Autopilot for Multihulls: Rudder and Torque Needs

What a Multihull Changes in Autopilot Choice

A catamaran or trimaran autopilot is chosen by the same two details as any other boat: the steering already aboard and the drive that can move the rudders. The hull shape changes how the rudders load up, so the drive's torque and response get the attention, but the buying question stays the same. Match the drive to the steering type and to the boat's size and weight as the maker states it.

Multihulls are wide, light for their sail area, and stay level when the wind builds. Their rudders see a different load pattern than a deep-keel monohull. General boating knowledge says a wide, light hull answers the rudder quickly, and the rudders carry significant water load at speed. The autopilot needs a drive that can supply enough torque to move the rudders and respond fast enough to avoid constant correcting. That is why listings name the drive type and why this site compares stated details only. Start with the main marine autopilot guide.

Rudder Response: How the Boat Answers

Rudder response is how quickly the rudder moves and how directly the hull answers. On a multihull with twin rudders or large balanced rudders, the boat can answer with little delay, and the autopilot has to keep up. If the drive moves the rudder slowly, the boat may wander between corrections at speed. This is why the catalogue names rudder speed and drive speed as details to compare; see rudder speed specs.

The maker's software can adapt. Furuno states that its NavPilot uses a self-learning algorithm and adjusts for vessel speed, trim, draft, tide and wind effects. Raymarine describes its Evolution autopilots as self-calibrating. Those are the makers' own descriptions; they tell a buyer that the autopilot is meant to learn how a particular hull steers rather than assume a fixed response. Compare that with your boat's torque requirement.

Torque and the Drive Unit

Torque is the turning effort applied to the rudder or steering system. Most listings do not give torque numbers; they name the drive type instead: linear drive, rotary drive, or hydraulic pump. For a multihull with heavy rudder loads, the drive's capability matters more than the control head. The drive types article explains the difference.

The maker's page is where a buyer reads limits. Raymarine states its cockpit tiller drive is for tiller-steered sailing boats up to 6,000 kg (13,000 lbs) displacement, and its Type 1 rotary drive for vessels up to 11,000 kg (24,000 lbs). A multihull owner compares the boat's displacement and steering to those stated ranges. If the steering type is not certain, Raymarine advises consulting an authorized dealer. See the hydraulic autopilots guide.

• Compare the drive type in the box, not just the model line.
• Check whether a control head is included in the pack.
• Read the maker's displacement range before ordering.

Sail Multihull or Power Multihull

A cruising sail multihull usually has wheel steering, and the pack name often says 'sail pilot'. Raymarine's packs page lists an EV-200 Sail Pilot for mid-sized sailboats with mechanical steering and an EV-400 Sail Pilot for large sailboats with mechanical steering. A small trimaran with a tiller may use a tiller pilot; the sailboat autopilot guide covers the choices.

A power multihull commonly has hydraulic steering, and a hydraulic pump drive is the usual choice; see the powerboat autopilot guide. A boat with an electronic helm uses a steer-by-wire pack that has no drive in the box; see the steer-by-wire guide. A fishing multihull with a kicker motor may add a kicker autopilot; the kicker motor guide covers that case.

What to Read on a Multihull Autopilot Listing

The title names the model line and pack contents. 'Core pack' means no drive in the box; 'complete pack' includes a drive and often a control head. 'No drive', 'no pump' and 'requires pump' all tell you the drive is separate. Read those words before comparing pack sizes.

The bullet list states the steering type and the drive version. Compare two listings on stated details only: what the drive is, whether a control head is included, and what the maker's page says about displacement. Missing details are a sign to open the maker's page or ask the dealer. The complete packs guide and the core packs guide show how these words sort the choices.

Sensors and Network

An autopilot needs a heading source. Furuno states that its NavPilot 300 requires a Furuno PG700, SC33, SCX20 or another compatible NMEA 2000 heading source. That tells a buyer that some packs leave the sensor out, and the sensor becomes a separate question.

NMEA 2000 is the network standard an autopilot uses to share heading and waypoint data with a chartplotter and other instruments. The NMEA describes it as a bi-directional, multi-transmitter instrument network with no central controller. See the NMEA 2000 article for what to compare.

An Autopilot Does Not Replace a Lookout

An autopilot steers while the operator watches. The U.S. Coast Guard's Boating Safety Division works to reduce loss of life, injuries and property damage on U.S. waterways, and keeping watch is part of the operator's duty. This site makes no safety claims and no claim that an autopilot keeps a boat safer; it only compares stated details.

What to pick for your situation

Questions

Do multihulls need a different autopilot from monohulls?

No separate product line for multihulls is listed on the maker pages cited here. The buying rule is the same as for any boat: match the drive to the steering type and to the boat's displacement as the maker states it. Multihull rudder loads are a reason to read the displacement range carefully, not a reason to buy a special brand.

What does torque mean on an autopilot listing?

Torque is the turning effort the drive applies to the rudder or steering system. Most listings do not give a torque number; they name the drive type, such as linear drive, rotary drive, or hydraulic pump. The maker's page gives displacement ranges that help you compare.

What is a core pack and why would I choose one for a multihull?

A core pack leaves the drive out. A multihull owner who already has a suitable drive, or who wants a dealer to match the drive to the rudder load, can buy the core pack and add a drive separately.

What is a rudder reference?

A rudder reference, also called rudder feedback, tells the autopilot the rudder's position. Furuno notes that its NavPilot 300 does not require a physical rudder feedback unit for outboard installations, while other modes require a Rudder Reference Unit. Whether a pack includes one is a stated detail to compare.

Should I keep my existing drive when adding an autopilot to a multihull?

If the drive matches the steering and the maker's displacement range, keeping it is a valid choice and a core pack fits that plan. A dealer should confirm the drive is compatible with the autopilot line being added.