On Sun, 27 Jan 2008 12:08:31 -0000, JohnW
wrote:

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.

Well yeah. I dismissed that kind of thing as too trivial to worry
about.

Not that you should be using the position information reported
by GPS to that level of accuracy anyway

I think that when feet matter, eyes should be on something else, the
world, the sonar, the radar, something. Maybe even an occasional
glance at the engine gauges. Basically GPS gives position. Mariners
used to find that out once a day, with the sextant, to an accuracy of
no better than half a mile. How soon we forget. Soon third world
despots will be able to disappear the system. I am hanging on to my
sextant, just in case. Iran with ASAT?

Casady