Steve,
I'm in the same situation as you, in that I have just sold my pre-NMEA
AH3000 control head, with the intention of buying an ST3000 control head.

I've had two good prices on buying just the control head as I am keeping the
drive motor. Most companies want you to buy the complete system.

Raymarine (UK) have confirmed that the ST will directly replace the AH but
with the added facility of Seatalk. I have the interface from my previous
boat, so will be able to marry both parts of the system into my GPS.

I was intending to upgrade to an ST4000, but believe that I would have to
install rudder feedback, as well as buying a fluxgate compass unit to feed
the 4000. With just replacing the AH3000 with the ST3000, that will be all
there is to it.

regards,
Philip, s/v Oyster


"Steve" wrote in message
...
I'm in about the same situation, having a pre-ST autohelm 3000 that is
under
powered and doesn't take NMEA input. Otherwise it works fine in calm water
with the course set manually..

I have already found a solution to the increase in power, however I'm
still
searching for an upgrade to the control head.

Be advised that none of the pre ST autohelm/Raymarine pilot will except
NMEA input.. Even the Z80 interface seems to dislike the current 0183
formats.

Then we get into the ST models. Even some of these early ST models still
required an interface to convert the NMEA to SeaTalk before it goes to the
AP..

I investigated a ST5000 on ebay that had a location for the NMEA
connection
and the markings were molded into the case, but the connector pins holes
were empty.. Must have been a very early release..

Then there is the problem of your drive motor clutch.. I believe that the
ST5000 is the first model to have a clutch control in the control head..
Here again, I would approach this with caution since there are going to be
control heads sold for tiller pilots that don't require a clutch release.

I would recommend staying away from the current generation since the
control
head don't necassarily have the course computer in them, just some
secondary
circuits, display and buttons. The course computer is incorporated in some
other nav station equipment..

I think your approach is correct as you have evaluated each of the system
components and determined what to keep and what to abandon.. Your boat
size,
like mine make it nearly impossible to purchase an off the shelf AP
system..
My boat being 13.5 ton and tiller steered.. Even the largest tiller pilot
system comes up short.

Good luck.
--
My opinion and experience. FWIW

Steve
s/v Good Intentions