We used to do 6 and 6 in this neck of the woods on an OSV but if we were running anchors we had an extra mate, 6 on the bridge, 6 on the back deck and 6 off. STCW kicked that into touch and with DP the normal is 2 in a watch working 12 and 12. When it was 6 on 6 off we always picked up another mate for a run job because the pacific is a pretty big back yard and if one watchkeeper was incapacitated you still had two.