I thought Remi would be much more apprehensive about riding a boat, what with the huge amounts of running water surrounding her.
You know, as you bring that up...
I always theorized that once the maidens crossed the Hakurei Border they would a) fade away or b) become effectively human (abnormal appearances remaining, of course, hence 'effectively' instead 'completely'. Just in case anyone may get confused, lol) the further away from the border they got.
Considering how much comes in (and, apparently, out of) the border, I think it's safe to say that option a) isn't much of the threat it seemed to be. But, I've always favored the thought that the fantasy that is their abilities and powers would remain or diminish as determined by how far away from they are from the border and, naturally, Gensokyo.