Garmin 3010C, AIS, and heading-info

Hi,

I recently acquired an AIT250 AIS-transponder and connected it
to my Garmin 3010C chartplotter.
The AIS heading-line in the 3010C is configured to 10 minutes,
as is my own heading-line.

However, many ships do not show a headingline, although they are
moving. On the laptop, with SeaClear, these ships do show a
correct headingline.

After further investigation, it looks like a headingline is only
drawn on the 3010C when explicit heading (and rate-of-turn) from
a (gyro-)compass is sent out.

What I observed:
- when the ship sends heading-info:
a headingline is shown, and both triangle and headingline
are depicted in the direction of the heading-info.
- when no heading is sent:
no headingline is shown, but the triangle gets its direction
from the COG (Course over Ground from the GPS).
- SeaClear uses for the heading-line the heading-info when available,
or COG else, which sounds reasonable to me.

Many ships with Class-A AIS appear to not provide heading-info, and I
have not seen a single Class-B AIS signal with heading-info up to now.
All ships, observed sofar, do provide the GPS-info: position, COG, SOG.

As the headingline is very handy: on sees immediately whether a
collision is oncoming, or whether you'll cross the other ships
course-line minutes before or after the other ship. That the Garmin
does not show a heading (or course) line in many cases seems very
unfortunate to me.

Is there a compelling reason that Garmin does not use the COG for the
headingline, but does fall back on COG for the triangle, or should I
file a bug report to Garmin?

regards,
-- ted

Actually: IMHO, the most sensible thing to show is:
- a course-line, direction based on COG and length on SOG;
- a triangle, based on heading when available, else COG when the
ship is moving more than a few knots, else a circle.
But perhaps there are good reasons not to do that?