Boat Project: Autopilot

Stepping away from our (way behind) trip stories to talk about a recently completed boat project. This one has been in the works for a while now, but we finally got it finished while in Tadoussac, and testing over the following days was successful. The project was installing a second (backup) autopilot drive system on our boat.

Sailboat autopilots get a lot of use when you’re cruising. On an offshore passage, your autopilot (or windvane steering if you have it) is more than a convenience, it’s safety critical. Steering the boat by hand for hours or even days on end is really tiring, especially with a shorthanded crew. More than a few of the accident stories you can read about follow a similar plot… “the autopilot failed and we had to hand steer for days, and then X (really bad thing) happened”.

We use our autopilot every day when we’re sailing. In fact “Will” (our name for the autopilot, short for “Willhelm”) does most of the driving on Innisfree. Sailboat autopilots have many features, but basically they allow you to set the boat to steer a fixed compass direction, or at a fixed angle to the wind. The first is pretty easy to understand. The second is very handy when sailing… by keeping the angle to the wind consistent, the sails don’t need to be adjusted. Often the wind direction will oscillate 10 degrees or more, and it’s nice to have the autopilot adjust course a bit to keep the boat moving as fast as possible. If a big wind shift happens, you can of course change the sails and settings to make sure you don’t go the wrong way!

The autopilot system has really three active components and a collection of sensors that provide data. There’s a controller (a “brain”), a control panel for the crew to adjust the settings, and a drive unit that is connected to the rudder to control the boat. The sensors provide data including compass direction, wind direction, rudder angle, etc.

On a moving boat, it wouldn’t be too difficult to replace the controller if it failed, so we can carry a spare. If needed, we can also control the autopilot settings from other devices on the boat, so that’s a backup option to the control panel. The drive unit is trickier. Connected to the rudder in a difficult to access crawl space, replacing the drive unit on the fly (while the rudder is moving about) would be difficult and maybe even dangerous. As a result I decided early on that not only should we have a spare, but we should figure out how to rig that spare drive unit in such a way that we switch to it on the fly.

I bought a 1012LAR7 hydraulic linear drive unit made by Octopus Drives in British Columbia in 2021 while we were refitting the boat. These small, powerful systems have a good reputation for reliability and their design provides flexibility on where one can locate the hydraulic pump that powers it – something that was important considering space constraints I was dealing with. The Octopus unit sat in storage on the boat last summer and I didn’t really get started on this until February of 2022; other upgrades and boat projects took priority.

The project involved a few challenges:

  1. building a mount into the hull where the drive unit would connect,
  2. attaching the drive unit to the rudder post, and
  3. mounting the hydraulic pump and wiring up the system


The mount was what I started in February, and the big obstacle was geometry. Once installed, the drive unit pushes on a short arm (called a “tiller arm”) that is clamped onto the rudder post. The drive unit has to be oriented so that when the rudder is straight, the drive and tiller arm make a 90 degree angle. If you imagine the tiller arm sweeping across a flat plane as the rudder rotates, the drive unit has to be mounted in that same plane (so it’s not pushing up or down on the tiller arm, only side to side). It doesn’t sound too complicated until you realize that the rudder post on our boat isn’t vertical, it’s leaned at an angle towards the stern, which means that the plane of the tiller arm is inclined at that same angle. And the mount for the drive unit (that I would have to build) isn’t built on a nice flat surface, but on the complex rounded shape of the hull. Lastly, because of space constraints, I couldn’t mount the drive unit angled directly across the boat – I had to rotate the drive and the tiller arm to one side. And Octopus generously allows for the mount to be misaligned by a whole 5 degrees (eyeroll).

I first built a cardboard jig to get a feel for the space and where things might go, then created a more rigid plywood jig with the exact geometry of the tiller arm and drive unit, and its mounting holes. This allowed me to build a cardboard template for the mount where it would fit on the hull – a shape a bit like a box cut in half at a weird angle. Tripled checked for dimensions, I then built a plywood version of that box mount and used fiberglass to strengthen it. This mount had to be STRONG, because the drive unit can push and pull with up to 900 pounds of force as it fights to move the rudder back and forth.

After fit checking again, I sanded away the hull paint to the bare fiberglass and bonded the mount to the hull, again building up multiple layers of fiberglass and epoxy inside and out to add strength and spread the load across a wider area of the hull. I then drilled holes for the drive unit bolts and painted it all to make it look a little nicer.

Tiller arm

Attaching the tiller arm to the rudder post was also tricky. As mentioned above, the space constraints meant that I had to rotate the system to one side to fit it in. Our rudder post (a 1.5″ diameter cylinder of stainless steel) is keyed: there is a slot cut on the aft side that allows the steering components to “lock” on to the rudder post to they don’t slip. I could have purchased a keyed tiller arm, but the keyway on our rudder post doesn’t extend down all the way into the area where I was going to mount the tiller arm, nor did I know exactly the angle on which I’d be mounting it. Instead I purchased a Jefa Tiller Lever (arm) with locking bolts. The locking bolts are machine screws with cones on the end – once I had the arm oriented where it would go, I needed to drill into the rudder post a bit to create a dimple where the locking bolts would push into and prevent the tiller arm from rotating around the rudder post.

My exercise in templating the whole system above also fixed the location of the tiller arm. With some gracious assistance from the machinists at work, we drilled a new mounting hole for the drive system the right distance from the rudder, trimmed the tiller arm to size (it was longer than it needed to be), and used the lathe to drill a hole down the center of a spare machine screw the same size as the locking bolts. Using this machine screw as a guide, I could mount the tiller arm, put this modified machine screw into the holes for each locking bolt, and then drill through the middle and keep it all straight. Drilling in stainless is hard enough. Drilling backwards (drill pointing towards me) into a curved stainless surface and expecting good results would have been nearly impossible without this little jig. Thank you Paul and Craig! While some sweating was involved, in the end it all went pretty seamlessly.

Pump and wiring

Mounting the hydraulic pump and wiring it in was more straightforward. I built a shelf near the rudder for the pump and ordered two DPDT switches for swapping between autopilot drives. The autopilot drive units have four wires that control them. One pair of wires is for a clutch that engages or disengages the drive unit from the rudder (so you can turn the steering wheel by hand and not fight against the autopilot). The other pair of wires are for power to drive the rudder back and forth. I installed one switch each for the clutch and power, respectively. In principle, a single 4PDT switch would have been ideal, but they are pretty rare beasts.

Tiller arm secured to rudder shaft with Octopus Drive unit connected

Now, if our primary drive unit (the original Raymarine Type 1 Mechanical Linear Drive) has a problem, we can turn off the power to the autopilot, switch the two switches to the Octopus Drive, power the system up again and do a quick calibration, and off we go.

Finally fully installed, we tested the Octopus Drive unit for nearly 24 hours of sailing after leaving Tadoussac and it worked well. Success!

Now, as long as all the other boat projects don’t take me a year and a half to finish…