A little bit more reading suggests WIFI solutions are overtaking GSM solutions on cruise ships these days. Read this article from last year:
http://www.forbes.com/sites/marcwebe...ip-passengers/
No mention in there about data, just about voice calls. However they seem to suggest conventional VOIP does not work very well due to lags. Voice calls need to be made via a special app like
https://play.google.com/store/apps/d....softphone.mtn
which I presume allows you to authenticate on these WIFI networks as well as adding some extra technology in order to enhance voice quality.
Also read:
https://www.connectatsea.com