Take a look at the ComNav 1101. I have installed them on a Hatteras 54 sportfisherman, a couple of
CSY 44's and am putting 1 in my 12 ton yawl (Rhodes Reliant). Most
head units which talk the
NMEA lingo can command the A/P, but IMHO its the quality of the components down the line which really control dependability.
Parts such as
rudder feedback sensors,
fluxgate compasses,
seals in the hydraulic reversing pumps are where you need good quality.
On sailboats a common complaint is that when changing from sail to powering configuration the A/P needs to be course-corrected to allow for the amount of
helm being carried to compensate for
engine torque or sail trim.
On you Twawler look for an A/P that will be robust enough to deal with long term quartering sea course corrections to allow for yaw. A good
commercial pilot should have multiple setting capability in thia area.
Once again IMHO I would go for the reversing pump/ separate ram combo at the
rudder head. If the
steering fails, you can come home on the independant A/P system.
Don't ask me how I know
Hope this helps