The navigator is Jan-Luck Nélias and is not aboard the boat, it is part of the team but not part of the crew, or at least it seems to be that way. I cannot find the rules.
Strange, other teams have navigators onboard. Maybe rules were changed, but the article says "Then before the race, you can pay for data, so there are lots of different models we use, and lots of different contractors and consultants. I'll contract with people like Ken Campbell at Commanders' Weather, to be a professional consultant, and I'll pay for data from places like the ECMWF [European Centre for Medium-Range Weather Forecasts] model. But once the race starts, then you can only use free data that is publicly available to everybody."