Raymarine ACU-100 Autopilot

• Action: To Do List item A0261 – Install Raymarine Evolution ACU-100 Actuator Control Unit at outboard wall of navigation desk area.
• Action: To Do List item A0262 – Install Raymarine Tiller Drive connector at aft starboard cockpit wall and route power cable.
• Completed:  23 April 2018
• Cost: $769.36

The manuals for the Raymarine Evolution ACU-100 Actuator Control Unit (ACU) autopilot and Tiller Drive were downloaded from the Raymarine website and reviewed.  As a result of the review, added additional items to the To Do List.

Added to the To Do List:

• Item A0291 - Mount and install Raymarine Tiller Drive.
• Item A0292 - Perform Raymarine autopilot initial set-up and commissioning.

The pertinent information gleamed from the documentation was:

• Maximum motor power output - 7 Amps.
• Internal power fuse - 10 Amp ATC type.
• RF Ground connection - Run of < 3 feet use #10 AWG or greater.
• Tiller Drive Cable Size - 23–32.8 ft use 12 AWG.

Per the manual, the total wire length for voltage drop calculations needed to be from the power source to the tiller drive connector.  The length of wire from the circuit breaker panel to the ACU-100 was estimated to be 4-feet and from the ACU-100 to the tiller drive was estimated to be 11-feet, therefore the total estimated wire length was 15-feet. To determine the actual size of the wire needed we used the following formula (ref 46 CFR §183.340.(p) and ABYC E-9.14.e.(4)):

CM = (K x I x L)/E

 Where:
CM = Circular mil area of conductor.
K = 10.75 (constant representing the resistivity of copper).
I = Load current in amperes.
L = Length of conductor from the positive power source connection to the electrical device and back to the negative power source connection, measured in feet.
E = Maximum allowable voltage drop at load in volts (For a three percent voltage drop at 12V, E= 0.03 x 12 = 0.36).

We used the value of 10.75 for K, 7 amps current draw at 12 V for I, 30 feet (15ft x 2) for L, and 0.36 as the 3% voltage drop for E.

CM = (10.75 x 7 x 30)/0.36 = 6,270.8 which equates to 12 AWG which has a CM of 6,530; ref ABYC E-11 (7/15) Table XI.

The following picture illustrates the electrical installation diagram.

The following items were purchased to support this installation.

The location chosen to mount the Raymarine ACU-100 autopilot was at the navigation desk outboard wall. The starboard side of the hull at this location only had a thin 1/8-inch piece of plywood covering approximately 1/2-inch of insulating foam. A 1/2-inch piece of plywood was cut, epoxied, and attached to the starboard side of the hull to provide a solid mount surface.  The Raymarine SeaTalkng spur cable was attached first to the ACU-100 autopilot and the plug on the opposite end was connected to a SeaTalkng 5-way connector block located in the same area.  Routed 12/2 AWG duplex wire from the 12V DC circuit breaker panel 10 amp circuit breaker to the ACU-100 autopilot.  Installed a 10 AWG RF ground wire from the ACU-100 autopilot to a negative busbar located about a foot away.  Then routed 12/2 AWG duplex wire from the ACU-100 autopilot to the tiller drive connector mounted on the aft starboard cockpit sidewall.

It was discovered that on the ACU-100 autopilot label the maximum amperage was identified as 7.5A, see picture above circled in red.  The 7.5A rating was higher than the 7.0A rating listed in the manuals.  Rechecked the wire calculations with I = 7.5A instead of previous value of 7A.   CM = (10.75 x 7.5 x 30)/0.36 = 6,718.8 which now equates to 10 AWG which has a CM of 10,380 since 12AWG has a CM of 6,530 - just below the calculated CM value by 189 CM; ref ABYC E-11 (7/15) Table XI.  While the calculated CM value is now slightly larger than the 12 AWG rating, it was too late to upgrade to 10 AWG as the 12 AWG was already laid in.

The ACU-100 autopilot will be powered on as part of the software loading action of To Do List item A0271.