Richard Casady, in article 47b6d18e.1524399671
@news.east.earthlink.net, says...

I was under the impression that GPS results are referenced to the
location of the antenna. So what does heel have to do with it?

When you are heeled over, the antenna, if up the mast, will be
over to the side somewhere, some distance from the boat
centerline where it will be giving an incorrect position
report for the boat. Since heel isn't constant, the error
introduced by heel would be variable.

Not that you should be using the position information reported
by GPS to that level of accuracy anyway :-) However, there
have been several GPS assisted collisions with fixed landscape
features, so perhaps that isn't true anymore?

If you are pitching and rolling, the antenna will be moving
relative to the boat so the GPS will include that motion in
with the boat's forward velocity in its speed calculation.
---
One problem with mounting the antenna at deck level, under the
pushpit, is that from a dinghy, it looks too much like a
handle to help getting on deck. If on the pushpit, it can get
knocked. I have mine under the GPS structure which has no
reported signal strength implications. It also isn't a
visible "I've got a GPS available for stealing" signal...

--
JohnW.
Replace the obvious with co.uk in 2 places to mail me.