Here is some data acquired many years ago (source forgotten):
Numbers of ships arriving and losses in North Atlantic convoys inbound to Britain (ships arriving/losses)
1939 700/5 (.71%)
1940 5,434/133 ((2.5%)
1941 5,923/153 (2.6%)
1942 4,798/80 (1.7%)
1943 5,667/87 (1.5%)
1944 7,410/8 (0.1%)
The most comprehensive inet source on U-boats is
http://www.uboat.net
Please take a look Tony, especially
http://www.uboat.net/technical/shipyards/ for the number produced by each shipyard.