Hi, I have a Simrad TP22 on my SS26 which must now be 11-12 years old. It's given pretty good service although I've had to replace the drive belt, and also the two magnetic sensors in the gearbox assembly. I tend to only use it when motoring, and for putting up the sails when I'm single handed so it doesn't really see any significant load.
I've got a background in electronics and have been asked on a number of occasions to look at various bits of "yachty" electronics. To date I've repaired three Autohelm 1000/2000s and two TP22 including my own, both of which had the same fault.
So here's my two pence worth. Mechanically the Autohelm 1000 and 2000 are the same, and are superior to the Simrad in that they have a recirculation ball drive on the ram which is smoother, more reliable (and more efficient) than the nylon nut and leadscrew used on the Simrad. In this respect the Autohlem is better. Internal construction is somewhat similar in that there's a drive PCB, compass, motor/gearbox and ram. Moisture proofing, and water ingress prevention, is again something that is the pretty much the same for both units. What depresses me is that neither manufacturer make any attempt to protect the components and tracking on the board with a coat of lacquer or varnish. All the components, PCB track, connectors etc are exposed to the air around them so subject to corrosion. To prolong the life of these things try to keep them dry, and keep it in the warm at home over the winter.
The biggest difference (aside for the compass location already mentioned) is how the two units handle a stall condition on the ram. The Simrad has two magnets and two sensors in the gearbox that detect gearbox movement and direction. So if the electronics is calling for the ram to move and applying power to the motor, but the gearbox isn't moving (because it's at end of travel or stalled for some other reason), it will beep and turn off drive after a couple of seconds.
By contrast the Autohlem/Raymarine units have NO stall detection/protection circuitry. When first fixing an Autohlem 1000 I thought this very strange so did a bit of investigation. I found a post where someone had challenged Raymarine about this, and apparently the Raymarine response was that if the ram was stalled, the off course alarm would sound and the skipper would then intervene to correct the situation. What actually happens when you stall an Autohlem 1000/2000 is that they pull big currents from the supply 10-15A or so. If (when?) this happens for any length of time then either the breaker in the supply trips (or fuse blows) or the transistors in the motor drive circuit get so hot the solder melts and they fall off the circuit board. Two of the Autohelms I fixed had transistors rattling around inside where they'd unsoldered themselves off the PCB. I'd guess it takes about 10-15 seconds of stalled ram for this to happen. In both cases, replacing the transistors with new devices (less than £5 for the bits) brought the units back to full operation.
Overall the Raymarine/Autohelm unit does feel slightly better made (and I think is generally more expensive), but the lack of stall protection is a MASSIVE drop off in my opinion. However, once aware of this limitation then the Autohlem unit would probably be my choice because of the better ram implementation.
One final point, the Simrad unit (or at least the TP 22) is quite sensitive to dips in the supply. Like the Autohelm unit, current spikes can easily be 10A when the motor initially starts (or if stalled), and if this causes even a brief dip in the 12V supply the unit will beep, reset, and generally not work properly. I recently had a problem where I thought my TP 22 was playing up, but when I tried it at home on a solid supply it worked perfectly. The issue was traced to a slightly poor contact on the "Autohelm" breaker circuit.
Apologies if I’ve rambled on a bit
John Guess
SS26 Evangeline