This paddle blade is designed to create extra drag and more resistance due to its concave shape on both sides.  In theory, it should be able to “trap” more water by using extra surface on both sides, helping it stay in the same spot, increasing the performance.

It is approximately 21' long and 10' wide.  Fits Zodiac's 35mm paddle shaft, but could work with many other brands.  Please leave requests for variations in the comments, it's very easy to modify this design.

Printing

Infill of around 10% should be sufficient.  Can be printed either as one part, or in three parts and then glued together.  It might be beneficial to print by laying the part(s) flat, in order to increase latitudinal strength and ensure the compartments created by the infill pattern are as small as possible.  Needs to be reinforced with fibers and then painted.