Hello John,
I personally have shot only a few times on livaboards, but IMHO here's a good chance to play with the audio a bit. A voiceover intercut with a dive briefing could be a nice idea.
Keep the gearing up sections short - as you have found out, this becomes repetitive. There are only so many ways to shoot that, so reserve each one for a separate day.
Checking the air is only one aspect of gearing up - make short shots of people getting into their equipment/suits and vary the angles (up,down). Use fast paced music and make it look like an action movie. Or put the shots in slo-mo in post - that produces a nice action effect as well.
Show some non-diving activities to break up the pace.
Keep it short in general ... who wants to sit through 2 hrs of video?
be creative
Sven