Some sea charts are just released as KAP files, without the accompanying BSB file. If you run into problems importing the KAP files, there is a way to generate the BSB files.
For example, these New Zealand maps: http://mce66.altervista.org/software.html#Free_Nautical_Raster_Maps are without the BSB files. The KAP files are generated with the MapCal tools (http://www.dacust.com/inlandwaters/mapcal/) and the original New Zealand DIR file is also on the website.
From the MapCal site, download the MC2BSBH tool and run it on the directory with the KAP files. A BSB file is generated for every KAP file.
MC2BSBH chartcal.DIR -e BSB
Normally a BSB file can contain multiple references to KAP files (e.g. detail charts) but I still have to figure that out.