Autopilot turning too early for track course

[stevemitchell]

I have a p70s, EV1, and an ACU-100 connected to a mkII wheel pilot. Controlling all of this is an es78. All are running the latest and greatest software. They are all connected via SeaTalk, which is also connected to a NMEA 2000 network. Speed through the water is provided by a NMEA 2000 Maretron DST110 triducer. A complete network diagram is attached and also available at https://sailbits.com/grace/

Using a manually created route, or one via Navionics Autorouting, the MFD is advancing to the next waypoint in the track/route too early, sometimes dangerously so.

This happened 6+ months ago as well, and I did a complete factory reset, dockside wizard and commissioning, and changed the speed source to SOG, and things worked for a while. I think I found a post on the old forums or elsewhere that gave me this guidance.

With this configuration, should speed input be set to SOG or to the STW provided by the DST110? Is this the cause of advancing too early?

[Chuck - Raymarine - Moderator]

Welcome to the Raymarine Forum Steven,

Q1. With this configuration, should speed input be set to SOG or to the STW provided by the DST110?

A1. Should the autopilot be interfaced to a properly calibrated and correctly functioning source of speed through water (STW), then it would be recommended that the autopilot be configured to use speed through water rather than speed over ground (SOG) as its speed data source. Proper operation of the STW sensor may be checked by operating the vessel under slack current conditions and then verifying that STW and SOG are close in value. Use of STW rather than SOG will permit the highest level of autopilot performance, particularly for slower moving vessels which may be operating under conditions of leeway (current and wind).

Q2. Is this the cause of advancing too early?
A2. Negative. Waypoint arrival is determined by a configuration setting within the navigational product (ex. MFD, GPS display, computer running navigational software application, etc.) which has been interfaced to the autopilot. Within the settings of most navigational products, a setting is available for specifying the radius of the arrival circle around a waypoint/cursor position which is being navigated to. The default arrival circle radius setting for Raymarine navigational products is 0.1nm (approx. 600'). For owners of a/c/e/eS/gS-Series MFDs operating with the final release of LightHouse II software (v19.03), the command sequence which will permit the operator to configure this setting is HOME->SET-UP->ALARMS->SETTINGS->SAFETY ALARMS->WAYPOINT ARRIVAL->WAYPOINT ARRIVAL RADIUS.

[stevemitchell]

Thanks very much for your quick and, as always, detailed answer Chuck!

I originally had STW instead of SOG set in the autopilot and had read something on the forums or elsewhere (posted by someone else, not yourself) that SOG was a better value even for a sailboat. I'm glad to hear that STW is the correct value, as SOG never made sense to me.

I have seen a discrepancy in my STW vs SOG in a slack condition, and the boat is being hauled in a few days for bottom cleaning and paint, so I will check for growth and also re-run a calibration on both the autopilot and STW instrument to make sure there are no issues there.

I will also look into the arrival alarms and see if that is my issue as well.

[Chuck - Raymarine - Moderator]

You're welcome.