NavList:

Lu wrote:
>
> Were you using the GPS's indication of CMG or bearing to a distant mark?
>
> Hopefully you've seen all the subsequent posts, but basically we've all
> said CMG is NOT a reliable instantaneous heading indicator, but bearing
> to a distant waypoint is (assuming you're pointing at it)

A bit of both Lu.  All the good landmarks at Michigan City are in close
proximity, so at some points SOL.

It was a very quite say wind and sea wise.

As a sidebar one GPS was set to magnetic and the other to true.  Did the
math later.  The purpose of that was to compare (a fool's game as it turned
out) the two GPS readings to determine if the GPS was using a lookup table
for true-to-magnetic conversions or downloading the information from the
satellites.

By default the GPS's were reading out COG when not using a bearing to an
object (most of the time).  Bearings seemed to be steady. Determining
direction, even if COG, was insanity. I did my first charts and  diagrams
using the raw data, and the GPS readouts vs the two compass readouts as a
sanity check.  If they all pretty much matched it was assumed the data had a
sporting chance of being usable.

We also noted time, so we could go to the Great Lakes site and look up any
currents at the time.:

http://www.glerl.noaa.gov/res/glcfs/

I factored in set and drift for my second pass at Excel data and charts, and
Napier Diagram.

In the final analysis, the whole exercise was pretty much garbage in,
garbage out.  It did point out two problem areas, 120d and 300d which
opposed each other as might be expected, but did not yield what I would
consider to be a usable deviation diagram/table.

Robert's question and the responses came at an excellent time for me.  The
more problems I can solve for the owner, the more frequently I'm invited
back ;-)

Bill




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