Military ships and civilian ships have massively different crew needs. The
Daniel Morrell and the
Edmund Fitzgerald were both large Great Lakes bulk carriers, with the
Fitz running close to 40,000 tons loaded, and both carried crews of 29. A loaded
Liberty ship went about 14,000 tons, and had a crew varying from 38 to 62 (that is from Wikipedia, so I would like to check that more closely), while a WW2 US Navy Cleveland, with a full load displacement of about 14,000 tons had a crew of 1285.
The British, in World War 2, converted a number of bulk grain carriers and oil tankers into what were called
Merchant Aircraft Carriers, basically a cargo ship with a flight deck added and carrying 4 Swordfish aircraft. The crews, with air complement of about 40, total 107. Comparably sized purpose-built escort carriers had crews ranging from 555 to 700.
In World War 2, a British
Military-class armed trawler, with a coal-fired boiler, built to merchant standards and designed for post-war conversion to a fishing trawler, had a crew of 40. A very comparable US Navy PCE (Patrol Craft Escort), with a Diesel plant, had a crew of 110, but was built to warship standards.
The current US Coast Guard mandated manning standards are here:
http://www.uscg.mil/directives/listing_cim.asp?id=16000-16999
covered in Marine Safety Manual, Volume 3. Those are regarded as overly-generous by many other countries, but that is what a US-flagged ship
MUST have to operate.
If you want a better idea of what crew requirements are for current and older ships go here:
http://www.apolloduck.com/
Except for passenger-carrying cruise ships, you will discover that the crew sizes are about the same regardless of the size of the vessel, and that they are a lot less than military ships.
For sailing ships, the disparity between merchant and warships was even greater, with the crew of a sailing merchant ship being based on what was needed to manage the sails, and officer it. If traveling in a hazardous area, it might carry a few extra crew to help with manning whatever self defense guns were carried. A 400 ton, 3-masted whaling ship would carry a crew of about 37 to 40, with about half of them being required to man the whale boats. The 18-gun sloop of war I mentioned in an earlier post would be very comparable in displacement and sail plan, and required a crew of 140.