My 'normal' pattern these days is around 6 hours (midnight to 06:00), that I think is a result of growing older and primarily having a 9 month old. In my 20's I'd regularly manage on 4 hours sleep or less and even today can survive on that for a few days.
However my sleep goes to hell during bouts of depression, i.e. the anxiety, thought patterns, and at times outright panic associated with them prevent sleep, the best I can hope for is simply laying in bed with my eyes shut so my body physically rests (and so I don't freak out my wife by wandering off in a highly agitated state in the middle of the night). The worst I think was 5 days with a combined total of 6 hours sleep, and that was medically induced. By the end I was hallucinating.
I have tried ployphasic sleeping but only in the 4,4,4 yacht crew example given and then only for single overnight passages. To be honest for a single night I found it easier just to stay up all night as long as I knew there was down time available the following day.