I would think that for a baby that age, one room is not that different from another room, so it being a boat would not be a big deal. As a bonus, the gentle rocking motion might (
might, mind you) have a soothing effect, assuming reasonable weather.
Then, of course I might be full of crap; because I have
0 (zero) experience on this question.
Best of luck, I bet the grandparents will probably be aghast....
a baby,
where ???? on a
boat???????