I would recommend staying close enough to land that you can get back in quickly in an emergency, but aside from that, I don't know why they would have a problem. You can even fly at that point in your pregnancy, so why not a boat?
I am only 15 weeks and took a weekend vacation with some friends. I asked my doctor as well. Her concerns were minimal. No lake/pond/river water because of the bacteria and lack of heat to kill them. And to make sure I drink plenty of water and suggested I bring some light snacks.
I didn't go into the water. But I had a great time hanging out on the boat and stayed cool and hydrated and kept the sunscreen at hand.
Definitely talk to your doctor. See what he/she advises. And if it's a green light, enjoy your vacation and be safe. Good luck and have fun!
I went on a caravan and snorkeling at 31 weeks. Boating has little to no risk unless your going scuba diving or across continents. Have fun!!
Call ur Dr and ask. I don't see why it would hurt you or her. Now if u were renting a speed boat and going water skiing that would be a different situation. Have a great vaca and give a call to ur Dr.