Or a trebuchet?
Now you’re talkin… 
Yeah, but you’d need two trebuchets–one on each side of the river…
I agree with those saying “I have no idea, but it sounds really fucking cool.” FWIW.
Or some kind of pendulum set up at the midpoint.
Don’t forget to factor in the cost of eels.
“Boat (n): A hole in the water one throws money into.” Just parking (er, mooring?) a boat is expensive; actually going anywhere requires money and/or dedication.
Reminds me of a song…
“My hovercraft is full of eels.”
Nametag has it right; owning and operating a boat is prohibitively expensive unless you have money to burn or have profitable gain from the boat.
Stranger
No, not any more at least. I’ve lived on it my whole life, and have never seen it freeze. However, I have photo of a once plowed ice road from Stonington Point Connecticut to Fisher’s Island, New York [10 miles north of Montauk]. It would freeze from December through April and people would rive their model T’s out to Fisher’s Island to - get this - hunt seals.
I’ve known several people who live on island in Long Island Sound who commute by boat. One man has been doing it from mouse island for decades. I see no problem with it at all…except maybe fuel cost.