BigQ wrote:
Small diesel locomotives that ferry ships through the Panama canal. Two at front of ship, two at back of the ship. They don't pull the ship along, but keep it centered through the locks. Ships use their own power. Amazing to see them climb hills, using the cogs in the center of the tracks.
Here are a few photographs I made in the Panama Canal in 2015 (old locks) showing the donkeys and turntables.