The circle is where the Hilton Garden Inn is. The star is where the sober boat will be docked. If you’d like to walk as a group, you will meet Annie and Bill in the lobby at 3:10 with hopes of leaving at 3:15 or so. The boat will leave the dock at 3:30. 
The boat will only make one more trip back to the hotel side of the river at the end of the reception (11:15-11:30).
Directions:
Leave the hotel from the main entrance/exit. Walk straight toward Jefferson/N Summit St. Take a right on Jefferson and head straight toward the river until you run into the boat.