The main clue goes all the way around the board from 1a to 1a.
I thought this would be an interesting way to do a puzzle. The main clue is 17 letters and goes around the entire board, with the clues in the middle filling in the blanks.
Really clever construction, fun to solve. If you're interested, there's a great book about the construction of the Canal. it's called "The Path Between the Seas," by the historian David McCullough. (Sorry, I'm a real book nerd and I'm one of those weird types who finds history fascinating.)