Enough people to establish viable genetic variety and allow for some attrition by accident but not orders of magnitude more. A minimum of five initial languages and a maximum of dozens -- we can tweak this somewhat. Emergency instructions might well have been given in more than one language (I'm guessing English, Spanish and Chinese.) The boat was at least 1 year but less than 10 -- it takes months to do the trip "now", and tech has progressed.

All this happened at least a couple of hundred years ago, so whatever process began then has had plenty of time to progress further since; I just don't want to establish a situation that could not logically arise from what would have been the initial facts on the ground.