As Jersey is split over 4 QMID 11 areas I will create 4 polygons in Google Earth, each relating to one QMID 11 area. As you can see below, I have traced out the outline of the coast for one of the QMID 11 areas already.
I then used the FSX_KML program to create a water mask for this area that I can import into SBuilderX to create the necessary water mask. Firstly you need to run the prefsx_klm program to correct some geo-referencing, then just open up the coastline .kml file from Google Earth and add a water attribute.
FSX_KML then outputs a shapefile (.shp) which you can import into SBuilderX. This is important and useful because the water mask needs to completely fill the relevant QMID11 rectangle, which can only been accurately referenced within SBuilderX. Once imported into SBX the polygon required only a little amending to cover the entire QMID11 rectangle (minus the land!), and looked as follows...
This process will be repeated for each of the QMID 11 areas until the total island water mask is complete.