watched and experiment with a smooth shinny ball and a tennis ball thrown through a small short tunnel simmilar to the shape of a pipe…the tennis ball sjkided through and the shinny smooth ball stuck to the surface and came back out the entrance it went in…it showed me that a rough surface will have less friction then a polished smooth surface…how rough can we go before it slows us down?
EVERY experienced windsurfer, speeds around 28-40mph, agrees a sanded 6-800 finish, in the direction of waterflow, is the fastest.
have they tried the real rough finish with windsurfers…i hope so…I know there is guys out there working on this…I got my first one that was almost like fur on the bottom.in 85…but I didnt test them properly…by the ball test…the fur looked faster through the pipe then the shinny polished rubber ball…it may have only been the ball being rubber that may have stopped it not the shine.
Hello Cheyne,
There’s one really rough surface which is very fast, and that is the shark’s skin. You can’t do it with sandpaper though! You have probably seen photos of sharkskin under a microscope . . .there are thousands of tiny ‘denticles’, each one looks like a miniature starfin (or cmore exactly like a cruciform fin). all these denticles gang together to direct the water flowand preserve laminar flow. this is what started me out on the hydrofoil thing only I built two huge denticles instead of thousands of tiny ones.
There’s also the microgroove theory. Maybe if you could sand fore and aft very accurately you might get micro grooves with rougher paper?
Golf ball sized dimples are slippery’er, but slide sideways as much as forwards, and needs bigger fins, thus increasing drag, thus slowing you down again.
Windsurfers spend thousands of dollars testing, to find the fastest bottom finish.
EVERY expert windsurfer still says…sanded 6-800, in the direction of water flow, and the percentage gain, being more mental than physical, might be…2%.
You see, speed is directly affected by your actual board speed, your trim angle, your fore aft besides side to side lean, your rail shape, size, and form, WHERE you place your board, at what angle, you body weight compared to surface area compared to trim angle etc etc etc… NOT MEASURABLE, by any means!
yeah the surface seems very minimal affect on speed, when you talk dimples its more the shape…my friends the willis bros and Mark Foo used them big and small I ve tried them towing and they were fine…
speed…most of it seems to be at the top of the wave…top 1/3…I use finish coats buffed for the protection longer lasting…now im thinking a sanded finish coat…do u wind surf?
Been shortboard windsurfing since '83, mostly around 110 days a year.
Been on the speedsailing circuit here (WestCoast USA) from '87-90, with very competitive speeds for my weight, but big guys rule here.
In surfing, I’ve always believed any properly finished board is fast enough to get the job done. The pilot makes the choices, and the board has to do it’s part, but the wave decides what the pilot can really do.
I basically taught the old SurferMag board design editor, of like '77-83, how to surf, and shaped a bunch of boards those years.
Speed doesn’t seem nearly as important as pilot ability.
Those speed windsurfers are crazy. Had e college who ripped the tendons inside his hands in strong winds. Won the race, but can never do it again.
One thing I don’t understand is why a rough surface is faster. Won’t a rough(er) surface pull more water with it when it moves thus create more drag and be slower? Or is it other forces at play? I know that snowboard will be much much faster with grooves in the length direction in wet snow. If the snowboard is smooth in wet snow it will stick. You can basically be standing still in a steep hill just from the surface tension. Grooves, siclicone and graphite wax is a good remedy. I wonder if it’s the same forces at play with a surfboard as well?
regards,
Håvad
But remember, the same structured snowboard bottom is uselessly slow in deep powder, cold conditions! Those structured Burton bottoms are horrible for cold snow.
Remember, the percentage of speed and glide difference is almost negligible.
Sanded attaches water to the board. Water to water friction is less than water to board friction, so is faster…more a feel than anything measureable.
And target speed of surfboards is similar, but slower than sailboards.
Pilot ability more than compensates for any shortcomings in bottom friction.
Quote:
But remember, the same structured snowboard bottom is uselessly slow in deep powder, cold conditions! Those structured Burton bottoms are horrible for cold snow.
Remember, the percentage of speed and glide difference is almost negligible.
Sanded attaches water to the board. Water to water friction is less than water to board friction, so is faster…more a feel than anything measureable.
And target speed of surfboards is similar, but slower than sailboards.
Pilot ability more than compensates for any shortcomings in bottom friction.
I hate Burton boards anyway… 
I usually sand the bottom of my boards myself. But you’re right, dry snow(including the man-made one) requires a very fine stucture and very hard wax. The difference in a well prepped snowboard is remarkable. Also the wax is supposed to create a very slight friction which is supposed to melt the snow so the board rides on a thin layer of water which is supposed to have less friction than plastic to snow…
I’m not sure if it really matters much on a surfboard but even a 2% speed increase might be what get’s you past that section as long as the pilot is any good anyways.
regards,
Håvard
ive heard things about water wants to stick to a smooth surface…ive tried rough and smooth,cant really prove wich is faster…all depends on the wave i guess,or the surface i cant remember wich,try the same board rough and smooth,thats probally impossible cause your mood,wave,etc…changes…two boards the same, one smooth one rough…well thats proballay out of the question too…unless a machine does everyting but ride it…
Hello Lee,
According to information presented by David Vacanti at http://www.vacantisw.com/foildesign.htm ,
an optimal low drag surface makes more difference at low speeds than it does at high speeds. This might seem to fit in with your observation that speed is more about rider input. I have noticed the ‘slippery’ feeling of a slick bottom more when gliding on slow sections than when booting along on fast ones.
hey leedd a guy dropped around here a few weeks back,was telling me he was on the sailboard circut in the late eighties…ive surfed with him heaps , even competed on the same surf team ,and i only just found out he was a professional sailor…
you know rich meyers???
i think hes just gone back to hawaii recently , for a holiday…
yea rough is better …as long as its microscopically rough…
you want to trip the boundry layer to be turbulent,
so then your riding on a fine layer of turbulent vortices,like ballbearings…the rougher it gets the larger the ball bearings get , which then starts to create more drag again coz your turning over more water , which takes more energy…
laminar flow has the most drag …drag is least apparent at low speeds …
viscous drag is surface area x the square of the speed…double the speed 4 times the drag…
theres some basics…
regards
BERT
I think Rich was a central coast surfer, mostly known for wave sailing but not too sure about slalom racing. I know he didn’t do the speedsailing circuit, at Klickatat, Doran Beach, Ponds, SanLuis Forebay.
He was one of the early pioneers, probably before my time, and possibly still much more famous after.
Is he the stocky blond kid with the big shoulders?
I’ve got a chart of “Allowable Roughness” based on speed through the water, that I got for long distance sailboat racing bottom preparation.
800 grit is recommended from 15-19 knots. 20-24 knots recommends 1000 grit and 25-32 knots recommends 1200 grit finishes.
Good stuff there… and makes sense!
Most windsurfers need to break that 15-19 barrier to get up to top speed.
At top speeds, most recreational sailors go about 25-30mph, maximum, as chop and other factors come into play.
Speed trials sailors often hit over 47mph, with the world record around 55mph. They are treading on new ground, get launched, hit terminal speeds, are mostly 250 lbs monsters wearing added weight riding tiny, 16" wide boards.
Seems it’s much harder getting up to speed than maintaining or increasing speed once you get close to top speeds.
viscous drag is surface area x the square of the speed…double the speed 4 times the drag…
Which is why longboards tend to "top end’ at lower speeds than shorties.
I’m finding that I’m in so much agreement with what is being written of late that adding anything is just redundancy.
Surely this means then that the rougher the surface, the more drag + therefore the slower the board. A gloss coat is therefore faster?
goin through France a guy was waxing the bottom of our boards 4 the contests and this made a difference waxing the bottom of my board and polishing…leed did u do this with the windsurfers? to greg how are u mate?..you still throwing it up there…where u surfn these days…still east?
WOW! an agreeable thread concerning surface texture and speed!!
Cheyne I do think that wax and polish can be faster. It probably adds some texture (microscopic) to the bottom.
Much of this has been discussed before here at Swaylocks.
A microscopically rough texture affects the surface tension between water and surface creating a “Lotus effect” where the water beads up and runs off easier.