XTR Double Wing Quad
The 4 fin placement is crucial as the water flowing between the fins is like a fuel injector.
The advantage over a thruster is that a quad doesn't have a fin stuck in the center of the tail, and it makes it turn quicker and goes faster.
With two fins on the rail, you have more holding power for bigger waves. With two unique wings it gives this quad a large range in wave size.
The bottom is a single to double concave with vee on the tail with low rocker. Joe Blair is a pioneer in quads. He has been shaping and refining this model for the last 25 years.