Poor poor Petrie, he really has to carry a burden; and poor poor Ducky in case he doesn't make it anymore
I love that picture Sky

including the expression of Petrie (an alternative idea would have been to have him clench his teeth with effort, but I think the face as it is is working out very well). I also really like the fact that you don't have Ducky just "hanging around" passively but she is really visibly enjoying that ride pointing at something she has apparently spotted.
As for criticism, I think the fold between Petrie's upper- and his lower torso may run a bit too deep, especially when it might be smoothed out a bit by the weight that is pulling Petrie down while he is trying to pull Ducky up.
It is kind of funny that you come up with this picture right now for just yesterday I thought of a scene for an LBT story which involves Petrie carrying Ducky. That scene however is more of an emergence, Petrie works out more like a parachute, and the landing will be a very rough one.