The size of the portholes is dictated by the construction rules the ship was built under, as a cabin has to meet certain minimum requirements for space/lighting (including natural light) / ventilation/equipment level etc.
Pre aircon days this usually resulted in opening portholes, and as an 'emergency escape' were required to fit a mans shoulders.....
Todays constructions typically do not have opening ports.... all double glazed for comfort (until the AC breaks then you all sweat like a pig as you can't get airflow around a modern ship other than mechanically!! Mondern 'windows' are also typically rectangular, unless in the hull where physics/metallurgy dictate and round ports occur.
if you are a Captain and have a caring owner....
then you might get large picture windows. As a messman on a ship built cheaply in china...... you'll probably get one/two 12/14" half submerged ports....but as you're working 29 hours a day, who cares??