DO IT!
Biggest thing I worried about on a smaller boat was their head bobbing around at speed. Ive seen adults get hurt hitting waves wrong. So, on the smaller boats, we take it easy. At least until their sitting up pretty stable.
We have a 31' in Boston and we are able to bring the car seat aboard for them to stay in. Then mainly worry that their out of the sun and well ventilated from fumes etc.
My 1st son was born nov so we had him out the next June. My 2nd son was March this year, and he will be out this summer. Hopefully, this weekend!