On a Parker 21 or 235, go for the Simrad TP10 or TP20, not the Raymarine ST1000!

I've had a Raymarine one for years (well, I've got through 3 now), but it finally gave up last year (horrible corroded mess inside!) But it was never much use when the engine was in the well, as the compass is on the inboard end of the tillerpilot, too close to the engine, and gets a lot of magnetic interference. This only became a problem when I changed engines from a Mercury 2-stroke to a Yamaha 4-stroke.

But the Simrad ones have the compass at the outboard end, further from the engine, and seem to work fine. I'm glad I changed!

James Hamilton
Hi just to confirm, I know Peter Scrivens has the same problem with his Raymarine tiller pilot, (while, although I have issues with it's control algorithm for my 235), the Simrad has been mechanically reliable and is fine with the engine running.
Ken Surplice

Hi Geoff, I’m sorry to learn that you are in administration 😂.

This is the first time I’ve seen compass location being a deciding factor in choosing an autopilot. Very interesting.

For anyone owing a tiller autopilot, I highly recommend a cover to help keep the electronics dry

On the corrosion issue, I learned of and purchased from eBay a waterproof cover for my Autohelm tiller pilot. In practical boat owner forums many report problems with water ingress. The cover stops that and gives you a more reliable and longer lasting setup. They’re still for sale. The price is £15. My cover is well made, fits perfectly and show no sign of fading or degradation after being in use for many years. There’s also no need to remove the cover when the sun comes out, as the autopilot doesn’t overheat with the cover on during warm sunny days. And no, it’s not my aunty that makes them 😀. 

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

Ken Surplice
Thanks John. That's very interesting. Not a hint of rambling, just good stuff to know. You mention lack of lacquer protection. Does this mean I can and should open up my ST1000 & ST2000 units and spray the circuit boards with an aerosol lacquer? If so, do you have a favourite spray you would recommend please?
I have a Raymarine St1000 which works well and is I believe based on the original Autohelm Tiller Pilot. It worked well until that is I started the engine which caused it to go crazy because of the magnets flying around inside the engine. I found quite a bit of information on this problem and in particular advice from Raymarine as to how to resolve. The St1000 has the capability of a simple interface with a remote compass which provide a stable heading reading for the St1000. I purchased on Ebay a second hand ST40 compass instrument and Fluxgate compass and with simple wiring to the ST1000 socket now have a remote compass which should stabilize the system. I have yet to try it out on the water but it all seems to function. A further reference to this problem referred to disconnecting the Fluxgate compass within the ST1000 and relying on the ST40 only.

I'm looking forward to trying it out in a couple of weeks time but am expecting it to work as by all accounts it solves the problem of motor interference.

With regards to protecting the PCB(s) from moisture what you really need is conformal coating. Ambersil and Electrolube both make suitable spray products, readily available from eBay, Amazon etc. You can also get coatings that are applied by brush. If using aerosol, obviously be ULTRA careful not to spray it into any moving bits (compass, gearbox etc). Possibly the safest approach would be to remove the PCB(s), mask any connector pins and spray a couple of light coats.
John Guess

SS26 Evangeline


I was recommended to get a cover for my ST1000 autohelm and bought one of these. 

Although it didn’t get a lot of use it was good to be able to keep the water away from the selection buttons and hopefully help to keep the unit dry. It was well made, easy to fit and didn’t hamper using the selection buttons.