"Dimple" fin.....

Opinions please? It supposedly works on golf balls. Bill Thrailkill was working on a textured surface. Does this disrupt ‘laminar flow’ and if so, is that a good thing? Is this like the old controversy regarding smooth shiny gloss vs sanded finish? Gimmick principle? Actual experience with this sort of idea welcomed.

ask the willis brothers.

I have seen advertisements on products saying “ribbed for her pleasure” though

From what I remember of previous discussion here, the golf ball thing only works because the mall spins. Not translatable to continuous laminar flow. I’m too lazy to search the archives.

All the best

I think Bernie has a set of fins with dimples. He has everything different and weird. I have his McCoy gull fins I’ve been wanting to give them a try, but haven’t yet.

The dimples would probably make the fin stiffer maybe less likely to snap , not sure if that is intended .

Pushing the laminar boundary layer further back at the range of surfboard speed would be easy to proved in a lab setting with this specific product. Shenanagins like this are outlawed in world class sailboat racing. Also selling this product might make label you as superhydrophobic which could ruin your career and reputation.

This was discussed several years ago.
Dimples work well for a small, dense/solid sphere traveling through the air.
My take on Hans’ explanation was that the dimples offer no significant advantage on a surfboard fin. As I recall, the effect is related to Reynolds numbers.
If I find the link to Hans’ old post, I will PM it to you.

My bad…

I found the thread - 5 years back and 199 posts. I somehow missed them all but upon review, found every one of them to be truly illuminating! Did anybody actually try one? Did the ‘hoax fin’ ever make it in to production and change surfing as we know it? Does the world champ ride them yet?

By adding texture or features like bumps /dimples, more surface area is gained within a given outline. But really, how much is gained? If the number was more than 50%, then it might be significant. I’m not seeing it in this fin however so it could be something else.

Flow along any surface is both turbulent and laminar, and comes in layers. Generally, the flow immediately against the surface due to friction is considered turbulent (slower) and as the friction diminishes away from the surface it becomes laminar (faster). The more friction at the surface the thicker the turbulent layer is, and the effective laminar flow decreases. So the dimples would make that surface flow slower. Overall it would seem to make the fin perform as if it were thicker in cross-section. In any case, the overall flow is definitely slower than a smooth fin so more drag.

I searched 3D fins about their “innovation” but found nothing with any technical meaning whatsoever. Only that a number of people tried it and said it gave them an edge in certain conditions. In golf balls, the technical justification is that dimples provide more lift aerodynamically; this would imply that as it spins the dimples create higher flow under the ball than the flow above it. A uniform sphere with uniform dimples that has a pressure difference top and bottom? That lift may be a gyroscopic / gravitational effect unique to spinning spheres where the dimples orient the spin axis which effects trajectory. This doesn’t translate to fins however so it’s not a valid analogy.

Perhaps it does work but it’s the size of the dimples that matter. Board Lady says a board sanded to 600 grit goes faster than a polished gloss board. Wouldn’t 600 grit look dimpled under magnification?

Hi Monk, I would expect a sanded board to mostly have scratches that are parallel to the length of the board, like micro channels instead of dimples.


Dimples & sand vs. gloss are two different things. Sand/gloss has to do with surface wetting & associated friction. Gross changes to a surface has a different effect, much thicker turbulent layer than 600 & gloss.

Also, regarding riblets or micro-channels:
“the optimum height of the riblets changes with speed, so any riblet choice is a compromise.”

its about a external boundry layer that adapts to changing pressure dynamics that nothing static can duplicate it. Channels, dimples and ridges only redirects water flow and doesn’t adapt to accomodate it.

Goes back to the study of a dolphin/porpoise skin and how it creates a dynamic boundry layer that changes shape to promote the most efficient and hydrodynamic waterflow based on the pressure gradient encountered. KInd of like that pilot’s face riding in the open cockpit of that rocker chair the porpoise’s external epidermal layer is very soft and porous and reduces the tension between the water and the animal which is like 80% pure muscle. Morey was envisioning something like this when he started playing around with softwater craft. I don’t remember of allot of this but I was deep into this stuff in the 70’s after reading Tom’s article in Surfer.

I think you need something biological like human skin or maybe like a half filled surfmat that constantly changes shape depending on need. That’s why they are so fast and why you constantly need to manipulate them.