Rotary vs Linear Drive: Which Autopilot?

What rotary and linear drives do

An autopilot drive is the part that moves the boat's steering. The two common electric drive types are rotary and linear. A rotary drive spins a wheel or a steering shaft. A linear drive extends and retracts a rod to push or pull a tiller arm or a rudder linkage. Both do the same job in general terms: they move the steering so the boat follows the course the autopilot sets. For a broader view of how autopilots fit into a boat's systems, you can read the best marine autopilot guide.

The drive is one of the parts a listing names. When you read a title like "Type 1 Rotary Drive" or "Type 1 Linear Drive Unit," the words rotary or linear tell you how the drive moves the steering. The maker's page for the drive unit states which steering systems it suits. For example, Raymarine lists a Type 1 Rotary Drive for vessels up to a certain displacement and a Type 1 Linear Drive Unit for boats up to the same displacement, but each interfaces with a different steering setup.

Your boat's steering decides which drive type you need. A wheel-steered boat may accept a rotary drive mounted on the wheel column. A tiller-steered sailboat needs a linear drive that can push the tiller. A boat with hydraulic steering uses a hydraulic pump drive, not a rotary or linear unit. So the first question is not which drive is better, but which drive matches the steering already aboard.

• Rotary drive: turns a wheel or steering shaft.
• Linear drive: pushes or pulls a rod to move a tiller or rudder arm.
• Hydraulic pump: moves fluid to turn a hydraulic steering system.

Rotary drives for wheel steering

A rotary drive is a compact electric motor that mounts near the steering column and turns the wheel or the shaft. It suits boats with mechanical wheel steering, where a cable or chain connects the wheel to the rudder. The drive replaces the effort of your hands by rotating the wheel itself.

On a listing, a rotary drive may appear as a named unit, such as "Type 1 Rotary Drive" or "Type 2 Rotary Drive." The model name often includes a type number that the maker uses to match the drive to boat size. Raymarine's drive unit page lists Type 1 Rotary Drives for vessels up to a stated displacement and Type 2 Rotary Drives for larger vessels. The maker's page is the source for which boats a drive suits. If you are looking for a powerboat setup, the best powerboat autopilot guide can help you compare options.

Rotary drives are common on powerboats with wheel steering and on some sailboats with wheel steering. They are not used on tiller-steered boats, because a tiller moves side to side, not in a circle. If your boat has a wheel, a rotary drive may be the direct way to add autopilot control without changing the steering system.

Linear drives for tiller and rudder control

A linear drive is a motor that moves a rod in a straight line. It attaches to a tiller arm or a rudder linkage and pushes or pulls to steer. This makes it a natural fit for sailboats with tiller steering, where the autopilot can act directly on the tiller. For a list of tiller-specific autopilots, see the best tiller pilots guide.

Raymarine's drive unit page lists a "Cockpit Tiller Drive" for tiller-steered sailing boats up to a stated displacement, and a "Type 1 Linear Drive Unit" for boats up to a similar displacement. The tiller drive is a self-contained unit that mounts in the cockpit. The linear drive unit is a mechanical drive that connects to the steering linkage.

Linear drives also appear on powerboats with a rudder arm, such as some inboard or sterndrive boats. The drive pushes the rudder arm directly. On a listing, you may see "linear drive" in the title or in the bullet list. The maker's page states which steering systems the drive suits, so check that before comparing listings. The best sailboat autopilot guide covers many of these drive options for sailboats.

How to choose between rotary and linear

The choice between rotary and linear is not about which is better in general. It is about which drive fits your boat's steering. Start by identifying the steering type: wheel, tiller, hydraulic, or cable. Then look for a drive unit that the maker lists for that steering type.

For a wheel-steered boat, a rotary drive is often the listed option. For a tiller-steered sailboat, a linear or tiller drive is the listed option. For a boat with hydraulic steering, neither rotary nor linear applies; you need a hydraulic pump drive. The best hydraulic autopilot guide explains that category in detail. The maker's drive unit page is the authority on which drive matches which steering system.

When comparing listings, read the drive name and the maker's stated details. A listing that says "Type 1 Rotary Drive" is for a different steering setup than one that says "Type 1 Linear Drive Unit." Do not assume one is better because of the type number. The type number is a maker's sizing label, not a ranking.

If you are unsure which drive your boat needs, the maker's page and an authorized dealer are the sources to ask. The installation of any drive is a job for a qualified installer following the maker's manual. This article can only help you read listings, not tell you which drive fits your specific boat.

What listings tell you

A listing title often names the drive type. For example, "Type 1 Rotary Drive" or "Type 1 Linear Drive Unit" are clear signals. The bullet list may add details like the steering system it suits, such as "for wheel steering" or "for tiller steering." Read those words carefully.

Some listings are for complete autopilot packs that include a drive. Others are core packs that leave the drive out. If a pack includes a drive, the title or bullet list will name it. If the listing says "no drive" or "requires pump," then you need to buy a drive separately, and the drive type becomes your choice. The best complete autopilot packs guide shows what a full system includes, while the best autopilot core packs guide focuses on systems without a drive.

The catalogue on this site lists complete autopilots and packs only, and it compares them on stated details. That means the drive type, the control head, and the boat type are the facts you can compare. Performance claims, such as how well a drive holds course, are not part of the comparison. The maker's page is the source for what a drive is designed to do.

Common questions about drive types

Can a rotary drive work on a tiller boat? No, a tiller moves side to side, so a linear or tiller drive is the match. Can a linear drive work on a wheel? Not directly; a wheel turns in a circle, so a rotary drive is the usual match. These are general statements, and the maker's page decides fit for a specific boat.

What about hydraulic steering? Hydraulic steering uses a pump drive, not a rotary or linear unit. The pump moves fluid to turn the steering. Some listings name the pump type, such as "Type 1 Hydraulic Pump." That is a separate category from rotary and linear drives.

Do I need a rudder reference with a rotary or linear drive? Some autopilot systems use a rudder reference to know the rudder angle. The listing or the maker's page will state if a rudder reference is included or required. This is a detail to check before buying, not a general rule.

The best way to choose is to read the drive name on the listing, check the maker's page for the steering systems it suits, and ask a dealer if you are unsure. The drive type is one of the first facts a listing gives you, and it is the fact that decides whether the autopilot can connect to your boat's steering.

What to pick for your situation

Questions

What is the difference between a rotary and a linear autopilot drive?

A rotary drive turns a wheel or steering shaft. A linear drive pushes or pulls a rod to move a tiller or rudder arm. The drive type must match your boat's steering system.

Can I use a rotary drive on a tiller-steered sailboat?

No, a tiller moves side to side, so a linear or tiller drive is the match. Rotary drives suit wheel steering. See the best tiller pilots guide for sailboat options.

Do linear drives work on powerboats?

Yes, linear drives can work on powerboats with a rudder arm, such as some inboard or sterndrive boats. The maker's page states which steering systems the drive suits. The best powerboat autopilot guide can help you compare.

Is a rotary drive better than a linear drive?

Neither is better in general. The right drive depends on your boat's steering type. Compare listings on stated details, not on performance claims.

What if my boat has hydraulic steering?

Hydraulic steering uses a hydraulic pump drive, not a rotary or linear unit. Look for a listing with a pump drive, such as a Type 1 Hydraulic Pump. The best hydraulic autopilot guide covers this category.

Where can I find out which drive my boat needs?

Check the maker's drive unit page and ask an authorized dealer. The installation is a job for a qualified installer following the maker's manual.