I was watching the island hoppers series and there was this old Aussie expat in St. Maarten in the Carribean shaping boards with dimples on the bottoms. I know dimples make golf balls fly farther but does anyone have any insight into how they effect the hydrodynamics of a surfboard. If anyone has pics please share them!!!
Willis Brothers in Hawaii used to do this on their “Phaser Bottom” boards back in the late 80’s-early 90’s.
There have been threads before on this. Search the archives and you’ll find them.
They energize the boundary layer but they increase the wetted area too. They may also aerate which may or may not have positive effects on performance. Also would seem to be a pain in the arse to glarse.
to summarize the argument as I remember. It reduces cavitation(maybe) dimples only really work when it is a sphere moving through a uniform medium(no water air combo) benifits are miniscule if at all. pain in the ass to glass.
Dimples = bullshit.
Look: every time you want to make water move or change direction, Newton’s Law says you have to input energy. So any disturbance on a bottom that otherwise follows a streamline, will cost you energy.
Dimples don’t “aerate” in any way shape or form unless there is already “air” there, in which case what’s the difference?
HOWEVER, they may induce turbulence, which in turn may reduce the drag of carrying “attached” water along with you. Prandtl’s seventh power law sound familiar? They could be conceived to reduce overall drag like the dimples on a golf ball, IFF you are operating in the same flow regime. Which I seriously doubt.
Oh, and yeah, dimples will be a royal PITA to laminate, hot coat, sand, finish coat and of course, to gloss and polish.
Pedantl’s Seveneth Power Law… no, but I said the exact same thing as your remark about inducing turbulence by saying “energize the boundary layer,” ya just missed it! More to the point, they didn’t put vortex generators on airplanes, which make the flow do something on the front end, because they made it LESS efficient on the back side.
Air occasionally gets under surfboard, don’t she? And if the pocket retains it, no? I’m not married to it, but there’s your aeration.
“” They could be conceived to reduce overall drag like the dimples on a golf ball, IFF you are operating in the same flow regime. Which I seriously doubt.“”"
for the bboard to behave and benifit like a golf ball it would have to moving at relativy the same scale speed os that the Reynolds forces would come into play…quick and dirty calculation suggests board speed at about 250 mph…hummmm, interesting
I have no idea what is going on with those Phasers under there as far as hydronamics go. I used to ride boards like this back in the day though, and I can tell you what they feel like: From memory (always a little dicey for me), my boards seemed a little looser and softer in the pocket but never quite as crisp. Like they never quite just broke free and ran.
I’m sure there is someone out there much smarter than me that can sum all of this up in the concise 15th law of hydronamics. In the mean time, I hope my vague recollections are of some use to you.
My memory of what a pain they are to glass and sand is perfectly clear.
It bears mentioning at this point: water’s density is about 800 times that of air–I don’t know what the saltwater part does to that in numbers. And there is no standing/dynamic water/air interaction or planing dynamic with a golfball either. Theyre just not the same thing overall, at all. So who knows?
I reckon if you ain’t ridden one, ya just don’t know. I don’t know. I bet you don’t know. Same goes for the Pederson “jet bottom.” How could you know? Hell bumblebees aren’t supposed to be able to fly.
Relevant research to this thread:
Its all about flow attachment, which is more an issue over surfaces that have very quick convex curves, i.e. a golf ball or sharks i guess. Artificially tripping (either by shark scales or dimples) a turbulent boundary layer allows flow to stay attached to over a convex curve better than if the boundary layer is laminar. As honolulu mentioned above, flow regime is also important here, certain phenomena happen at certain speeds, fluid densities, viscosities, etc. You cant assume that a surfboard or a fin is going be operating in the same flow regime as a golf ball, or a shark at 50mph. I dont really see where this idea of flow attachment would help performance of a surfboard anyway, except maybe improve fin stall angle?
look, dude, dimples are for shredders.
My cousin, an aeronautical engineer gave me an answer to the golf ball question: He said that the dimples in a golf ball work together with the spin of the ball to give it more lift. Since it stays in the air longer and somewhat higher, it flies further.
I don’t really know if any of that translates to surfboards.
BUT… haven’t most advances in surfboard design come from trial and error from creative foam herders who weren’t afraid to try something new? I say, Go ahead and try it. If it works great. If not: well, we don’t need to go there again, and we move on the the next new idea.
Bring on the dimples, and the jet-bottoms, and tinkler tails, and the Fat Pengui…no, never mind about that one… and the internal flex ribs, and everything else we can think of. Then we can enjoy all the good stuff that survives.
Yeah, design changes are fun for the designer, the surfer test pilot, and someone’s pocketbook.
Dimples seem to make the board loose, but loose is not good when you’re riding high trying to make a fast section. Not good also when you take off late and angled.
So maybe those golf ball bottoms are better reserved for waves that have little consequence.
And sometimes, you gotta compensate with slightly larger or more setback fins, negating some of the gains from a “looser” bottom config.
Go for it, you can always fill it to try the “flat” bottom idea.
all the tops of my boards look like that. I don’t notice any difference. (:
Michael Storer speaks lots of sense. (read his stuff about planing too.)
i dont think there is much point in going finless if you are going to have more drag than a fin and less sideways lift.