ChazInMT -- Well, credit where due then.
HydroJim -- I'm not prepared to defend the chart, I just posted it so I wouldn't have to go back through the thread. I think its t/c is the inverse of fineness ratio. But now I've re-read the first 4 pages; relevant post include:
The discussion seems to focus on NACA 6-series foils, and Clark-Y.
cautions against using airfoil data when the pumpkin seed is the real optimum. Excessive length increases skin friction, but that's a small percentage of the total so it's fairly 'safe'.