A quick search using the word scapa found this thread from a while ago which outlines when you can "expect" to see ships in scapa:
http://www.subsim.com/radioroom/showthread.php?t=108114
Note there are no guarantees as the dates are approximate and there is a level of randomness in the appearance of ships built into the campaign files to prevent thingsw from getting too predictable. Thanks to the hard work of bigboywooly.