The nose equation is simple — circular geometry — the ellipse. I use variations of the ellpse in SB design elsewhere also.
The tail curves are a variant of my master equation (the master equation/curve is my secret sauce). I use variations of that equation in several areas of SB design. I engineered the master curve from a significantly more complex equation. The tail curves are polynomial.
Regarding the Coanda Channel, it is not in this E-Type Retro. The bottom is flat nose to tail. I really liked the outline of this template. When nobody would CNC shape my Finless Fish (Coanda Channel in the tail), I decided to have @MRat make me a quality Retro Fish using my Finless Fish outline/template. The “E” in E-Type stands for Equation/Ellipse.
The Coanda Channel in the Finless Fish design can be viewed at these links,