If you are staying at the BC, you can catch a boat at the YC Boat Dock to Epcot and Disney Studios. However, you can probably walk more quickly to Epcot from the BC than ride the boat.
The only way to ride a boat to the MK from BC is to walk through Epcot, catch the monorail to the Trans and Ticket Center, get off the monorail and take the boat over from the TTC to the MK. Or take the bus from the BC to MK directly.
No boats to AK from anywhere.
If you are staying at POR or POFQ (one boat) or SSR or OKW (another boat), you can take a boat to DTD.