Very nice sub Denodon. In fact, most of the designs I'm seeing in this challenge are very good. This is becoming a great challenge.
I was just discussing AIP systems with Obsydian Shade the other day. Depending on the particular AIP you go with, you probably wouldn't have much trouble fitting them in a sub that will meet the specifications of this challenge. For instance, the Singaporean Archer-class subs were launched as the Swedish Vastergotland-class. Originally, they were 48 meters long, but later had a 12 meter hull section put in that included a Kochums Stirling AIP, which lengthened the hull to total of 60.5 meters, which is still within the limits of this challenge. If you design a sub from the outset to have an AIP it could probably be made even shorter. The Stirling AIP itself is no bigger than say a medium diesel genset and then it requires several bottles of compressed helium, nitrogen, and oxygen, which could be placed outside the pressure hull of the sub. I don't know how large the proton exchange membrane (PEM) AIP system used on the German Type 212 is, but it's probably not too much bigger considering the Type 212 is shorter than the Archer-class subs at only 56 meters. Below is a link to the Kockums official website that explains their Stirling AIP and shows some decent pictures of its size.
http://www.kockums.se/en/products-servi ... ip-system/