As the length of the racing course is limited, large regattas are organised into "divisions" of 12 to 20 boats. Each division races separately, but they are ranked to achieve an overall order of crews: e.g. the top crew in the second division is considered to be one place behind the last crew in the first division. The first day's starting position is based on the final positions from the previous year, though in the bottom divisions the boats may be placed according to qualifying "getting/rowing on" races held before the event. This allows boat clubs to introduce new crews. On each day of a bumps regatta the division races are rowed in reverse order, i.e. the lowest division first. A crew finishing at the top of a division race goes on to compete in the next-higher division later that day (starting last). Alternatively, a crew finishing last in a division must race in the next-lower division the following day (starting first). This is referred to as a "sandwich boat" and allows crews to move between divisions.