Humphrees are nice indeed, but I do agree with CaptJ in that Arnesons don't have an issue with tracking. IMTRA sells a product called ZipWake that is an interceptor system, but is considerably less expensive than Humphree's. I've seen them on some Pilot Boats and also some higher speed Yachts, and the interface is very nicely developed.
The entire thread has been taken off track due to one person citing an issue apparently with a Simrad autopilot and attributing that and hearsay and other to a conclusion that there's an Arneson problem with tracking. There isn't, so case dismissed. I'm not a fan of surface drives but this is not one of their problems or a reason they aren't my preference.