Using the water taxi, with the engines split might not have the desired effect due to the distance apart of the two engines not producing enough torque. Large ships, eg container, ferry etc have the engines far apart, which produces large amounts of torque, even the pilot boats have a couple of feet between them, the taxi may not.
Ok just tried it in the game - the starboard shaft/jet doesn't work at all, which to me suggests that infact it is a bug - of that the Taxi is single engineed? I've tried running her up the beach but can't see the hull.
Steve