I had to blow up that photo abput 200% to see it , there also looks to be some differences on the trailing edge, the Tubbie 1 looks to come to more of a point whereas the Tubbie2 flattens out more at the rear.
That's exactly what the Blowsion website says.If I am remembering my conversation with Mark at Blowsion (2004), the 2's have that cut out which was supposed to help give more grab and also negate some of the side to side "Chine Walking" that the tubbies gave the RN SJ's....