Here is a numerical design tool which is really helpful for designing hydrofoils. This Excel spreadsheet was created by Zach Hoisington, a senior aircraft/aerodynamics engineer.
With this tool you can adjust speed, weight, wing size, motor pod size etc. Not only does this tool calculate total drag, it gives you a break down of where the drag is coming from to help you know where to focus your drag reduction efforts.
You can even estimate the stall speed of your design. The design tool calculates the required Cl for a particular design/weight and speed. By gradually reducing speed you will see a point Where Cl is above 1.00 and begins to climb very fast…the approximate stall speed.
The example below is my current design which I optimized for minimum drag at 15 mph. For optimized (minimum drag) at higher speeds, shorter wing spans are better.
Once we have more data from actual foils, it would be great to compare real world numbers to the predictions given by this spread sheet.
Here is the dropbox link for this spread sheet: https://www.dropbox.com/s/pf32dhyy7i1yovz/Hydrofoil%20medium%20AR.xls?dl=0
Example of my current design at 15 mph.