I don't think that I would take the charter boat into Savanah. I'm not sure TMM would want you there anyway.
The entrance is shallow and tricky.

Why not spend an extra day at Leverick? Rent a car and drive to Savanah, the Baths, Copper Mine, stop at Hog Heaven. Take the Saba Rock ferry for dinner...

Then hit Cooper on the 17th.

M&M