During the 1980's while I was in a C-141 USAF Reserve outfit I came across an article in "Airlifter" which I believe was military publication. The article was about some research that was being done with a C-130 (HOW-Hercules Off Water) model powered by four Supertigre engines. The bottom of the fuselage was covered with a typical seaplane hull with the required step configuration. Engines were mounted higher than normal above the wing to be kept out of water spray. The unique thing about this aircraft was the retractable "ski" (this is the only way I can explain it) jutting out from the bottom center of the fuselage. As I said, this device was retracted once the aircraft was airborne. I'm not sure who did the research, but it may have been Lockheed. I would have to go back and find the article again.