What is the fastest (least drag) finish for surfing? Is 400 grit the best?
Rusty touched on it in his surfline blog:
my VW needs paint but it will never drive like a race car 
care to expound?
if your standard 400 grit sand finish feels like ABEC 5’s , after onit is on you have upgraded to bones swiss .
my 10 foot noserider was my introduction to the stuff , had the board for six months before i tried it . it just glides better and felt better in textured conditions . best way to describe it would be " more wet " or " frictionless" .
good stuff
great analogy.
Blah blah blah lah la la la la
Sooo... you surf that good...you can feel the 400 grit finish....more power to you.
I suck at surfing...
think about all the sand and salt water rubbing around on your surfboard....does the board get better with more saltwater sanding or do you get more in tune with the board ?
Will the paint finish on your VW Van make it drive more like a Race car?
It cost $10 to park in the lot at Cardiff Reef.....or you can find a free spot on Coast Hwy...once in the water no one cares where you parked or what finish is on the bottom of your board.........
My wife says the Cardiff Kook is named ________........................... (Ray)......
Have fun...buff out that longboard......you won't feel the difference if you don't think about it.....it's not a Ferrari......
hmmmmmmmmm.....how come all those hot cars are so buffed out????
$$$$$$$$$$
Well, I personaly hate shiny polished boards. 400 feels soo much better. Each to their own though
haaa’’ put a gloss on some of the stuff geting built and it looks like shit
wet sands & optical brightner who gives a fig about the customer eh’’
now a well done wet sanded gloss bottom i can agree with
** cheers huie
**
A long time ago… I was told that the discovery of a sanded finish being faster (creating less drag) than a glossed, polished finish came from the sailboat industry and their research. Kind of like shark skin, I guess. Since makos are the fastest thing in the water, I believe it. Whether I can tell the difference or not is another issue, But there seems to be some valid science behind the concept, considering boundary layer molecules, laminar flow, and the like.
Ray,
I’ll bring some to plaskett…who knows, it might improve your surfing.
nyuk nyuk
In the book “Shape and Flow” there is a pretty decisive experiment with two balls of the same shape, size and weight, with the same air flow applied, but one ball has scratches 3 thousands of an inch deep. At speeds below 125 mph the smooth ball has less drag, and above 125 the rough ball has decisively less drag.
Air and water are both fluids, but aside from that, they’re very different when it comes to adhesive/cohesive properties. I’m not sure you can extrapolate those results to surfboard fins in a surfing application. Maybe you can… I’m just not sure.
Yeh, I am not saying that the data from a wind experiment would apply to surfboards in water, but the phenomenon (as a trait of how fluids and bodies interact) exists, so I would expect there to be a similar differnce in drag between two different finishes at various speeds.
It has been a while since I have read the book, but it is pretty clear that you can extrapolate the data between different fluids as long as the Reynolds numbers are the same.
[quote="$1"]
In the book "Shape and Flow" there is a pretty decisive experiment with two balls of the same shape, size and weight, with the same air flow applied, but one ball has scratches 3 thousands of an inch deep. At speeds below 125 mph the smooth ball has less drag, and above 125 the rough ball has decisively less drag.
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lots of differnet concepts being addressed here.
while the comparison of the ball to a 400 grit sanded surfboard is indeed an "apples to oranges" exercise, it is not because of any difference between air and water. You should be confident of getting similar results for the sphere test in both air and water if the tests are conducted at similar reynolds number (velocity/kinematic viscosityi)
the drag of sphere ( a very bluff body) is dominated by the low pressure drag of its wake due to separation of the boundary layer. At low speeds or with a smooth surface the boundary layer is laminar ( low skin friction). however it is highly suseptible to early separation and a large wake ( high drag ). when the surface is 'roughed up' the boundary layer quickly transitions to turbulent ( higher skin friction) but the added energy in a turbulent BL is able to delay sepatation and reduce the wake ( and resultant drag) . The reason for dimples on a golf ball.
Back to the sanded surface of a surfboard.
this is an attempt to reduce turbulent skin friction by limiting the lateral spread of turbulence in the boundary layer.
a google search for "riblets" or "microchannel" or even long chain polyners (polyox) for turbult drag reduction may explain the process better. They all are attempts to limit the lateral spread of turbulence in the BL
3M still markets 'riblet film' made for stars and stripes in the americas cup. (but you can't buy it)
The point is: sanding a surfboard length wise with 400 grit paper may reduce the skin friction of the board.
if you are planing, it's possible that skin friction is a significant part all drag components and a few % drop in drag may be measurable.
if you are a golfball, sanding the surface increases your skin friction but reduces the low pressure wake which dominates the overall drag.
****
If you are using ONITpro, i have no idea whats really going on.
but i bet if you can convince yourself to buy it,
you'll already have yourself convinced you're going faster.
imo
regards,
-bill
Yes… it’s 3Ms riblets film I was referring to. As far as 400 grit, I understand that at lower speeds, you can get the same effect out of grits as high as 120, but those are fairly low speeds for surfboards… in the neighborhood of 6-10mph. HIgher speeds reqire finer grits to get the same effect on TS waves. So maybe 400 is about right for surfboards???
[quote="$1"]
Y riblets film I was referring to. As far as 400 grit, I understand that at lower speeds, you can get the same effect out of grits as high as 120, but those are fairly low speeds for surfboards... in the neighborhood of 6-10mph. HIgher speeds reqire finer grits to get the same effect on TS waves. So maybe 400 is about right for surfboards???
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Folks doing these kinds of experiments seem to agree that the optimum dimensions for the groove are proportional to the BL thickness. GenerallyThe dimensions are defined by a specific height and aspect ratio but lots of different shaped grooves appear to work. personally i have my doubts about the dimensional quality of a hand sanded surface.
but i've certainly done my share of sanding in search of drag nirvana.
fast boundary layers are thinner than slow boundary layers
all boundary layers grow with distance traveled along the body.
so the height and width of your grooves should vary with board speed and length.
I'm not sure where you may have gotten the reference to TS waves.
tollmein-schlicting waves are typically the precurser to turbulence in the BL. I guess they still exist but all order is lost with the onset of all frequencies going nuts.
my only point is that riblets are only for turbulent BL reduction.
riblets are only added drag in a laminar BL.
-bill
If you are using ONITpro, i have no idea whats really going on.
but i bet if you can convince yourself to buy it,
you'll already have yourself convinced you're going faster.
i dont know how much faster i am going but it feels better.
when others have tried my equipment i dont tell them about it , most of them have a comment about mine feeling better.
I thought the use of riblets elongates the laminar BL, and sort of holds off the “amplification” (?) of TS waves, leading to turbulent BL.
Can you help me clarify this conceptually?
So all that wax and crap stuck to the bottom of my daily rider is slowing me down?