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Catalina/Capri 25/250 Sailor's Forums

General Sailing Forum

Tillerpilot help?

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High H2O
1st Mate

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35 Posts

Initially Posted - 01/15/2005 : 21:56:57

I'm in the process of installing an ST 1000+ on my C250 and have a question about wiring. I want to interface a Garmin Map76s gps with the tillerpilot. I have consulted both the gps and autopilot installation manuals but found conflicting descriptions of how to connect the NMEA data wires. Has anyone out there been through this and possibly offer some help?

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Arlyn Stewart
Master Marine Consultant

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USA
2980 Posts

Response Posted - 01/16/2005 : 09:00:36

Hi Ric,

I will take a stab at it though my installation was with a ST4000 wheel pilot.

The NMEA line on the autopilot probably has two connections marked plus and minus whereas the gps probably has two NMEA wires marked data in and data out.

The autopilot makes connection to the data out of the gps but none to the data in. Therefore make the NMEA out of the gps to the data plus + of the pilot. Thats the easy one and you probably have it configured correctly.

The data minus - of the auto pilot is more confusing because there is no corresponding wire on the gps, it however goes to the gps ground wire.

Now here is the bugaroo... don't be tempted to think, ahhh... the gps is grounded by its black wire to the boats ground bus to make the full circuitry for the 12v supply and therefore all thats needed is to make the data minus - of the autopilot to its black ground pigtail and let the ground bus serve as the path. It ought to work and in some cases it does but very often it either won't work at all or operation is irradic.

The data minus - of autopilot then makes to the gps black gound wire at the same point which it grounds to the boats ground bus.

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lcharlot
Master Marine Consultant

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Antigua and Barbuda
1301 Posts

Response Posted - 01/16/2005 : 10:47:25

I bought a Simrad TP2000 last winter and had the same problem you are having, that the instruction booklet was very unclear on how to connect the tillerpilot to a GPS. As I recall, there were three or four possible different combinations of wiring connections between the two devices, and I had to try them all before finding the one that seemed to work. Unfortunately, there is still something wrong; the tillerpilot seems to connect to the GPS (a Garmin model 168), but won't follow the GPS's route or track, when the boat reaches a turn point in the route, the tillerpilot goes to hard-port and just spins the boat in a circle. I have only been able to get this tillerpilot to work in the simplest mode, the basic compass course. The auto-tack feature doesn't work, and as I said above it won't follow GPS steering commands. It has been a major dissapointment and since I mainly wanted it to use as a GPS autopilot, it has been of almost no use to me.

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High H2O
1st Mate

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35 Posts

Response Posted - 01/16/2005 : 11:02:23

Arlyn,

You are right on target as usual. One manufacturer calls it + and - the other calls it "data in" and "data out". I was thinking + = "data in" and - = "data out"... but thought I would pose the question here before going any further with the install. Thanks!

Ric

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Arlyn Stewart
Master Marine Consultant

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USA
2980 Posts

Response Posted - 01/16/2005 : 12:55:02

Ric, yes.... its confusing...as the autopilot does not even have an NMEA data out, it is a data ground. However, I can understand them not calling it a data ground because of the problem that results if it is taken to ground at the installation of the pilot.

I do not know exactly why it doesn't work that way... perhaps it forms what is called a ground loop or experiences data corruption do to noise on the ground bus.

Larry, I've no idea if the Simrad acts similar to autohelm... but I know from several who I've helped as well as my own installation that the autopilot minus wire if taken to ground at the pilot will be unpredictable in that sometimes it won't work at all and other times is flaky.

It does not go however to the data in of the gps but rather to the ground wire of the gps to complete the data out circuit.

Think of it this way... if the installation has only a gps and a pilot, it is a simple installation as there is only one way communications, as pilots don't talk, they just take instructions.

A more complex installation where devices talk back and forth, need both data directions established on an NMEA bus. Examples of this are if one has a base mounted gps and its desired to load it from the lap top or another hand held gps. Then, the gps must have its data in wire connected to a bus.

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The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.