DS was born in June, and was boating (albeit VERY sedately) by August. Teeny Tiny PFD, and a place to rest and chill on my parent's boat.
I think, that with like everything, common sense should rule. No wake jumping, no going out in 8 foot seas, etc. But for a few leisurely cruises, you should be fine. My bigger concern would be a place for the baby to get out of the sun, since she is still a tad young for sunscreen, and the sun out on the water can be brutal.
I saw her on the other thread, she is a cutie pie.
How is your daughter doing?
Debbie