I have created a basic paddle design file here which you can download and modify to your liking.
Here's a bit about how to work with the file:
- You need Adobe Illustrator to open it.
- You can change the measurements to inches if you want by pressing Document Format in the top.
- You modify the left side and your modifications will be mirrored to the right side. Use the white arrow to select anchor points and move them around to change shape. If you are new to Illustrator/vector graphics I suggest you follow some getting started guide.
- There is a ruler tool, in the menu to the left. It helps a lot to get the measurements right for the shaft and blade.
- You can print the whole paddle and tape the papers together to get a good real size template. Choose "Pages side by side" when you print, otherwise you only get part of the paddle printed.
With some modification this method can be used for asymetrical paddles too. For example my upcoming paddle:
I hope this was of some help. And if you know any better software for paddle designing please let me know!