Raymarine ST60 Autopilot without GPS Signal

[DotDun]

Originally Posted by Albro359

So a mixup in terminology I think....and this discussion is getting rather pedantic... I'm as much to blame !

I'll share the blame!

[myocean]

Thank you very much for your comments!
Actually I don't know at the moment which autopilot is controlled by my ST60 instruments. It is probably some kind of Raymarine device made between 2000 and 2005. I will check when I am back at the boat.
Can directly I connect a gps even via NMEA or only via seatalk.
I will work with a GPS and Laptop (pobably MaxSea) and most important for me is to have an autopiot which does not loose control under difficult conditions. There is not Chartplotter.
The issue with current and leeway is certainly interesting. So I will try to make the connection.
Would you recommend a specific type of GPS or wouldn't you care?

[noelex 77]

Welcome to forum Myocean.

As others have said giving your autopilot a GPS input will not make it steer the boat any better or more accurately . Not even a little bit.
What the GPS input will alow you to do is to engage track mode. Some people love track mode, others like me, rarely use it.

If you still want to add the GPS It depends on the model of raymarine autopilot you have whether it will accept a direct NMEA GPS input. To use it in track mode the GPS input has to come from the device you are setting the waypoint on.

[myocean]

Thank you noelex 77!
I will take my time to have a closer look at this.

[Albro359]

Connecting a GPS that allows you to set a wayoint and "go to" it will provide the pilot with XTE. When you "engage" Track on the pilot, the pilot will maintain a COG that will get you to that waypoint more accurately and directly than you could helm it.
Because it maintains a COG, it is taking account of leeway and current.
If you don;t have GPS and Track engaged, the autopilot steers to a heading, which means that the COG will be influenced by leeway and current.
So in that sense, it is more "accurate" with a GPS.

[Ex-Calif]

I am really scared to jump into this conversation as there are different specifics on each setup but...

The autopilot is somehat dumb - It doesn't calculate stuff. It is commanded. Normally there are three things that can command the autopilot.

Heading - this is simply the user selecting a heading or often just pressing the "auto" button. The "dumb" autopilot will simply steer that heading.
Apparent Wind - If installed the wind instrument provides a "changing" heading to the autopilot - It is still basically a heading to steer that changes as the Apparent Wind changes

GPS - The GPS (or more acurately gps/plotter integrated unit) sends "CTS" or course to steer. CTS is computed inside the GPS and is based on XTE from a pair of waypoints.

Speed is often used by the GPS to calculate CTS - If you are close to the waypoint, far off course and going "fast" the CTS angle will necessarily be larger.

Having used GPS in flying at much higher speeds this effect is more apparent than on a boat.

How the autopilot is controlled depends on the setup - that is if there is a chartplotter that is receiving GPS input and the chartplotter holds the course etc. In this case the plotter is sending the CTS onto the network which is received by the autopilot. The GPS in a "plotter" setup is usually a "dumb" gps receiver that only provides position info to the plotter. The plotter in this case is where the magic is happening.

I don't know what happens when two plotting devices are hooked up in the same network - I doubt that is a good thing.

In the original question OP asked about more precise steering. The GPS won't improve that. Every autopilot I have encountered has a steering calibration. Increasing the steering sensitivity may reduce XTE but will result in more "hunting" and more work for the autopilot with an increase in load and electricity consumption.

In a sailboat the toughest point of sail for an autopilot is downwind in a quartering sea. But that is the toughest for a human as well...

[transmitterdan]

We have a similar setup with ST6000+ control head. Raymarine has no way to enter a waypoint into the ST control head. You must have a computer for that. Typically you would use a Raymarine MFD but it should be possible to make a PC application do what is required. You will need to connect the PC via a Seatalk converter to the Seatalk bus plus determine if the PC navigation app can drive the sentences needed to make the Raymarine autopilot happy. Personally I would not be happy with that setup for a number of reasons.

Raymarine does not require a GPS for steering by compass as others have already said. Adding just a GPS to Seatalk will not do anything for the autopilot.

[Ex-Calif]

Originally Posted by transmitterdan

We have a similar setup with ST6000+ control head. Raymarine has no way to enter a waypoint into the ST control head. You must have a computer for that. Typically you would use a Raymarine MFD but it should be possible to make a PC application do what is required. You will need to connect the PC via a Seatalk converter to the Seatalk bus plus determine if the PC navigation app can drive the sentences needed to make the Raymarine autopilot happy. Personally I would not be happy with that setup for a number of reasons.

Raymarine does not require a GPS for steering by compass as others have already said. Adding just a GPS to Seatalk will not do anything for the autopilot.

Agree - As a test of my AP I created a "pigtail" for my old Garmin 292(?) aviation GPS / plotter. This Garmin produced NMEA 0183 output. I pigtailed the output into the seatalk network and the autopilot received and obeyed as advertised. - but as stated the AP simply steered CTS as provided by the "brain."

Once again the AP doesn't know "waypoint" - It has no smarts. It just steers as told.

[DotDun]

Originally Posted by transmitterdan

You will need to connect the PC via a Seatalk converter to the Seatalk bus plus determine if the PC navigation app can drive the sentences needed to make the Raymarine autopilot happy.

The S and X series course computers have NMEA 0183 ports on them, no need to convert to Seatalk for these models.