It sounds strange, and should not have been necessary, but since the people behind OpenSeaMap havn't been much of a help of documenting their data model (a few scattered wiki pages with not much readable structure is not documenting). The result have been that I have looked through the tools they have provided (Harbor tagging preset for JOSM and OpenSeaMap Editor plugin also for JOSM), which have given me something more useful to work with, and than started to search for common values with taginfo. The result have been that I have managed to structure their data much better. Things I tag with my reverse engineered data model actually start showing up on OpenSeaMap, something that proves that I am getting closer to the data model.
There are still a lot of things that I cannot get around, though it might be missing from their data model altogether as well. Taginfo doesn't return to me commonly used combination to these tags, as they still havn't enough occurances in the database. That means it is hard to know how to distinguish different types of restricted areas from each other, for example.
Another thing I am wondering about is how to get notes on objects that can show up in separate information boxes depending on map presentation. At the moment I am using note=
My JOSM preset and MapCSS for INT-1 will be updated when I get a chance, probably in a months time (they have been heavily edited compared with the ones on my web page).