This is a current thread on Surfer .
I posted this :
I think it’s been well established that down rails promote water release thereby resulting in less wrapping of water over the board as one expects with 50/50 rails. Regardless, I’d defer to your judgement on that before relying on what’s been said before.
Stretch wrote this :
"How bout if i answer. This is hydrodynamics 101. As water flows over a curved surface, velocity must increase. creating a vacuum ie suction. So soft rails engage more than sharp rails. with the new high lift bottoms 50-50 rails are a big advantage. i think my track record speaks for it self. "
There is a trend to use round rails without what one shaper calls “parts” . It was fun hearing that because that is how I look at rail design , a combination of “parts” . 
" As water flows over a surface , velocity must increase. creating a vacuum ie suction ". I do not believe that statement is correct , but if I am wrong I am sure someone will correct me .
OOPS sorry , "curved surface ".
Mr Griffin,
I suspect you know the answer and hope you enlighten us.
I view rail profile as a leading edge of a foil, like a fin front edge. I try to get my rails to generate lift when on edge. I don’t want lift in the tail, and if the nose rail is buried then something’s wrong.
I pull thickness forward so that the entire buried rail is a foil front to rear as well as a foil bottom to top.
If my board’s in trim, then small undertucks and edges prevent sinking, rather than rail shape per se.
Does it work? Who knows. It’s my mental model that guides design decsions.
PS I’d like to see that profile picture with tangents (the software option that shows those lines that stick out to show you how fast the curve is changing).
If I may
I’m a surfer first.
And while all you engineers were studying, well, I was testing.
Also I am an “Olphart” and regarding rail shape, I have seen a lot come and go.
But I have never forgotten anything I have “fondled” or better yet surfed.
Rails, rails.
Longboard days 50/50 was the norm and had a function.
With Edwards, Iggy and other “performance guys “knife” rails ruled.
Of which were meant for Rincon, El Cap, waves of energy, yeah.
My drift?
And Hell I’ll say it!
Rails, it all depends
And that is why you really should have a quiver.
That said.
I don’t listen all time
but when I do
I listen to Greg.
A flat bottom with tucked edge can do an awful lot!
I went thru the whole change .
Reading claims I know are from someone who did not exsperience these changes is fun .
This rail shape can be modified a lot but still has 4 parts to it .
The current round rails are being ripped on by the best - thats all that counts today .
I will keep making what I have made thru all this
Here is my post from that thread:
“Edges release, curves grab.”
That said, IMO there is no one “right” way. Different shapers get different or similar feels to other shapers based on combinations of board characteristics. Rocker, rails, bottom contour, foil, etc, etc, etc. all play off eachother.
There are best design concepts .
Alter them to your desired personal taste .
Is it true “edge releases, curves grab”? So if it applies to tails a swallow releases more than square? Makes sense. I guess the rail design will depend on the type of waves and objective of the surfer.
Tucked edge for maximum plane - Then what I call the lobe , the curve from there to the apex for control “suction” - then the “Wall” breaking slightly inward from that curve to break away release from that suction , angling inward to the crown of the rail then into the deck crown .
All these “parts” can be modified any way you desire .
Swallow tail was created to reduce area to keep the tail down on the water before tail rocker was added .
(1) Yes, it’s true.
(2) And, the Tooth Fairy is real. (Psssst, squaretails release best.)
Hi Greg Griffin do you use the tucked edge on your latest longboards? Only I saw a guy at the beach today with one of your old T and C longboards and noticed it didn’t have the tucked edge nose to tail just in the rear quarter ish.
I made what T&C wanted , that included soft rails .
When I worked for Russ K . Makaha in the 90’s I made them all with my tucked edge , Dino Miranda winning his world Championship in 1998 on one . :-)
Great post. Thanks.
Care to share some numbers on tucked edge?
I pull about 1/8" undertuck in nose to 7/16" undertuck at centre to zero in the tail using the outline template to connect he dots.