Contact Rishworth for example rosters and all the contract details for all the different bases. That's what they're for and they reply very quick.
The improved OSM contract after the initial 3 year contract seems to be a big secret though...
-Only 10 days off guaranteed. Given in blocks of 5+5 or 4+4+2 or random.
-Mostly W-patterns: From A to B to C to D to A.
-Some stand-by days to fill the gaps. Could be at home base or could be in a hotel somewhere else.