My Raymarine autopilot came equipped with a rudder position sensor which aids the course computer in steering a straight course. The problem with these sensors is that it is a servo type device that needs to monitor the rudder quadrant for it's position and must be installed so it can handle the swings of the rudder to a full stop on both the port and starboard turns.
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Rudder Position Sensor - Quadrant Close Up
In this picture you can see the rudder quadrant and the Starboard shim I made to attach the rudder position sensor arm to. Starboard is a high modulus engineered plastic sheet product available in thicknesses to 3/4 inch. Starboard is impervious to moisture and rot and is very well suited for use on a boat that is why I chose to use it. It works, cuts and taps similarly to wood and is a tremendously useful but expensive product.
On many Edson steering quadrants there are two 5/16 threaded holes already drilled and tapped into its surface. I simply measured the center to center of these 5/16 threaded holes and transferred the measurements to the Starboard shim using a set of calipers. I then drilled the two holes and mounted the ball (the arm has a socket and the base is a ball) to the Starboard perfectly centered between the two 5/16 holes. With the ball finally mounted, and screwed into the Starboard shim, I then bolted the shim to the quadrant. In the picture you can see the two 5/16 bolt heads with the ball mount for the sensor in between them.
Rudder Position Sensor Base
On my Catalina there is a fiberglass shelf, for the water heater, that is perfectly level and very close to the steering quadrant. This is good because I knew the sensor needed to be on the same plane as the quadrant and now all I needed to come up with was a mounting bracket. The bracket only needed to elevate the sensor, and make it level with the quadrant, but unfortunately you can't just buy a pre-made bracket that size. Fortunately, because of the water heater shelf, the bracket did not need to be of an odd angle defined by the hulls shape.
After considering many options I decided to make a bracket out of one inch stainless steel rail / dodger tubing and two 90 degree stainless steel deck fittings. I measured for the bracket height by laying a flat edge across the quadrant and measuring from the flat edge to the the water heater shelf. I then subtracted, one half inch of total height, for the Starboard base plate the sensor would eventually be bolted to.
To cut the one inch stainless steel pipe I used a Rigid pipe cutter commonly used for cutting copper pipe. The blade was not a stainless blade but it did work, and made a perfectly clean cut, in the one inch stainless steel.
Next I needed to attach the deck fittings to the pipe. The fittings come with set screws but I did not fully trust them in this situation. To be sure the deck fittings would not twist under a load I tightened the set screws then removed them leaving a mark on the tubing where I needed to drill two very small holes. I drilled the two holes and then re-installed the set screws. The set screws have a pointed tip and the hole was jut big enough to accept 75% of this tip so they would not allow the deck fittings to twist. I used Loctite on the set screws, when re-installing them, just to make sure they would not back themselves out.
Rudder Position Sensor Quadrant Mount
In this photo you can see the quadrant, shim, the ball & socket & the stainless steel threaded rod connecting the RPS (rudder position sensor) to the quadrant.
Rudder Position Sensor Top
This is the actual RPS and the Starboard base plate it's mounted to. It's critical to the performance of the Autopilot that the sensor be installed so it's mounted in-line with the center line of the hull and then bolted down in this position. I found it easiest to line up the base and top plates before installing the set screws so I had nice 90 degree angles to work off of. Once the RPS is installed you must then make sure the rudder does not over steer the device.
If the rudder can turn more than the RPS can handle it will break plain and simple. I had to adjust my rudder stops ever so slightly just to accommodate the RPS. Installing the threaded connector rod is simple but it will need to be cut to length and it took me two cuts to get it perfect. Never cut short and always err on the large side when test fitting this piece.
Once all the hardware is installed you simply run the RPS data wire to the Autopilot control head and connect it.
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