I just read through the Arabasta Arc the other night, and it got me thinkin' about Akoji.
He turns to ice and rebuilds himself if he's shattered and what not, right? Well, that's not much different than Crocodile turning to sand, so why wouldn't the same stragety of using water / blood on your fists / body, do the same kinda damage?
I mean, I dont think the water worked just cause Croc was sand, I think it worked because water is the weakness of the Devil Fruit users. Maybe when water touches their skin in nulls the ability of Logia Fruit users to become their element.
If that is true, wouldn't the water on fists strat give Luffy the ability to damage Akoji?