I said 'inertial' when I meant 'stationary'. If the boat were co-rotating (thus 1000 mph) relative to pole, Einstein predicted time dilation (and without gravity, he would be right). If the boat reached the equator without friction, moving 1000 mph relative to surface, it would be stationary relative to pole, with no time dilation predicted.But Einstein did predict time dilation for exactly the situation of the pole versus corotating equator. I believe there is none at (idealised) sea level. Note that I have no interest in the time dilation of the boat before it is bounced in the right direction, and the point of bouncing it is to get it in the right state without doing work.