I am considering combining a Garmin GPS 72H with a Raymarine ST1000 Tiller Autopilot on my 24ft Trailer Sailer.
Can anyone please advise if the Raymarine ST1000 Tiller Autopilot can be connected directly to a Garmin GPS 72H via the cable supplied with the GPS and will that allow the NMEA function to be used. 
Pete
Thanks v much for the info. I agree that the compatability will be just a bonus and probably won't be used much and visual nav. will always be No.1. Just thought it would be handy to input a destination rather than just a heading. Have ordered the units from the good old US of A and while I prefer to shop local a saving of over $200 (even after postage) is hard to pass up. 
The Autohelm tiller pilots are a very good unit. However I have discovered a problem with my installation that I am not sure how to resolve. I have the autopilot wired into the "instruments" circuit breaker which feeds all of the instruments, chart plotter and GPS unit. When the autopilot senses that it has to make a full lock correction to helm, such as when adrift without steerage, the motor stall current is high enough to trip the circuit breaker. I am then without all instruments until the circuit breaker is reset and instruments turned on. Guess I will have to read the manual to see what the motor stall current is and what rating the circuit breaker is. I sort of imagine that if the same thing happened when relying on the autopilot as an extra pair of hands when reefing in storm conditions or similar it could get rather messy.
There are two main advantages of having your autopilot hooked up to NMEA:
1. On a long leg, if the AP is heading to a waypoint rather than just holding a fixed heading, it will automatically correct for your boat's leeway. This is not much help when running (coz not much leeway), or when very close-hauled (coz it can't deal with wind shifts). But very handy for a long broad-reaching passage. especially in the dark or out of sight of land.
2. If you have your common waypoints stored (eg mooring or marina) and feel lazy/cbf, you can just tell it "home James".
So no big deal, but handy nonethless.
Order arrived AOK on the 10th Feb. though it had been opened by Customs. Saved well over $200. www.jandhproducts.com
On my fishing vessel [which I have sold now and retired] I had a JRC gps dedicated to driving the autopilot. Living on the South coast of NSW and being subjected to the often strong southerly current which we had to cross daily and it varied in strength and direction constantly, the gps set up saved fuel and time. Using a computer nav system kept the navigation separate from the autopilot. The old JRC unit had all the waypoints stored and was easy for the deckhands to operate while I was checking the back of my eyelids. If there was a change of plan I could just call out a number and one of the deckhands awake in the main cabin could do the change. If we were moving along the coast care was needed not to miss a waypoint and cut corners.
The autopilot was driving the boat 99% of the time and the gps was driving the autopilot when we were clear of the coast. The autopilot was used to cross the bar and drive up the river as well. This set up is ideal for motor vessels but I'm not so sure about yachts.
The GPS autopilot combo is constantly calculating the effects of wind and currents and making course adjustments, its is just like drawing wind/current speed vectors on a plotting paper or chart. Sometimes the current can have a greater effect on the vessel and it was not unusual to have sudden course changes of 40 degrees as we passed through current lines. This could have dramatic effects if you happened to be sailing close hauled and suddenly found your sails aback.
I'm a fan of windvane self steering for my yacht and would only use an autopilot for motoring.
I guess what it comes back to is the accuracy and repeatability of a GPS fix and then the very different question of the reliability of that GPS fix translated to a location on an electronic chart. If you are at a location that you want to get back to at some time in the future ie your marina pen, the middle of a bar entrance or an MOB. then the mark button on the GPS will be able to get back there within the accuracy of the GPS system. (generally +/=30 metres but often +/=5 metres). Sit your GPS at a fixed point and watch the GOTO function for a while. As various planets pass over and atmospheric conditions occur the GPS will walk around the error radius. DO NOT rely on the GPS to guide you more accurately than the error radius.
The big difference with electronic charts and GPS is callibration of the chart to the GPS grid. When tied up to the Metung pub jetty my chartplotter shows my boat to be sitting in the public toilet block 200 meters to the South. A similar situation to Shockwave but with less disasterous consequence.
On this cruise I loaded Seaclear onto a mini laptop which was also hooked up to the internet via a high gain antenae. I thought that I had all the charts loaded onto my USB stick but couldn't find the files so didn't use Seaclear. We used paper charts and cruising guides to get an overall visual view of where we were headed. We used the chartplotter with vector charts to zoom in and have a close look at marks lights etc. then planned our route using a combination of waypoints derived from the paper charts, cruising guide given waypoints and electronic chart waypoints. We used the chartplotter to drive the autopilot (at times) and could display all of the electronic data on the TickTack instruments. We used the Navi GT31 as a backup GPS unit , these have a recordable card inside so have a complete backup tracklog of the trip. The GT31 coordinates were plotted onto the paper charts along with our DR just to be old school.
With all of this stuff working I still only feel comfortable when I can get a visual on lights/transits and binnoculars are essential.
