Rotary vs Hydraulic Autopilot Drives

What a drive unit does

An autopilot drive is the part of a marine autopilot that connects to your boat's steering. Raymarine describes the drive unit as "the part that interfaces with your vessel's steering system." The drive is what actually moves the helm (the wheel, the rudder or the steering ram) once the autopilot decides how to steer.

Because the drive must physically connect to what you already have aboard, the drive choice follows the steering type, not the other way around. A boat with hydraulic steering calls for a hydraulic pump drive. A boat with cable or mechanical steering calls for a rotary or linear drive. This is why listings name the drive in the pack title, and why this site lets you filter by drive in the box.

Hydraulic autopilot drives

A hydraulic autopilot drive is a pump that moves fluid in a hydraulic steering system. It connects to the same hoses that run from your helm to the steering ram. When the autopilot commands a turn, the pump pressurizes one side of the system and relieves the other, so the steering moves as if you were turning it yourself.

Raymarine names its hydraulic pumps with type numbers (Type 0.5, Type 1, Type 2 and Type 3) and describes each as an "autopilot drive for boats with hydraulic steering." The type number is a class name that tells you which hydraulic steering systems the pump is sized to serve. The maker's page for each pump states the steering system range, so the type number is only a label on a listing.

Hydraulic drives are common on powerboats, because many powerboats steer hydraulically. They are also used on some sailboats with hydraulic steering. If your boat has a helm pump and steering hoses, a hydraulic pump drive is the one that matches your steering. See the hydraulic autopilot guide for listings that include a pump.

Rotary autopilot drives

A rotary autopilot drive is an electric drive that turns a mechanical steering system with a rotating output. It mounts near the steering and works through the boat's existing mechanical linkage (for example a chain, belt or gear that turns the wheel or rudder). "Rotary" describes the motion: the drive output rotates to move the steering.

Raymarine offers Type 1 and Type 2 rotary drives, both described as "electric rotary autopilot drive" units. As with the hydraulic pumps, the type number is a class name; the maker's page states the steering systems the drive matches. Rotary drives suit boats with mechanical steering, which includes many sailboats with wheel steering and some powerboats with cable steering.

The turning force a rotary drive applies is called torque. In general terms, torque is the force that rotates the steering linkage. Listings do not state a torque figure you can compare across brands, so the practical question is whether the drive is made for your steering type, which the maker's page decides. Read more in the sailboat autopilot guide if your boat steers mechanically.

Your boat's steering decides the drive

Before choosing between a rotary and a hydraulic drive, find out what steering your boat has. Hydraulic steering uses fluid and a helm pump; mechanical steering uses cables, a chain or a belt. The autopilot listing may say "hydraulic," "rotary," "linear" or "tiller" in the drive name; that word is the clue to which steering it connects to.

If you are not sure, the maker's guidance is to ask. Raymarine's drive unit page says that if you do not know how to determine the steering system installed on your vessel, you should consult an authorized dealer or contact the maker. The same advice applies to any brand.

Choosing a drive is never about picking the physically larger option. The drive has to match the steering that is already aboard. A hydraulic pump cannot drive a cable-steered wheel, and a rotary drive cannot move a hydraulic ram. See which drive types fit your steering for a fuller explanation.

Reading a drive name on a listing

Listings carry drive names that tell you what is in the box. A title like "Type 1 Hydraulic Pump" means the pack includes a hydraulic pump drive; "Type 2 Rotary Drive" means it includes a rotary drive. When a title says a pack is "no drive" or "requires pump," it means the electronics are included but the drive is not.

Complete packs and core packs differ in what they include. A complete pack usually names the drive in the box; a core pack usually leaves the drive out so you can keep an existing drive or choose one separately. Compare how this works in the complete pack guide and the core pack guide.

If a listing does not state the drive type or whether a drive is included, treat that as a missing detail and ask the seller before ordering. The drive is the one part that must match your steering.

Questions to ask before buying

Before you choose a drive, ask these questions:

• What steering type is on the boat (hydraulic, cable, chain or belt)?
• Does the pack include the drive, or is it a core pack without one?
• What does the maker's page say the drive connects to?
• Which model line does the listing belong to (for example Raymarine Evolution or Furuno NavPilot)?
• Will a dealer or a qualified installer fit the drive, per the maker's manual?

What to pick for your situation

Questions

What is a hydraulic autopilot drive?

A hydraulic autopilot drive is a pump that moves fluid in a boat's hydraulic steering system. It connects to the steering hoses and pressurizes one side or the other to turn the wheel or rudder. Raymarine names these pumps Type 0.5, Type 1, Type 2 and Type 3.

What is a rotary autopilot drive?

A rotary autopilot drive is an electric drive with a rotating output that turns a mechanical steering system, such as a chain, belt or gear. Raymarine offers Type 1 and Type 2 rotary drives for mechanical steering, which is common on sailboats with wheel steering.

Which do I need (rotary or hydraulic)?

Your boat's steering type decides. If the boat steers hydraulically, choose a hydraulic pump drive. If it steers mechanically with cables, a chain or a belt, choose a rotary or linear drive. The maker's page for each model states which steering system the drive connects to.

Can I keep my existing drive?

Yes, if you buy a core pack. Core packs include the electronics but leave the drive out, so you can keep a drive that already matches your steering. A complete pack, in contrast, includes the drive in the box.

Does an autopilot replace a lookout?

No. An autopilot is a steering aid, not a lookout. The U.S. Coast Guard's Boating Safety division emphasizes boating safety education and responsible operation, and the boat operator always keeps watch and remains in control.

Where do I find which drive fits my boat?

The maker's page for each drive or pack states what steering system it is made for. If you are unsure about your boat's steering type, Raymarine suggests consulting an authorized dealer or contacting the maker. A dealer or qualified installer can also confirm the fit.