The two people in the small boat are capturing the cables from the cargo ship to be connected to the trains on the either side, called "mules". You can see on upper right 1/3rd below the top.
![Image](https://farm8.staticflickr.com/7846/33049882788_94d08c1e4f_b.jpg)
Ship entering the lock.
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![Image](https://farm5.staticflickr.com/4865/46200471974_3c9315aa54_b.jpg)
You can see the mule in action. There are typically 4 of them that maintain the ship in the middle by keeping the cables taut as the ship moves forward. Very tight fit. There is a new canal to the left that is wider and ships that fit that canal are called Panamax. Currently that is the widest a ship can be, to able traverse the canal.
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![Image](https://farm8.staticflickr.com/7903/46200479544_c85ea4156a_b.jpg)