No matter if there is a performance degration it would be good to have a method clockwise(List<Coord>) because creating a Way object to check that is also a workaround. I think Java2DConverter is not the best class for that because there is no direct relation between the clockwise test and the conversion to java.awt.* objects. I would prefer either the Utils class, the Way class or a new OsmUtils class.
Reg. performance: I did not measure it. In most places that I've changed the clockwise() method was just used to determine a file name, so I/O performance would be the bottleneck. I think the Way class is a good place for it, so I've changed that. There is now only the PrecompSeaMerger which might show a performance degration, but I don't expect measurable changes. The area.intersect() methods are copying the ArrayLists much more often, so one more copy action should not cause problems. Gerd