I know this is an old thread, but here's a tip. When I read the informative OpenCPN
help file linked above, I was a little boggled trying to translate that into the areas I was interested in. Here's something much easier:
1. Zoom out to the general view you are interested in (in OpenCPN)
2. Switch OpenCPN into non-quilted mode (F9) (you know you are there when the rounded bubbles showing chart coverage at the bottom of the screen
become squared bubbles).
3. Right click on the map and select CM93 Offset Dialog
4. Note the numbers in the left-most column. These are the folders you want to get for the area you are looking at.
For example, using this procedure with the chart showing US East Coast
, Gulf of Mexico
results in 4 chart areas: 02700720, 02700840, 03900720, 03900840. Copy these folders, and the files in the root directory, and you should have coverage for just that area.
In general, you can greatly reduce the size of your CM93 data file, if you limit the areas of interest. Charts
for the entire world covering only 40N to 40S are 1/3 the size of the whole CM93 folder. (370 MB vs 1.x GB). These are the folders 0150xxxx and 0270xxxx.