"Boat 7 was contracted because we need at least seven."
The 1997 SDR wanted 10, this was cut to 8 and at one point it looked as if they might only build 5 - but (thank God) #6 and #7 were ordered, partly to keep the yard open as per Boffin's post.
The biggest problem is how are they going to recreate the fabulous weather of Barrow in Adelaide?