We have the same fixtures. The original 12" flourescents were pathetic. We replaced them with 12" LED light strips from Lunasea. Here is a post I did about it in 2012.
More Light, Less Power | M/V Archimedes – An Old Grand Banks 42. They have worked flawlessly since we installed them. Superbrightleds.com has a few options that might work also.
https://www.superbrightleds.com/cat/rigid-light-bars/