JD-EE:
I don't see where you accounted for either the spreading loss of the signal or the noise summed over the whole detection filter band (at least 100Hz). Remember that the noise figures I quoted are 1/sqrt(Hz). I refer you back to my original post on this topic (in fact, my first post on this forum):
http://www.pprune.org/5683946-post951.html
Given that Urick lists the noise at 37kHz, deep, as being between 18 and 42db re 1uPa/sqrt(Hz) for sea-states 0-6, I may have picked a little too much noise for my example, at 37db, but no less than 33db would be the right number. I don't think the 18db conditions are common; even sea-state 1 brings the noise to 25db.
Note also, in the case of the submarine (assuming, as I do, that it did not tow a deep array), that it is in shallower water, where its local noise may be a somewhat higher. Urick, first ed., shows little change in amplitude unless within a few hundred meters of the surface, but the only data are for 3kHz and below, so I don't know about 37kHz.