Originally Posted by fallard
If you use the Imray-Iolare charts, note that they are not only not to NGA standards, but they are on a different datum than the US charts and your chartplotter, which is undoubtedly on WGS84. Read the fine print on the chart if you want to be precise, although there is only a very slight correction if you want to transfer a waypoint from the chart to your GPS.
In my tests with the chartplotter programs, I was concerned about both datum and projection (though the latter not such a big issue close to the equator), so I carefully verified both. The NGA chart header says it is WGS datum, and the NOAA chart is as well.
I will heed your warning to watch out for the datum on any charts that are on the charter vessel. Are there simple offsets available?