Thats not really the same style fin Greenough and Thomson made, but its possible Greenough may have seen that fin and drew some inspiration from it? Who knows...
To my understanding the hatchet style fin that led to the powerdrive fin was invented by Greenough for his knee board, and then once he traveled to Australia and met Mark Thomson, they collaborated together and Mark was the one that modified/adapted the hatchet style fin for shortboard and that is how the powerdrive fins are credited to Mark Thomson. It was Mark that first adapted and used those types of fins on a shortboard.
Its actually been pointed out here on this forum that the picture featured on the bottom of the True Ames website is Mark Thomsons personal surfboard with a tri-fin powerdrive fin setup. It appears that Mark Thomson made the board in the photo himself, and made and glassed those fins himself. The True Ames website is using the photo (i believe without his permission) and claiming it as their own creation. If I was Mark Thomson i would demand that Chuck Ames remove the picture and/or the correct the storyline on the website. The True Ames website doesnt mention Mark at all and actually credits Chuck Ames as the one that used Greenough's fin as a thruster design on a shortboard and then shows Marks board.
The whole blog section storyline on True Ames website re the hatchet fin seem to be inaccurate.
It would be interesting to hear what Chuck Ames has to say about it.
Correction: Here is the website URL.
Above: a photo of some of George Greenough's original designs for the paddle fin, and a collection of some windsurf boards and molds. ( Spoon and Chopper ) He used to make almost all of his fins, boards and other equipment, and was an innovator who enjoyed creating and reinventing. Here is a...
www.trueames.com