Bracco,
the seeweed looks good but there is one point:
be carefull with rust below the waterline, there wasn`t much rust there because the lack of oxigen.
Of course there was rust on some places even under water, but this rust should be dark, almost black.
By airbrushing some different shades of grey on the hull, you can give the hull a bit more `depth`.
On this pic you can see the variety of shades (and stains) on the hull:
Karel