When we first cruised on the Navigator (I think it was our TA cruise in 2009) the evening meal at what was then Portofino (since renamed la Veranda) was by reservation only. You made those with Paulo, the Maître d'hôtel, not on the website prior to sailing. We ate there once and didn't like it.

Since then there have been lots of comments, especially recently, about how lovely the evening dining at la Veranda is - across the fleet. it seems that "Sette Mari" will start 12th June this year but while the comment "reservations required" is there, it is not clear if these are made prior to sailing or once on board.