Hawaiian PhD Cliff Kapono brought to the forefront a study published in 2009 by Prasad Gudimetla, Neil Kelson and Billy El-Atm of the University of Queensland that confirms the popular belief that a quad will work better in large and powerful waves and a tri fin or thruster in smaller and weaker waves.

As Kapono points out in the study transcript, tests were done with two similar boards, the side fins being the same and with the same inclination, which were then complemented with a quad model and another with three fins.

From an incline of 26 degrees, the thrusters lost traction, and the quads did so from 37 degrees.

But explained in Kapono's terms, what was found was the following:

“Simulations were performed in ANSYS CFX with angles of attack ranging from 0° to 45°, allowing researchers to observe the response of each configuration as the fins were progressively tilted into the water flow. The results showed realistic hydrodynamic behavior with tip vortices and surface pressure gradients consistent with airfoil theory.

As the angle of attack increased, the lift coefficient grew linearly until stall, the point at which the water flow separated from the fin surface and lift decreased rapidly. The thruster reached its maximum lift (Cᴸ ≈ 0,93) at 26°, while the quad reached a slightly higher value (Cᴸ ≈ 0,95) at 37°, meaning that the three-finned thruster generated more lift up to approximately 30°, and the four-finned thruster produced more lift beyond that range.

Drag increased exponentially with the angle, showing minimal difference below 30°, but greater drag for the quadcopter above that point. When comparing efficiency using the lift-to-drag ratio, the propeller peaked at 7° and the quadcopter at 10°, with the propeller being approximately 29% more efficient at small angles and the quadcopter approximately 4% more efficient at larger angles.

The authors concluded that the three-fin configuration works best at low to moderate angles, providing greater maneuverability, while the four-fin configuration works more efficiently at higher angles, offering better stability and control at high speeds, such as in large wave or towed conditions.”

This confirms the increasingly common belief that quads perform better in powerful waves and thrusters in less powerful waves.

Below is the video:

 

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