Technology

3DFINS Dimple & Channel Technology

To start we’ve found this video which explains exactly how dimples work on a golf ball.  So what’s this got to do with fins?  A bit trippy to get your head around, but in scientific terms, the physics behind air and water flow are the same.  So, how dimples work is the same for both golf balls and fins.

 

 

Full Techie Talk

As we all know, a golf ball with dimples will fly further than a golf ball without. What most of us don’t know is why? There are two main reasons:

  • The Dimpled Surface reduces drag.
  • The Dimpled Surface improves lift.

A lesson in Hydrodynamics

There are two types of flow around an object: laminar and turbulent. Laminar flow has less drag, but it is also prone to a phenomenon called “separation.” Once separation of a laminar boundary layer occurs, drag rises dramatically because of eddies that form in the gap. Turbulent flow has more drag initially but also better adhesion, and therefore is less prone to separation. Therefore, if the shape of an object is such that separation occurs easily, it is better to create a turbulent boundary layer in order to increase adhesion and reduce eddies (which means a significant reduction in drag) Dimples on golf balls create a turbulent boundary layer.

So we at 3DFINS decided to test these principles and apply them to a surfboard fin. With advanced Computer Fluid Dynamic testing, we compared two identical fins: the 3DFINS dimpled fin and the exact same fin without dimples. The tests were conducted by fluid dynamics expert Darren Stephens (formally of CSIRO) and the results were surprising. A surfboard fin with a smooth surface is much like a golf ball with a smooth surface, it has a lamina flow over the surface. This works quite well when going straight and at lower speeds, but when you start to turn and reach higher speeds the fluid starts to separate from the foil or fins surface.

A surfboard fin with dimples creates a turbulent flow. Turbulent flow has more adhesion so when you start to turn, the dimpled fin surface delays the flow separation, reducing the separation bubble allowing the foil to maintain performance. When the surfer is turning at high speeds, the turbulent boundary layer helps the flow overcome an adverse pressure gradient and allows the fin to remain attached to the surface longer than it would otherwise. This reduces drag, increases lift and improves overall performance of the fin design.

NEW INNOVATION "FIN TIP" CHANNELS:

It's been long known in surfboard design that Channels make a board go faster especially in clean conditions and down the line. But what has been unknown is the effect that channels have on fins. For 2 years 3DFINS designer has tested Channels of all shapes and sizes on fins, the results have been surprising. Channels irrigate the flow or help to direct the flow. This results in the flow passing along the channelled surface gaining speed and increasing pressure. The channels also have an effect of improving release when the flow is passing across the channels rather than through. The Channels break surface tension as the flow passes cross the channelled surface.

 3DFINS Computer flow dynamic tests are currently in construction stage we will release results in the coming months.