If you look at the rope it's attached at the door on the left hand side of the helicopter. When he starts to tow the boat forward this would cause the helicopter to twist to one side and ultimately crash. (The Centre of Gravity is being moved towards where the rope is attached and may actually put the new CoG out of limits)
The helicopters you see lifting or towing stuff would probably be attached to a harness on the underside of the helicopter at or close to the CoG, this would make lifting and towing possible. The lifting point is pretty much directly below the main rotor shaft and any weight added anywhere other than this lifting point will change the CoG.