Not that any Catholic who has ever taken an ocean cruise ever has to worry again, thanks to the clarity that Pope John Paul II provided in the motu proprio Stella maris
. Here are the relevant excerpts, all from Section 2.
II. 1. In this document, the terms used are defined as follows:
a) Seafarers are those actually on board merchant ships or fishing vessels, and all who for whatever reason have undertaken a voyage by ship;...
(emphasis and bolface of roman numeral in original; remaining bolface added)
III. Mindful of the special circumstances of the people of the sea and taking into account the privileges which over the years the Apostolic See has granted this people, the following is established:
...2. [/b]Seafarers are not bound by the laws of fast and abstinence[/b] prescribed in can. 1251; they are advised, however, when taking advantage of this dispensation, to undertake a comparable work of piety in place of abstinence, and, as far as possible, to observe both laws on Good Friday in memory of the sufferings and death of Jesus Christ;
(boldface of roman numeral in original; remaining boldface added)
So, according to the late pope, anybody who has ever taken a cruise vacation is a "seafarer" and thus not bound by the laws of fast and abstinance. Further, a motu proprio
(literally, "on my own" meaning that the pope issued the document on his own initiative rather than at somebody else's request) is capable of establishing new law or derogating from existing law in its own right, and thus becomes the governing law by its promulgation.