BIG SUN HULL: HYDRODYNAMIC VS AERODYNAMIC RAIL DESIGN


 

When was the last design development in the log? Maybe over 50 years when Nat Young foiled the hell out of his 9'4 in 1966'  and added a 10' inch upright Greenough and called it 'Magic Sam'?

Bob Simmons is widely credited as applying his knowledge as an aircraft engineer to surfboard design to give us features like concaves, kicked noses, aspect ratios, optimum weight and rail shapes. This happened in the early 50's. 

But we ask... when it comes to rail design in logs, is it correct to apply aerodynamics to a surfboard which is.... hydrodynamic.  

Modern surfboard design talks about planing speed and lift, the idea being sold that once we generate enough speed we fly. We put it to you, is lift really what a log needs? Theorize that lift is actually an effect of drag. Drag causes an aeroplane wing to lift. Aerodynamic shapes are calibrated to ideal planing speeds and below the correct speed the thing drops out of the sky, and above the correct speed turbulence is generated and the thing... self destructs. The truth is, that on a log, the spectrum of speed we are dealing in, is low. Enter the displacement hull. 

A displacement hull is different to a planing hull. A planing hull needs to hit a specific speed to start working (think your modern high performance board and why it needs a good wave to get going). A planing hull in fact 'planes' above the water, where a displacement hull moves through the water. A displacement hull's ideal speed spectrum is from nothing, up to when speed forces it out of the water (in the case of a surfboard, but an interesting phonomenum is that a true displacement hull will actually get sucked into the water at higher speeds and fail that way.) This is why logs are so efficient in small waves. Small waves don't go fast enough to pop boards out of the water, they push boards through the water. If you follow that a log is a kind of displacement hull, then continue with us into our next question. Why are log rails aerodynamic in nature instead of hydrodynamic?

We theorize to increase the speed of a log one would need to raise the fail speed, i.e the speed at which the board wants to start planing. To do this we have raised the entire rail line from 50/50 to 95/5. 

The first step in development was to implement a raised rail in the nose and tail in all our big board models to good results. It seems contradictory to say that the raised rail details have increased stability along with maneuverability, but that is what we are finding. The progress made us want to push further.

Introducing the raised rail hull. The raised rail results in a nice rolled hull and a completely flat deck. We look forward to getting this in the water and letting you know the results. We have no idea how it is going to go but that is half the intrigue. if you have any ideas or opinions, or just want to chat feel free to contact us to discuss. We love talking boards. 


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