It´s supposed to lower ship maintenance to 10% but didn´t lower it at all. I was doing some testing with reform decisions since there wasn´t much detail provided by the reform decisions menu (btw, thanks to whoever wrote the wiki site about it), while I noticed this. I raised an x amount of fleets, then ran the game for a while without doing the reform to see the cost, and then did the same with the sea-bound doctrine chosen. The cost was exactly the same. I loaded the game in between.