User blog comment:Eightynine!/A fun ending for one piece/@comment-3986064-20121215192253/@comment-3986064-20121216020005

He can turn into a freaking boat that carried Nami and Robin in a chapter cover, that's proof enough that he has got the means to move through water without sinking. Also before the TS he could swim more than good enough, I see no reason why he couldn't now as well.

One final tip.