im not sure just how the laws are written but in my opinion the boat under power should always avoid a boat that is drifting. but that's just my opinion and what I do when trolling. but remember its better to give up the right of way than to hit another boat.

you wouldn't believe the boats that's out there that doesn't know the boat on your right has the right of way. but that all goes out the window when it comes to a sail boat under sail, then the sail boat has the right of way except when overtaking and passing a boat then the sail boat must give way to the boat being passed. but many times I have given the right of way to boats on my left when they just kept coming. its much better to use your head when trolling and give way rather than hitting the other boat or tangling lines with them even though you are in the right by law.