Autopilot Drive Types: Linear, Rotary, Hydraulic

The Drive Unit: The Part That Moves the Boat's Steering

An autopilot system has a control head, a heading sensor, a course computer, and a drive unit. The drive unit is the physical component that connects to your boat's steering system and moves it when the autopilot sends a command. Without a matching drive, the autopilot cannot steer the boat, no matter how advanced the electronics are.

Drive units come in three broad categories: linear drives, rotary drives, and hydraulic pumps. Each works with a different kind of steering system. Raymarine's drive unit page describes this as "the part that interfaces with your vessel's steering system," and the company produces drives for mechanical, hydraulic, and power-assisted stern drive systems.

The right drive for your boat is determined by the steering already aboard. This article explains the three drive types and how to match one to your steering system. For a broader overview of autopilot systems, see the best marine autopilot guide.

Linear Drives: Push and Pull the Steering Linkage

A linear drive is a mechanical actuator that extends and retracts a rod or shaft. It is typically connected to a tiller, a rudder post, or a mechanical steering link. When the autopilot moves, the rod pushes or pulls, turning the rudder or outboard.

Linear drives are most common on sailboats with tiller or wheel steering that is not hydraulic. They are also used on some small powerboats with cable steering. Raymarine's Type 1 Linear Drive Unit is described as a "mechanical linear autopilot drive for boats up to 11,000 kg (24,000 lbs) displacement" on the maker's drive unit page.

A linear drive does not contain its own fluid. It relies on a motor and a reduction gear to move the rod. The length of the stroke and the mounting arrangement are set by the manufacturer for different boat sizes. Before choosing a linear drive, you need to know the steering system's geometry and the maker's specified boat size range. If you are looking for a complete system, the best complete autopilot packs guide can help.

• Linear drives suit tiller-steered sailboats and some wheel-steered boats with mechanical linkage.
• The drive rod attaches to the steering arm or tiller, not to a hydraulic cylinder.
• Raymarine's Type 1 linear drive lists a maximum boat displacement of 11,000 kg (24,000 lbs).

Rotary Drives: Turn the Steering Shaft

A rotary drive produces rotational motion to turn a wheel, a steering shaft, or a pinion that engages the steering gear. Instead of pushing a rod, it rotates a shaft. Rotary drives are commonly used on sailboats and powerboats with mechanical steering systems where the wheel turns a cable or a direct shaft.

Raymarine offers Type 1 and Type 2 rotary drives. The Type 1 Rotary Drive is rated for vessels up to 11,000 kg (24,000 lbs) displacement, and the Type 2 Rotary Drive is rated for vessels up to 20,000 kg (44,000 lbs) displacement, according to the manufacturer's drive unit page. These figures are given as maximum displacement, not as a recommendation for a specific boat; you should confirm your boat's displacement against the maker's information.

Rotary drives are distinct from linear drives because they provide torque to a rotating shaft, not a straight push. They are often used where a wheel pilot would be too small or where a below-decks connection is needed. For boats with wheel steering, the best autopilots with control head guide offers options.

• Rotary drives turn a shaft, not a rod.
• They are for boats with mechanical steering that already uses a rotating element.
• Raymarine lists Type 1 rotary up to 11,000 kg and Type 2 rotary up to 20,000 kg displacement.

Hydraulic Pumps: Power the Hydraulic Steering System

A hydraulic pump drive is not a mechanical rod; it is a pump that adds or removes hydraulic fluid in a boat's hydraulic steering system. When the autopilot commands a turn, the pump pressurizes one side of a hydraulic cylinder, which moves the rudder or outboard. Hydraulic pumps are used on powerboats and larger sailboats that have hydraulic steering.

Raymarine's lineup includes Type 0.5, Type 1, Type 2, and Type 3 hydraulic pumps. These are matched to the steering system's displacement, not the boat's length. The maker's drive unit page gives steering cylinder volumes: Type 0.5 for 50 to 110cc (3.1 to 6.7 in³), Type 1 for 80 to 230cc, Type 2 for 230 to 350cc, and Type 3 for 350 to 500cc.

If your boat has hydraulic steering, a hydraulic pump is the typical drive. It attaches to the hydraulic lines, not to a linkage. The pump's flow and pressure must match the steering cylinder's volume, which is why the maker provides those cc ranges.

Hydraulic pump drives are available as standalone units or included in autopilot packs. For example, Raymarine's power pilot packs are described as autopilots for boats with hydraulic steering (like the EV-100 Power Pilot and EV-200 Power Pilot). For a selection of hydraulic autopilots, see the best hydraulic autopilots guide.

• Hydraulic pumps are for boats with hydraulic steering systems.
• The pump must be sized to the steering cylinder's volume, given in cc or cubic inches.
• Raymarine lists four hydraulic pump types, from Type 0.5 to Type 3.

Matching the Drive to the Steering System

The first step is to identify how your boat steers. If you are unsure, check the boat's manual or look at the steering mechanism at the helm. A hydraulic steering system has a hydraulic fluid reservoir and hoses leading to the rudder or outboard. A mechanical system uses cables, rods, or a direct shaft. A tiller is a straight arm attached to the rudder.

Once you know the steering type, choose the drive category that matches it. Tiller and mechanical steering often use linear drives. Wheel steering with a mechanical shaft can use a rotary drive. Hydraulic steering requires a hydraulic pump. This is not an exact rule for every boat, but it is the way autopilot manufacturers categorize their drives.

The maker's drive unit page is the authoritative reference. For Raymarine, the drive unit selection guide specifically asks you to "consult an authorized Raymarine dealer" if you cannot determine your steering system. The same principle applies to any brand: rely on the manufacturer's guidance, because the fit depends on the boat's specific steering hardware.

It is also important to note that some autopilot packs include the drive while others do not. Core packs omit the drive, leaving you to choose a compatible drive separately. That is why understanding drive types helps you select a complete pack or a core pack plus a drive. If you are considering a core pack, the best autopilot core packs guide explains what to look for.

• Identify the steering type: tiller, wheel, cable, or hydraulic.
• Linear drives are for mechanical push-pull steering.
• Rotary drives are for rotating shafts.
• Hydraulic pumps are for hydraulic steering systems.
• When in doubt, contact the autopilot maker or a qualified dealer.

How Drive Units Appear in Autopilot Packs

Autopilot packs are often named by the type of drive they include. For example, Raymarine's product line includes the EV-100 Tiller Autopilot, the EV-100 Wheel Pilot, and the EV-100 Power Pilot. The Power Pilot is for "small powerboats with hydraulic steering," according to Raymarine's autopilot packs page. These names tell you which drive type is in the box.

Complete packs include a control head, a course computer, a heading sensor, and a matching drive. Core packs contain the electronic components but leave out the drive. If you choose a core pack, you must buy a drive separately, and it must match your steering system. This is where the drive type matters most.

When you see a listing that says "no drive" or "requires pump," it is a core pack. A complete pack will name the drive type, such as "linear drive included" or "hydraulic pump included." Read the bullet list in the listing to confirm which drive is supplied.

If you already have a drive from an older autopilot, you might keep it and buy a core pack, but only if the older drive is compatible with the new electronics. The maker's page or a dealer can tell you. For more on this, see the article on core packs vs complete packs.

What to pick for your situation

Questions

Which autopilot drive type is best for a sailboat?

It depends on the steering system. Tiller-steered sailboats often use a linear drive or a tiller pilot. Wheel-steered sailboats might use a rotary drive if the steering is mechanical, or a hydraulic pump if it is hydraulic. The maker's drive selection page is the definitive guide.

Can I use a hydraulic pump drive on a boat with cable steering?

No. A hydraulic pump requires a hydraulic steering system to move the rudder. Cable steering uses mechanical linkages, so you need a linear or rotary drive instead. Check your steering type before choosing a drive.

What does "requires pump" mean on an autopilot listing?

It means the pack is a core pack and does not include a hydraulic pump drive. You must buy a compatible hydraulic pump separately. The listing will usually state the required pump type or ask you to consult the maker's manual.

How do I know which drive size to choose?

For hydraulic pumps, the size is matched to your steering cylinder's volume. For linear and rotary drives, the maker gives a boat displacement range. These numbers appear on the manufacturer's drive unit page. Use those figures as the first check, and ask a dealer if you are still unsure.

Can I keep the drive from my old autopilot when upgrading?

Sometimes. If the drive is a linear or rotary unit that matches your steering and is compatible with the new course computer, you might keep it. The maker's page or a dealer will confirm compatibility. If not, buy a new drive with a core pack.