And I'm guessing that the ship was most likely running at a reduced speed, as is often the standard procedure while in inland waterways (steamship companies don't like to be sued by waterfront property owners for washed-out bulkheads and damaged docks and vessels). A huge underwater mass like that is going to displace a LOT of water volume .....sounds like a memory to be retold for generations around the campfire :-)
I've enjoyed many a wild ride on the family sailboat when the Trident submarines pass by :-)
I beleive I may still have photos of that day and ship. My Dad darn near killed us all on several occasions on the wakes of ships. Many good memories of being in Panama.