The "fan boat on a river" question

[tw]

Originally Posted by Spexxvet

If you were driving a fan boat, whose maximum speed was 100mph, up river, and the river was flowing at 100mph, would the fan boat take off.... I mean move forward in relation to the banks of said river?

Exact same answer as it the airplane on a treadmill IF airboat has no drag and air is not moving (relative to river bank). At 100 MPH, water excerts drag even on an airboat. Therefore airboat will do something less than 100 MPH in relation to air and river bank.

Now if airboat was going downriver, then airboat would do 100 MPH relative to air and river bank because water (moving at same velocity which means same speed and same direction) exerts no drag on the boat.