Hi Eric. Re progress on the autopilot question, yes, it appears that the Raymarine ST4000 Mk2 wheel-mounted rudder drive unit will indeed work with the Simrad/B&G NAC-2 and NAC-3 autopilot computers. And no, there’s no whole-ship instrument replacement kit that I know of, but I’ll give you my thoughts on that below.
Concerning the autopilot, the ST4000 was originally installed as the rudder drive module of an older Raymarine SmartPilot X5 Wheel system. The ST4000 bolts to the spokes on the ship’s wheel and is pretty much nothing more than big drive belt and a reversible 12vdc motor with a sprocket on its shaft. The first piece of evidence that the ST4000 can be used in an upgrade came from Raymarine’s website documentation, which specifically says that the ST4000 will work with Raymarine’s new Evolution Autopilot system. Second, a B&G tech support rep told me on the phone that the NAC-2 and NAC-3 can drive any reversible DC motor within their power capacities. And for confirmation and comfort, I found on the Jefa Steering website a sprocket drive motor with an autopilot computer compatibility table that lists both the Raymarine Evolution and the NAC-2/NAC-3. So I’m now planning to go ahead and buy the NAC-2, since it’s less expensive than the NAC-3 and can handle the relatively low 5-amp power draw of the ST4000.
What’s actually going on with these modular Raymarine and Simrad/B&G autopilot systems is that their computer units all use DC current at a fixed voltage to operate the rudder drive motor, controlling the direction of the motor via the polarity of the current and varying the torque and speed of the motor by using pulse width modulation of the constant 12-volt (or 24-volt) output to change the effective voltage seen by the motor. The computers all have only two pairs of terminals for their rudder drive outputs, one pair for the clutch and one pair to operate the motor. After the computers are calibrated they’ll appropriately drive any reversible DC motor connected to the motor terminals. (The ST4000 has a manual clutch, so I won’t need to use the clutch terminals on the NAC-2.)
However, one important thing to note is the need to include a rudder position indicator in any of these autopilot systems. The NAC-2 will take rudder inputs either from a resistance-based rudder feedback unit or a NMEA 2000 data-based unit. The Simrad/B&G data-based RF25 unit is short enough to fit in my boat, so I’ll use the RF25 with the NAC-2.
This brings me to the second part of your question. I haven’t purchased the autopilot system yet because I’m currently focused on installing the various pieces of B&G equipment that I already bought. These consist of two Triton2 displays, a DST sensor, a GPS/compass, a wind instrument, and some NMEA 2000 cable and connectors, all of which were included in the “B&G wired wind package with two Triton2 displays” that came from Defender Marine. In addition to the NAC-2 autopilot components I want to add a chartplotter (probably a Vulcan 9) and a WR10 bluetooth remote control for the autopilot. Also, B&G strongly recommends adding a physical standby key to the autopilot system, and that physical key can be either the Triton2 Autopilot Controller (which is a $300 keypad) or a simple momentary pushbutton switch. Since I’ll have the WR10 remote I’ll probably skip the keypad and go with the pushbutton to save $300 and be able to make a smaller mounting hole in the boat. I might also add a ForwardScan through-hull sonar transducer at some point since the Vulcan chartplotters have a direct plug-in for those transducers.
If anyone has additional thoughts on any of this I’d love to hear them!
Mike