I could be wrong Mark, but that schematic looks to me to be some designers way of manufacturing a hull with "tumblehome" yet still make it from out of two "female" moulds (instead of out of two "split down the middle" halves). In so doing the "hull/deck" join becomes the "step" or high chine along the sides. Building a hull in "female" hull and deck moulds has always been much more economical and time conservative than "split moulding”.
Basically the hulls would be built "upside down"