Your size is not an impediment for the Charles. The fireworks barges are longer and wider. Your first obstacle will be the North Washington Street Bridge. It is fixed and you may have to lower your antenna at high tide - don't ask me how I know. Traffic lights will direct you into one of three locks which are immediately behind the bridge. All have ropes hanging down to use for holding the boat in place. You'll be directed by the lock personell when to go. The two smaller locks have fendered floats at water level-rig your fenders for the waterline. If there is a lot of boating traffic, they will open the commercial lock. You'll need fenders on the gun'l. You will also need able bodies individuals to hold the boat in place as the lock fills or empties, depending upon the tide.
Then there is the railroad bridge which the operator will open if there is no train scheduled. Doesn't matter if the train is on time or late. He won't open until it passes.
Then there is the Craiggy (sp?) draw bridge. He won't answer the radio and sometimes falls asleep, so you may need to wake him up with the proper horn signal. Again traffic light controlled.
Lastly is the Longellow (Salt and Pepper Shaker) Bridge, just before the Hatch Shell. When you see it you'll know why. Keep in the center span and you will clear with better that 40 feet, although it does look like it.
Don't even try to enter the river close to morning or evening rush hours. The train bridge and draw bridge won't open.
After all that, it is not complicated at all and usually is a pleasant experience. Just takes time and patience.
Don't be misled by the depth of the water. The bottom is muck on top of hard pan. Most anchors won't dig in very well and hold by shear weight.
Gene