A couple of points:
1. Big prizes only show up at very specific times in Scappa Flow. They are listed on the following web-site (if you want to look):
http://edseek.com/archives/2005/05/0...urvival-guide/
Waiting around near, or in, "The Flow" outside these very specific dates is fruitless. It is also gonna get you sunk, especially if you attack the small warships while waiting.
2. Diving to 50 meters inside Scappa Flow will cause you to strike the ocean floor. The water is very shallow in there...be careful.