The Scanmar Monitor Windvane

Gear Review · Self-Steering

The Scanmar Monitor is the most widely installed offshore windvane in the world. You will find them on the transoms of boats circling the globe, crossing the Atlantic in the ARC, competing in offshore rallies, and quietly steering across the Pacific while their owners sleep. The Monitor's market dominance is partly the result of a long production history — the design has been refined over 25 years — and partly the result of an approach to construction that makes field repair genuinely possible. Parts are available through a network of chandleries worldwide; the modular design means a bent servo blade or a worn bushing is a repair, not a replacement.

The Pendulum Servo Design

The Monitor is a pendulum servo system. It mounts on the transom and hangs a servo blade — a flat paddle — into the water. When the wind vane at the top of the unit detects a course deviation (the apparent wind angle has changed because the boat wandered), it rotates, and that rotation twists the servo blade sideways in the water. Water flowing past a blade angled to the flow generates an enormous side force, swinging the blade like a pendulum to one side. Lines run from the blade forward through turning blocks to the boat's wheel or tiller. As the servo pendulums over, it pulls these lines, moving the wheel and correcting course.

The physics are important: the correction force the Monitor applies to the rudder is far greater than the wind vane alone could generate. The water amplifies the input. In 20 knots of boat speed — a fast reach — the servo generates correction forces that significantly exceed what a human helmsman applies. This is why experienced offshore sailors rate pendulum servo systems as highly authoritative steering gear in heavy conditions.

Installation: Transom Mounting and Line Routing

The Monitor mounts to the transom via a bracket system that Scanmar has developed hardware for across a wide range of transom shapes. Flat transoms are straightforward — the standard brackets handle most configurations. Angled, curved, or complex transoms require the specific hardware kit for that geometry; Scanmar's customer service is notably helpful in specifying the correct kit from transom photos and measurements.

The sugar-scoop transom is the most common installation challenge. The Monitor needs clear water below the transom for its servo blade to swing freely, and a sugar-scoop that extends below the waterline limits that space. Some sugar-scoop installations require an extended bracket arm to push the unit further aft; others require relocating the attachment points higher on the transom. It is worth resolving this before purchase — mounting the Monitor well is important to its performance, and a poorly mounted unit is frustrating to tune.

Line routing runs from the servo blade's connection points forward through turning blocks to the wheel pedestal or to a tiller arm. On a wheel-steered boat, the lines typically wrap around the wheel's drum or attach to a dedicated drum fitted to the pedestal. Getting the block geometry right — minimum friction, correct lead angles — takes time during installation and pays dividends in responsiveness. Scanmar provides detailed routing guides; following them carefully is worthwhile.

Adjusting and Tuning the Monitor

Setting the Monitor to steer well requires understanding its two primary adjustments. The first is the wind vane angle setting: before you engage the gear, you set the vane to align with the current apparent wind angle. The unit then tries to maintain that angle. Getting the course right means setting the vane when the boat is already on the desired heading and the sails are trimmed — the Monitor remembers wind angle, not compass course.

The second adjustment is servo sensitivity, which controls how aggressively the system responds to wind angle deviations. A higher sensitivity setting means smaller deviations trigger a correction; lower sensitivity lets small deviations slide and corrects only larger excursions. In light conditions with gentle seas, higher sensitivity produces a tidier course. In heavy following seas where the boat is being pushed around by swells, dialing down sensitivity prevents constant over-correction that produces a weaving, uncomfortable motion. Finding the right sensitivity for conditions is the core of the Monitor's learning curve.

On different points of sail — upwind, reaching, running — the optimal settings change. Beating to windward in 20 knots requires a different sensitivity than broad-reaching in 15. Most experienced Monitor owners describe a two- to three-day learning period at the start of a long passage before the settings feel intuitive for the conditions at hand.

Offshore Performance

In the conditions the Monitor is designed for — 10 to 50 knots of wind, passages of days or weeks — it performs reliably. Once tuned properly, the unit holds a course to within a few degrees, self-correcting within seconds of a deviation. The corrections are smooth in moderate conditions; in heavy seas the pendulum swings more aggressively but the net effect remains a boat tracking well without human input.

Sailors who have crossed the Atlantic, Pacific, and Indian Oceans on Monitor-equipped boats consistently report that the gear needs little attention once set — check it once per watch, adjust the vane angle if conditions change significantly, and that is generally the sum of the interaction. This is the real value of the windvane on a long passage: crew energy is preserved because steering happens automatically.

The one condition where the Monitor's performance tends to be tested is the heavy following sea — storm-force conditions running downwind with large breaking waves pushing the stern around. A powerful sea can overwhelm the servo's corrective authority momentarily. This is not unique to the Monitor; all pendulum servo systems face this in extreme conditions. Most offshore sailors hand-steer through the worst of a storm regardless of what gear is fitted.

Annual Maintenance

The Monitor requires annual disassembly and inspection to stay reliable. The key items are the bearings and bushings throughout the pivot points, the servo blade itself (check for impact damage, cracks, or deformation), all fasteners (retorque after a passage, particularly the first offshore passage on a new installation), and the lines (inspect for chafe at every block and turning point).

Scanmar sells a complete bearing and bushing replacement kit. Replacing the wear parts on a schedule rather than waiting for failure is the standard practice among offshore sailors — a worn bearing that fails mid-passage is a more difficult problem than replacing one at the dock. The disassembly and reassembly process also gives you thorough familiarity with the unit, which is useful if you need to repair it at sea.

Monitor vs. Hydrovane

The Monitor and the Hydrovane are the two most common choices on offshore boats and serve different priorities. The Monitor's pendulum servo generates more powerful corrections in the full range of offshore conditions, particularly in the heavy following seas that test steering gear hardest. It is the choice of sailors who prioritize raw steering authority and who have confidence in their main steering system.

The Hydrovane, with its independent auxiliary rudder, provides true backup steering — if the main steering system fails, the Hydrovane continues to work. The Monitor, because it drives the main rudder, stops working if the steering system fails. Sailors making passages where gear failure could be life-threatening — solo, shorthanded, or simply cautious — often choose the Hydrovane specifically for this reason.

Buying a Used Monitor

A used Monitor can be an excellent purchase — the unit is built to last decades and parts are available. The inspection checklist matters, though. Check the servo blade carefully for bends, cracks, or impact deformation; a bent blade affects tracking and cannot be bent back effectively. Work all the pivot points by hand — they should move freely with no grinding or binding; stiff or gritty pivots indicate worn bearings. Check the wind vane for damage. Verify that all the hardware is present and matches a single generation of Monitor design; mixed-generation parts can complicate maintenance.

Ask the seller which generation the unit is. Scanmar has made design revisions over the years and can advise on parts compatibility for any serial number. Buying a used Monitor from a known generation with documented maintenance history is preferable to buying one with unknown hours. With a good inspection and a fresh bearing kit, a well-used Monitor can give another decade or more of reliable service.

← All Windvane Guides  |  Hydrovane Guide →

Frequently Asked Questions

How does the Monitor's pendulum servo system generate steering force? The Monitor hangs a servo blade — a flat paddle — into the water from the transom. When the wind vane detects a course deviation (the apparent wind angle has changed), it rotates and twists the servo blade sideways in the water. Water flowing past a blade angled to the flow generates an enormous side force, swinging the blade like a pendulum to one side. Lines run from the blade forward through turning blocks to the boat's wheel or tiller; as the servo pendulums over, it pulls these lines to correct course. In 20 knots of boatspeed, the servo generates correction forces that significantly exceed what a human helmsman applies — water amplifies the input.

What are the Monitor's two primary adjustments and how does each affect steering? The first adjustment is the wind vane angle setting — before engaging the gear, you set the vane to align with the current apparent wind angle while already on the desired heading with sails trimmed. The Monitor maintains wind angle, not compass course. The second is servo sensitivity, controlling how aggressively the system responds to wind angle deviations. Higher sensitivity corrects smaller deviations; lower sensitivity ignores small wandering and corrects only larger excursions. In heavy following seas, dialing down sensitivity prevents constant over-correction that produces a weaving motion. Finding the right sensitivity for conditions is the core of the Monitor's learning curve — most experienced owners describe a two- to three-day learning period at the start of a long passage.

What installation challenge does a sugar-scoop transom create and how is it resolved? The Monitor needs clear water below the transom for its servo blade to swing freely — a sugar-scoop that extends below the waterline limits that clearance. Some sugar-scoop installations require an extended bracket arm to push the unit further aft; others require relocating attachment points higher on the transom. Resolving this before purchase matters because mounting the Monitor well is critical to performance, and a poorly mounted unit is frustrating to tune. Scanmar's customer service is notably helpful in specifying the correct hardware kit from transom photos and measurements.

How does the Monitor compare to the Hydrovane and which situation favors each? The Monitor's pendulum servo generates more powerful corrections in heavy following seas and is the choice for sailors who prioritize raw steering authority and have confidence in their main steering system. The Hydrovane, with its independent auxiliary rudder, provides true backup steering — if the main steering system fails, the Hydrovane continues to work. The Monitor stops working if the steering system fails because it drives the main rudder. Sailors making passages where gear failure could be life-threatening — solo, shorthanded, or simply cautious — often choose the Hydrovane specifically for this backup rudder capability.

What does annual Monitor maintenance involve and why do experienced owners replace wear parts on a schedule? Annual maintenance involves disassembling and inspecting the bearings and bushings throughout the pivot points, the servo blade (checking for impact damage, cracks, or deformation), all fasteners (retorquing after a passage), and the lines (inspecting for chafe at every block and turning point). Scanmar sells a complete bearing and bushing replacement kit. Replacing wear parts on a schedule rather than waiting for failure is the standard offshore practice — a worn bearing that fails mid-passage is a significantly harder problem than replacing one at the dock. The disassembly and reassembly process also builds the familiarity needed to repair the unit at sea.

What should buyers inspect when purchasing a used Monitor windvane? Check the servo blade carefully for bends, cracks, or impact deformation — a bent blade affects tracking and cannot be bent back effectively. Work all pivot points by hand — they should move freely with no grinding or binding; stiff or gritty pivots indicate worn bearings. Verify that all hardware is present and matches a single generation of Monitor design, since mixed-generation parts can complicate maintenance. Ask the seller which generation the unit is and contact Scanmar with the serial number for parts compatibility advice. A well-used Monitor with documented maintenance history and a fresh bearing kit can give another decade or more of reliable service.