When Paul goes for a ride with his friend Harold (Hugh Marlowe), they're shown having a conversation while sitting right next to each other. But both before and after that segment, they're seated normally apart as a driver and passenger would be in a vehicle.
It is impractical to switch on a boat's autopilot in a river of only a few chain's in width due to the closeness of the shore. Autopilot is typically only used in open water.
At about 35:48, right after Paul Sampson's remark about his needing to get used to wearing a leash, he turns to leave. Black tapes are then visible on the carpet for two actors hitting their marks, in the place where he stood.