I radiused my Great Auk deck. I had laid out the offsets on a CAD program (I just posted the radius numbers on the Design bullentin board). I'm not sure how it would relate to the specific kayak designs you're looking at, but ... The rear deck is still almost flat very high radius curves. So there ellipse or radius won't make much difference. But on the foredeck I got a nice curved deck that is kept within the profile of the original design (no added windage). I think an ellipse would give you a nice curve, more interior room and the center line would be almost flat. A parabola that flat would probably not look much different to a simple radius. If it's a narrow deck-it might be really cool.
To determine the radius I used the old geometry proof "Any three points lie on or define a circle" My CAD Vectorworks (MAC OS) has it has one of its circle methods. I used the two shears and the peak at the centerline for the three points. I like the curved deck it gave me, its Fair and there were no stripping problems. If I was less lazy and less embarrassed by my strip job I'd post some photos.
If you don't CAD you can simply draw a line between your centerline point and your shear, bi-sect the line with a perpendicular line. Where it crosses the centerline will be the center of your radius.

Will

: Hi All, I am planning to strip the deck of a oneocean Cirrus and maybe a
: Cormorant. My question is; What is the best profile for a deck. radius,
: ellipse or parabola? A radius is easiest but I was thinking that an
: ellipse might keep the deck hieght down whilst maintaing room for feet.
: Also, how much extra weight could I expect to add by using pine instead of
: WRC for the stripping.
: Cheers.