Thoughts on the word "fathom"

Why do you think Hemingway used to word fathom so many times. We know one of the meanings relates to marine fishing as a form of measurement, but I believe that Hemingway uses the other definitions of fathom to his advantage. Fathom also means to comprehend or understand something. What I don't know right now is what did he mean by using fathom besides as a measurement? Did he want the readers to understand something hidden in the text? Or is there something to come up that he wants us to look out for?