A type of SU Ursae Majoris star with a very short interval (20–50 days) between superoutbursts, i.e. outbursts that are about 2 magnitudes brighter and five times longer than normal outbursts. Such stars typically spend a third to half of their time in superoutburst, with a rapid succession of normal outbursts (typically about one every 4 days) in between. The mass transfer rate is nearly ten times that in a typical SU Ursae Majoris star.