Thanks Felix, I tested it now with: extend-sea-sectors,close-gaps=6000,floodblocker,fbgap=60,fbthres=200,fbratio=0.6,land-tag=natural=background
No errors and sea polygons came back, but the floodblocker blocks still too much. I've tried it with other fb numbers but it still gives the same picture:
http://img404.imageshack.us/img404/3702/nogroningen.jpg
The tested tile you can download at http://mijndev.openstreetmap.nl/~ligfietser/diverse/Test.zip
Minko, I will download your test data and give it a try. If you want to get detailed information what the flood blocker is doing, you should enable an appropriate logging. See http://www.mail-archive.com/mkgmap-dev@lists.mkgmap.org.uk/msg02381.html how the logging.properties file can be configured and add the line uk.me.parabola.mkgmap.reader.osm.SeaPolygonRelation.level=INFO to the logging.properties file. You might also add the parameter fbdebug to the sea-generation options. In this case the flood blocker creates GPX files for each checked polygon and the pro blocking (highways) and the contra blocking (ferry routes) points. Opening these files with JOSM makes it easier to understand why the flood blocker fails. WanMil