The 12 ft skiff is an interesting thread. The CFD work that has been done is the sort of thing that only AC teams would have had access to a few years back.
The 12 ft skiff has no hull rules so the rails are not a rules dodge.
The 12 ft skiff and the UK Cherub are developing from the flat planing shapes to more like high speed displacement hulls that will plane. The rails can help in increasing lift from a rounded hull - they kind of act like end plates. They also act to release spray as you suggested. On the 12 ft skiff, one important role is that they add pitch damping - the rig height and fixed sprit make the 12 ft skiff prone to pitching.
I did consider spray rails on the E6 - the inside of the rail was at the chine measurement so it was not a rule dodge. I wanted to keep the rails above the static waterplane so they didn't add drag when sailing upright. I did quite a lot of CFD analysis. Unlike the findings reported on the 12ft skiff site, I couldn't get any improvement of lift to drag. It appeared to be better just to use conventional chines but at a lower deadrise.
The T foil gives the Cherub a huge advantage over the 12 ft skiff. Moths are now about 2 knts faster upwind and around 3-5kts faster downwind than they were maybe 4 years ago. This speed increment has come from foil development. I suspect there is still a lot more performance to come from the
development of foils on the Cherub.
