Posted November 29th, 2017, 06:18 AM
Passenger space ratios can give a rough idea of how "spacious" a ship is, but it must be considered a very rough estimate. For instance, basing it on double occupancy, can skew a ratio if one ship has more 3rd/4th berths than another, and typically sails with those berths filled. Another problem with the ratios is that it uses "gross tonnage" which includes the volume of tankage, machinery spaces, and crew spaces. If the pax/crew ratio is different between ships this can skew the pax space ratio because of differences in the amount of crew spaces. Likewise, as ship like the QM2, which has an enormous power plant in order to provide the top speed she has, most likely takes up a greater percentage of gross tonnage in machinery space and fuel tanks than a smaller ship like the Viking Star.
Gross tonnage is used because it is a readily available figure for sites like Cruisemapper to get, but using "net tonnage" would be far more accurate. Net tonnage is the volume of "revenue generating spaces", meaning passenger spaces, discounting the machinery, tanks, and crew spaces.