For those of you wishing to commercialize your psub design, Graham Hawkes
was granted a US Patent No. 7,131,389 (www.google.com/patents?vid=USPAT7131389) for a personal submersible. There are 89 claims, the first sounding a lot like Alec's original design for Solo which included no ballast tanks and an inverted airfoil to submerge. My guess is that this is more for marketing as it is not a very general patent. Filing date was Jan 22, 2004 and issue date was Nov 7 2006.
Cliff