Overview

The Raymarine M81135 is a Type 1 rotary autopilot drive for 12V DC steering systems that use a chain and sprocket from the helm. It is built for mechanically steered powerboats and sailboats where the existing cable or rod steering can be driven through that chain-and-sprocket arrangement.

This drive suits vessels up to 11,000 kg or 24,000 lb displacement and works with the Raymarine ACU-200 actuator control unit. Its rotary mechanism uses an electric motor, epicyclic gearbox, drive belt, and electromagnetic clutch to turn the steering system under autopilot control while allowing normal hand steering when the clutch is disengaged.

For installation, the steering layout needs enough space near the chain run, and the correct sprockets, chain hardware, and mounting fasteners must be matched to the boat. In many installations, the steering chain may need modification so the drive can engage cleanly without adding unwanted friction at the helm.

Key features

• Type 1 rotary autopilot drive for chain-and-sprocket mechanical steering systems.
• 12V DC configuration for vessels with a 12-volt onboard power system.
• Rated for boats up to 11,000 kg or 24,000 lb displacement.
• Works with the Raymarine ACU-200 actuator control unit.
• Electric motor drives an epicyclic gearbox through a high tensile drive belt.
• Electromagnetic clutch lets the drive engage for autopilot steering and disengage for hand steering.
• Well suited to cable and rod steering systems that can be driven from the helm position.
• Optional drive sprockets and steering-chain changes may be required for a correct fit.

Installation and setup

The M81135 installs below deck or in another protected steering area where it can connect mechanically to the boat’s steering chain. The drive must be mounted securely so steering loads transfer through the drive and chain without flexing the mounting surface or pulling the sprockets out of alignment.

Before ordering, the steering system should be checked for displacement rating, 12V compatibility, available mounting space, and chain access. The sprocket size and chain path matter because they affect how the rotary drive turns the helm system and how freely the steering feels when the autopilot is not engaged.

Compatibility and fit

This unit is for mechanical steering systems that can be driven by a chain and sprocket. It is not a hydraulic pump, linear ram, or wheel-mounted cockpit pilot. Boats with hydraulic steering, stern drive steering, or a steering system that cannot be back-driven need a different Raymarine drive type matched to that steering arrangement.

It is a practical match for cruising sailboats and powerboats that already have a mechanical helm layout and need below-deck autopilot steering with enough authority for longer passages, coastal runs, and regular hands-off course keeping.

Electrical and system integration

The drive is powered and controlled through the autopilot system rather than wired directly to a display. In a typical Raymarine Evolution autopilot setup, the ACU-200 supplies drive control while the sensor core, control head, and compatible chartplotter or instruments handle heading data and user input.

Because this is a steering drive, cable routing, circuit protection, and mechanical installation should be planned together. A clean installation keeps the drive wiring protected from heat, moving steering parts, and moisture while leaving access for inspection and service.