I had my daughter out when she was 7 months.. The only reason we waited is because he was born in mid-October and the boat was already out of the water.... We're safe and sensible.... I agree about the heat, that was the biggest concern of all!
We boated the whole summer while she was pregnant. I didn't travel the ocean with her so we basically ran up and down the rivers and out into the bay. On Saturdays it was my day and I would make ocean runs with my buddies and on Sunday's I spent the day with my wife.
We have a 2nd baby one on the way, due in April (find out the sex tomorrow).... I'm not nervous about taking the kid out on the boat, that's easy, I am nervous about having a 2 1/2 year old running around with a new born in my wifes arm while I'm driving the boat and controling the 2 1/2 yr old.
I bet we'll have some stories to share and I'm sure it'll be a handfull but I wont let it stop us!!! Worse case scenario I'll grab my sister or have grandma watch the newborn while we go out on the boat with my daughter
As for myself, I was on my parents boat at only a few weeks old, we were a total of 3 kids.