Auxiliary Rudder/Trimtab Self Steering Gear

For the skipper who wants the security of an emergency rudder and hates lines in the cockpit.

The horizontal axis airvane of the auto-helm windvane powers the trimtab. Water flowing past the trimtab controls the auxiliary rudder which, in turn, steers the boat. The boat’s main rudder is locked and used to balance the boat.

The auto-helm windvane is suitable for many boats under 50 feet. It is especially suited for boats with:



The auto-helm windvane became part of Scanmar windvane family in 1988. A proven self-steering gear for more than a decade it has since been improved and refined. It earns its excellent reputation from countless ocean crossings and circumnavigations. Today’s auto-helm windvane is thoroughly tested and perfected.

Superior Auxiliary Rudder Principle

The airvane develops information for course corrections. Because of the limited power of the airvane, the signal has to be amplified. Rather than connecting the airvane directly to the auxiliary rudder, the airvane controls the trimtab. Even though it is small, it has ample power to turn the auxiliary rudder.

Emergency Rudder

The auto-helm is a true emergency rudder which will effectively steer your boat back to port in case of main rudder failure. The semi-balanced auto-helm rudder is strong and efficient with a low drag, high lift profile.

No Lines in the Cockpit

The auto-helm windvane is not connected to the boat’s wheel or tiller. It is completely independent of the boat’s steering system leaving the cockpit uncluttered.

Superior Light Wind Performance

This self-contained windvane provides outstanding light air performance. It avoids the friction of the boat’s own steering system and much larger rudder area. As long as the boat is moving through the water, the auto-helm will literally "ghost" the boat along in light winds.

Directional and Downwind Stability

The directional stability of the boat, especially in heavy downwind conditions, is significantly improved because of the aft location of the auto-helm rudder. The extra rudder has a stabilizing and tracking effect of the boat.

Adjustable Airvane

The horizontal axis airvane is most powerful in the the vertical position. By pulling the airvane down towards the horizontal position, it can be easily reefed to control the power of the trimtab. When clearance for the mizzen boom is needed, the airvane can be pulled all the way down.

Autopilot Control

A small, inexpensive, electronic tiller-pilot can be rigged up to the counterweight of the auto-helm windvane. Instead of the airvane moving the trimtab, the electric autopilot will move it with minimum power consumption. To minimize interference the airvane is reefed to a horizontal position. This is an excellent set up for motoring or when sailing a close compass course.

Versatile Installation

The auto-helm comes in two halves - the airvane (upper) unit and the rudder (lower) unit. The two units can be totally separated, with the only connection being a wire running through a friction free teflon tube. The rudder can be mounted at the ideal height and the airvane higher up, where it gets the best wind. It is possible to avoid interference of davits, radar mast and other obstructions. The auto-helm windvane’s customized attachment system makes installation easy on most boats. Installation plans for hundreds of cruising boats are on file. Send us as much information as possible about your boat. We will make an installation drawing and mounting recommendation at no charge or obligation.


All rudder support parts in the lower rudder unit are made of stainless steel. The rudder and trimtab are hand laid, fiberglass laminates filled with closed cell, high density, polyurethane foam. The upper airvane unit is made of hard anodized 6061-T6, marine grade aluminum.


Upper airvane unit weighs 17 lbs (8 kg). Mounting hardware to the rudder is about 15 lbs (7 kg). True installed weight is only 32 lbs (14.5 kg) due to the reserve buoyance of the rudder.

Auto-Helm Upper Unit Only

A simple alternative for boats with outboard rudders The upper half is available separately to drive a custom trimtab on a boat with an outboard rudder. The trimtab is not provided by Scanmar International because size and design change from boat to boat. Some experimentation will be required. This is a simple and economical system for the sailor who is handy and does not mind making part of his windvane himself rather than buying a finished product.

Price List

Download the Auto-helm Manual as a PDF file


Totally Independent of Electricity

Manufactured and sold factory direct by Scanmar International.