I believe that is intentional.
Check the readme file.
The Hull Interity percentage was removed in an erleier version of SH3Cmm and/or RUB.
Makes for interesting times when you start wondering just how much damage you have taken. The percentage is shown in the end of patrol report.
Once got rammed by a Coastal Merchant (my fault), and then hit the sub nets on my return to port, which resulted in flooding, and damaged hull sections. At the end of the mission I was still at 86%. Another time I took what I thought was relatively minor damage as the result of a fighter bombing me on the surface; got back and found I was 16%!
Does spice the game up.
