azudo said...

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

Pete, This arrangement should work. I have an ST2000 that is driven from an NMEA hub linked to my TikTak wireless instruments. The NMEA hub also accepts GPS signal inputs and broadcasts these to my Geonav chart plotter, wireless instrument readouts and back from the chart plotter to the Autopilot. The pilot also accepts wind instrument steering instructions via the hub. I also have a Navi GT31 GPS unit that is linked to a laptop chartplotter using the NMEA output piped down the supplied USB cable with the appropriate device driver software. I intend??? to link the NMEA output (via USB cable) of the laptop chartplotter into the NMEA hub as a backup plotter. But that is where our problem becomes common. How do you identify the signal wires from the output device and how do you physically connect the wires/devices together. I have purchased a USB socket which has a short cable tail with little gold plated pins. these in theory can be connected to the USB hub or in your case the NMEA inputs to the autopilot. Just have to figure which of the 5 wires is 5 volt which is NMEA +ve and which is NMEA -ve.
I would in reality suggest that you don't need the connection. I in actual fact only use the autopilot to steer a compass course from its internal compass and adjust the compass course by +/- commands based on visual navigation. Its great in theory to have all of this stuff interconnected but other than hours of amusement working out how to get it all to work there is not much practical use for it once you get it all working. I still put the sails up and sail by feel.

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.

Order arrived AOK on the 10th Feb. though it had been opened by Customs. Saved well over $200. www.jandhproducts.com

frant said...
At a later stage I rewired the power supply from the pilot direct to the battery bank with a 20 amp in line fuse which has solved the problem.
For the big picture steering with the pilot from the GPS is fine. However when you get to tricky bits of navigation I will always rely on manual inputs from visual fixes to the course over GPS generated course signals.

Frant, I think you have given all the reasons why on a yacht an auto pilot is better fitted as a stand alone unit.

They are very handy for holding a heading when the crew have other things to attend to like sail changes or pulling the anchor, cooking a feed or making a brew.

I think the best set up for an auto pilot on a yacht is "steer to compass or steer to wind".

There is no substitute to keeping a good "look out" and good "chart work", be it assisted with GPS or not.

If sailing single or short handed, an auto pilot is invaluable as a "navigation aid" only. It is not something one can use in a "court of law defence situation".

Personally I find that if a yacht is sailing in a reasonable breeze and doing more than a few knots, steering it is never boring and I can enjoy doing it for up to 12 hours at a stretch, with short breaks, fairly easily.

I do not advocate that situation but if necessary, it is certainly do able.

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.