Self Steering

(Posted 10/28/2016)

Our DIY self steering system is based on the rudder head mount (RHM) pendulum self steering system developed by Jan Alkema. If it works, it will save us countless hours of hand steering.

Part of our desire to build the self steering system stemmed from my preference for an outboard rudder (transom hung), as they are easier to fix if a problem develops. Minimus has an inboard rudder, so the addition of an outboard auxiliary rudder was appealing. Under sail, our plan is to adjust the sails and main rudder so Minimus is balanced, then lash the tiller. At that point, relatively little stress will be on the self steering system, which will enhance its ability to steer the boat.

If the system doesn't work, I suspect it will be because the axis of rotation of the pendulum oar is not parallel to the axis of rotation of the auxiliary rudder. Jan Alkema's boat had a vertical transom, so the two axis were parallel. Minimus has an angled transom, which causes a difference of about 30 degrees between the two axis. This difference introduces a slight rearward vector of motion in the oar and oar carrier as the oar swings out. If the restraint lines are tight, as they ideally should be, the oar carrier consequently binds when the oar swings out. So, the restraint line will have to be left slightly loose, which will cause a bit of hesitation before the lines come tight and the oar causes the auxiliary rudder to correct. How this will work in practice remains to be seen.

As with many other aspects of our trip, we hope to be posting updates here as we gain experience with the system.

Rudder head mounted self steering system, showing wind vane, auxiliary rudder, pendulum oar carrier, pendulum oar and restraint line.	When boat gets off course, wind vane cants over, causing pendulum oar to swing out, forcing auxiliary rudder to opposite side, thus steering boat back on course.
Showing wind vane canted to one side, pendulum swung out and auxiliary rudder forced to opposite side.	Another angle showing pendulum oar swung to one side, forcing auxiliary rudder to opposite side.
Wind vane assembly	Side view of wind vane assembly.
Close up of wind vane assembly. Donut-shaped disk is rotated to face vane in line with wind, then red clamp holds it in place. When boat gets off course, vane cants over, thus moving cords through pulleys which cause pendulum to swing to one side, in turn causing auxiliary rudder to swing to opposite side, steering boat back on course.	Top view of RHM self steering system, showing cords through pulleys that transmit motion of wind vane to pendulum oar.