I'm not sure if it has been posted already, but here are a number of interesting tools made for Silent Hunter I that should be useful for SH IV as well!
http://www.subsowespac.org/downloads.shtml
In the lower right corner there is a set of printable slide rules ("Manual Tools With Guide")
http://www.subsowespac.org/downloads...plusmanual.zip
There are some other neat things available. I didn't check everything out so far!