As far as I've understood, they sleep naps no more then 15 minutes without a pause.
Especially in areas where there is a lot of seatraffic and in times with difficult weathersituations the number of naps will decrease.

On the long run, on the wide big oceans, they take longer and more naps if the situation allows that.

Sleep-deprivation is a well known problem in these races.

But it remains racesailing..... Always at maximum speed, at the edge.