Jim Donohue wrote:
In many places you use the numbers from last time. Many of the numbers are
published in guides or privately.

Local knowledge is handy.

You can also set up the course to
minimize exposure.

You mean, like plotting a course using piloting techniques?


In general the errors are area wide. You work out the correction from known
objects. You use radar and the bottom to assure yourself you did it
correctly.

You mean, like using piloting techniques?

Go slow when in doubt.

Why would you have any doubt? Don't you have absolute faith in your GPS?

"Jeff Morris" wrote in message
...
Jim Donohue wrote:
In many places you use the numbers from last time. Many of the numbers
are published in guides or privately.

Local knowledge is handy.

You can also set up the course to
minimize exposure.

You mean, like plotting a course using piloting techniques?

I mean like plotting the GPS waypoints on the chart. For a difficult
segment of a voyage I would certainly plot the course even if the primary
navigation is a chart plotter. I would have the waypoints in a secondary
GPS.

In general the errors are area wide. You work out the correction from
known objects. You use radar and the bottom to assure yourself you did
it correctly.

You mean, like using piloting techniques?

You cerrtainly back up your GPS course by what you have available
particularly when the charts or waypoints are suspect.

Go slow when in doubt.

Why would you have any doubt? Don't you have absolute faith in your GPS?

I have far more faith in a GPS, particularly a redundant pair, than I do in
a LOP from a physical target. I have complete faith in nothing. The use of
a GPS still involves risk...little things like entering a waypoint wrong can
play havoc with the best of plans. I generally set up a system where
waypoints are transferred from the chart plotter to a hand held and the the
handheld waypoints are then plotted on a chart. I have twice found courses
that attempted to sail through or very near small islands.

I would also note that dredging barges can appear in the damndest
places...and the radar image can be difficult to understand particularly
against prominent background. Slow right down until we figure it out.

Jim Donohue