACU provides power to the drive unit, and also interfaces with the other pilot components including the EV1 sensor core, control heads, chart plotters, instruments, etc. 

Learn More

Check out each drive unit's product page to see more details and specifications.