I'm in the process of installing a Wheel Pilot Raymarine Evolution Autopilot into our 1998 Catalina 36 MkII (Hull #1712) to replace the original Raymarine ST4000+.  The new system includes an ACU-100, an EV-1 sensor core, a p70s controller, and the Evolution Wheel Pilot.  In preparation I’ve read numerous installation discussions here and elsewhere, viewed YouTube videos, and crunched numbers about wire sizes based on the layout of our specific boat.  While these discussions and videos have been very helpful regarding installation and possible locations of these components as well as issues with the SeatalkNG network, based on available information regarding the wiring I have come to a conclusion.  The 16 AWG drive cable included in the package for the Wheel Pilot motor appears to violate the ABYC requirements for maintaining a maximum voltage drop of 3%.  This cable also appears to violate the tables in the Evolution EV-1 & ACU installation manuals in that there are no lengths listed in the examples that use 16 AWG cable, not to mention that the wire requirements in the 2017 (Rev-4, P36)) and 2024 (Rev-7, P64) manuals do not agree.  Specifically, Rev-4 appears to have one-way lengths while Rev-7 appears to have total lengths while neither is clear about the basis for these requirements.  At a “Grand and a half” I would hope that the authors of these manuals would have some more of an idea than a bunny rabbit about these important issues but this does not seem to be the case!  But yes, there is a question on the horizon which I will get to shortly.

The specifics of the install are as follows.  The boat originally came with Autohelm ST50+ Wind, Speed, and Depth as well as an ST4000+ Autopilot in a single Navpod mounted to rails above the Edison Helm.  When we purchased the boat in 2012 we added a Garmin 441S chart plotter which was powered from the wiring at the helm; I don’t recall the wire size.  In 2023 the three ST50+ gauges were replaced by two i50’s (speed & depth) and an i60 (wind).  The installation was done by the marina that was doing other tasks (new life lines & standing rigging, etc.) and they reported intermittent power at the helm and so ran a new wire (14 AWG)  to the helm.  Given the location of the electrical panel on the starboard side of the Cat 36, the 14-2 wire runs thru the hanging locker in the aft cabin, behind the starboard bulkhead, through the transom, into the central roof of the aft cabin up to the helm, a distance of 24-25 feet (round trip of 48-50 ft).  For the low current requirements of the i50, i60, and 441s this is adequate (deltaV~3%) but not for the autopilot.  The ST4000+ failed shortly after though the circumstances around its failure are not clear.

The current autopilot setup is as follows.  The SeatalkNG network is powered at the helm.  This includes the p70s, the 2 i50’s, the i60, and the 441s chart plotter at the helm.  The ACU-100 (STNG only) and EV-1 located inside the aft cabin are also powered by the STNG network.  The ACU-100 is located inside the hanging locker in the aft cabin and the EV-1 is mounted on the aft-facing side of that locker with both units connected to the STNG network inside the locker.  The critical issue is the wiring from the panel to the ACU and from the ACU to the wheel drive motor.  At present a 4 ft length of 12-3 AWG wire brings power to the ACU, a 15.5 ft 10-2 AWG wire brings motor power to the bottom of the helm which is butt-connected to 5 ft of the supplied 16-2 AWG wheel drive cable, a round trip of 49 ft.   Initial tests show the wheel drive motor works but the voltage drop calculates to be about 7%.  So here’s my question; is this good enough or do I need to improve the wire quality between the panel and ACU and/or upgrade the stock 16-2 wire supplied by Raymarine?  An interesting point is that the 5 ft of 16 AWG produce about twice the voltage drop (0.45V) compared to the 15.5 ft of 10 AWG (0.23V).  Sorry for such a long winded description but most people talk at length about where to mount this stuff (which is important) but very rarely mention wiring issues (size &/or length) which is extremely important and difficult and expensive to change once put in place.
Thx in advance
J Morrill
Enterprise
Catalina 36 Mk II
Hull 1712