What about coastal ironclads based on either the Confederate or Union models? With the shallow waters around the coast they would seem to make sense for port defense, especially around Galveston.
Scrapped in China in 1987 after being blown aground by a typhoon in South Korea. She only did one trip through the NW Passage, second one was apparently blocked by ice and then Canadian concerns about sovereignty and the environment ended the effort and they built the Alaskan Pipeline instead.
K-Ship Profile, lacking in detail http://i49.photobucket.com/albums/f252/CanisD/Never_Weres/Airships/K-Ship.png A good book to check out is US Navy Airships by James R. Shock, available here: http://www.airshiphistory.com/index.html/Books/US%20Navy%20Airships%20detail%20b10003.html I have the softco...
Considering her hull shape, you'd probably get 4-5 knots extra out of her at best. You could probably squeeze a little more speed out of her if you fitted a new bow and stern like some of the Japanese and Italian rebuilds, but that would increase the cost considerably.