Speaking of shark skin. I was thinking about those “fastskin” materials that olympic swimmers use. They supposedly mimic shark skin. I thought it would be a good idea to lam it on the bottom of the board. But from what I’ve been reading, there is no significant decrease in drag that these skins provide. I just googled “fastskin” and a couple of scientific papers came up. Both showing insignificant effects.
One of the papers was saying that the “denticles” on the fast skin were too small to be used as vortex generators. They proposed that larger denticles might provide more drag reducing effects. This might explain Benny’s boat observation. I think those spray on liners have deep dimples and grooves.
3M makes an adhesive-backed film that, under a microscope, looks like the “hook” part of their Velcro. There are tiny hairs molded onto the film. This stuff was developed to coat the bottoms of America’s cup boats. The idea is to break up the surface tension of the water and allow a water-to-water interaction istead of water-to-sticky-surface deal. The fillm feels like sharkskin and is really expensive.
I don’t know how well it works - I just know they make it, and they say it works.
Yeah, I’ve heard of that stuff too. I’m not sure, but I think I remember reading somewhere that it was banned? -Carl
An aeronautical engineer freind made a comment during one of our discussions that the behavior of high speed air, and low speed water was VERY similar. An observation worth considering.
Bill,
Your friend’s training, and bread and butter, lie in understanding and predicting the behavior of high speed air. I trust his expertise in that domain implicitly. But unless he or she has invested similar time and effort in observing and understanding the behavior of low speed water, I’ll be more inclined to trust someone like, well, you. The point isn’t to diss your friend; just to point out that legitimate experts in one field sometimes tend to overestimate the carry-over to one similar. Very few people are trained engineers in both aerodynamics and hydrodynamics. That is why I advocate that the surfing community invest a little time and effort into tests that are more-or-less specific to surfing. Do we have the resources to test and validate everything from first principles? Absolutely not! But that doesn’t mean that we cannot do an occasional cost-effective, “sanity check” test to validate (or falsify) some of these principles and effects.
Personally I used to religiously use the Surfco “Ultra Glide” product below till they discontinued it. I believe the original formula was a invented by Paul Strauch.
I now use this religiously to keep not only keep my bottoms clean from dirt and wax but also to restore the seal of the gel coat on the outside of the board. And to reduce UV induced yellowing.
But it does seem to make a minor difference in my mind using this stuff
probably not good for the environment though…
I guess no better than the early 70’s when I was spraying on silicone lubricant and WD40 as well as Morey’s alkaseltzer crushed into a powder mixed with a tad of leftover resin thinned with styrene and acetone and brushed on the bottom of your board and then sanded a bit once you paddled out. Even waxed the bottom of my board with a bar of soap(another morey suggestion). Once even painted on a thin 1/16" coat of clear silicon sealant all over then bottom of my board as well as glued on that finely ribbed rubberpad some medicineman was selling back then.
30+ years later I don’t know if I’m a better surfer because of it…
same thing as the endless search for the ultimate diet or fountain of youth I guess…
I use Formula 303 a lot myself. I also take vitamins each morning. I’m not convinced that either practice is effective. Years ago, Car and Driver magazine did an evaluation of auto polishes - carnauba wax formulae vs. the then new poly or acrylic finishes. One of their conclusions was that for a transparent coating to effectively block UV, the critical factor was thickness, and neither product family was thick enough. Now, all the subsequent studies of UV shielding for sunblock, etc. could have produced some breakthrough or other. But absent that, the 303 doesn’t seem to be any thicker than an auto finish. BTW, I used 303 on my truck interior - once. I thought ArmorAll was slippery, wow!
BTW has anyone else tried RainX on the bottom of a board? Mine are now all sand finished, but I did use it on the last polished board I had, on the theory that if I was going to repel water, I wanted to see the effect of increasing the force of that repulsion. Unfortunately I wasn’t able to reliably perceive the difference, if there was one.
An interesting thing that I personally observed film of, was the Boeing Company, testing scale models of the 747
submerged in water and being towed forward at a “scaled” speed. I can only presume that in a general way, as stated, there are strong similarities between low speed water and high speed air. The engineer who was my freind was Walter Majcan, and I knew him from 1957 until his early death in 1962. During that time he had a significant impact on my understanding of what surfboards were doing, and an influence on my thinking as it related to surfboard and fin design. It was Walter who alerted me to the possible application of vortex generators to surfboards, and fins, in 1960. I’m NOT trying to engage in a pissing contest on the nuances and minutia of the two disciplins (hydro-vs-aero). The comment was to point out a GENERAL similarity, and to perhaps stimulate some thoughtful insight among some of the readers. Just to add another variable to this mix, surfboards operate on the boundry layer of two nonimmissable liquids. Air and water. An interesting read is the Phd thesis of Stephen Barker, on "Boundry layer terbulance of two nonimmissable liquids.‘’ I was able to pick up a few insights that I factor into my thinking. The point you make, is well taken. And you are correct about “experts.” Thank you for your thoughtful and well considered response to my earlier post.
BTW has anyone else tried RainX on the bottom of a board? Mine are now all sand finished, but I did use it on the last polished board I had, on the theory that if I was going to repel water, I wanted to see the effect of increasing the force of that repulsion. Unfortunately I wasn’t able to reliably perceive the difference, if there was one.
I did
but I don’t think the surface of the board is the same smoothness as windshield glass
I was always fascinated watching the rain fly of my windshield without having to use the wipers at highway speed after applying that stuff
I never could get a result on my board though
Of all the chemical’s it seems that Surfco was the best at not only cleaning your board but the response I got in the water. I used to buy all the $1.00 single packs I could get when ever I saw it. I’ll try and ask Skedelski what happened to it next time I see him in the water. 303 seems better for boards and cars.
Best result so far as far as speed and control in real life…
Alexander Gemini quad
Griffin 5-fin fish
Nothing to do with hard or soft just the overall design of the damn thing which I think everyone seems to miss around here. It’s never the pieces but the entire unit which includes the wave and the surfer.
No pissing contest from me. Insufficient back pressure at my age guarantees a loss :-> I can see that air at high speed would certainly be denser, and the possibility that compressibility may not be linear - meaning that there might be something like a log or square/cube relationship between density and the power required for further compression (I’m not certain where to research whether that is the case or not). That would probably make it behave like a denser, incompressible fluid. My preference would be to see the relationship tested scientifically, with all the trimmings - falsifiable hypotheses, controls, verification. I don’t think that will happen, because it would be costly, and I don’t see the financial return from this particular series of tests. But little, inexpensive, “backyard” tests can be valid, too. And it only takes one confirmed result that contradicts a hypothesis based on prevailing assumptions to call related assumptions into question. What would happen after that is open to question, but I suspect the results would make the original efforts well worthwhile.
However the yachts in the americas cup, introduced a rougher skin on their yachts to effectively hold a boundary layer of water close to the skin of the yacht, and since water / water drag is less than water / boat surface the yacht had a relatively small decrease in drag (1-5%)
I saw a website for a company that sold a hydrophilic paint for boats that was supposed to produce a water on water friction.
Back in the mid 80s-around the time Dennis Conner was trying to retake the Americas Cup, I was doing some work at a glass shop in Escondido. Art Collier was shaping sailboards for Pascal Maka who then held the world record for speed sailboarding. The boards that Art was building Pascal where these extremely narrow flat rockered darty looking things. These guys from 3M showed up with this film that they adhered to the bottom of the boards. They said they had done Dennis Conners boat with the stuff. I remember the stuff being absurdly expensive. Another thing I remember was being told that the surface of the stuff was microgrid of tiny staggered NACA ducts. And yeah it feels like shark skin.
Back in the mid 80s-around the time Dennis Conner was trying to retake the Americas Cup, I was doing some work at a glass shop in Escondido. Art Collier was shaping sailboards for Pascal Maka who then held the world record for speed sailboarding. The boards that Art was building Pascal where these extremely narrow flat rockered darty looking things. These guys from 3M showed up with this film that they adhered to the bottom of the boards. They said they had done Dennis Conners boat with the stuff. I remember the stuff being absurdly expensive. Another thing I remember was being told that the surface of the stuff was microgrid of tiny staggered NACA ducts. And yeah it feels like shark skin.
Atomized, man, you’re killin’ me here :-> You remember all of those details, how about whether it made the board go faster?
well ive noticed that when a plane travels quick through moist air you can see trails, which look like smoke, off wings and tail. The same can be seen when an F1 is at full cry in humid conditions. the air gets condensed into a liquid.
Surely by pulling a scale model at scale speed its replicating the forces of air. I have very limited knowledge on the subject but it makes well sense to me, then again i could just be wasting thoughts and breath haha.
sooo…whos got a plane?..and who wants to drag me behind it at scale speed on a nice 8ft gun?
Well honestly I don’t know. I do remember the boards that where built where taken to I believe was called “The Ponds” which was this place out by Palm Springs where all those magazine photos where shot with the wind power windmills in the background. There where these shallow long troughs filled with water about 2 ft. deep that where dug into the desert that they sailed in. Essentially one would sail in a straight line from one end of the trough to the other as fast as possible. It wasn’t much later after that the troughs where destroyed by the owner of the property because there where too many people tresspassing. The troughs weren’t all that wide so if you wiped out you would hit the dirt going over 25 knots.
I have pondered this question for many years, and I was always under the belief that a sanded finish was faster because the surface was already wetted. I asked this question to one of the many Aeronautical Engineers that are at the company I work for, and ALL of them said a gloss/polished finish is faster than a sanded finish.
They ALL said the same formulas/theories apply to both water and air. With that being said, I will try to explain what he told me in layman’s terms; a gloss finish doesn’t retain any water, it pushes water away, thereby making it faster. Water adheres to a sanded finish. Once water adheres to a surface it creates drag. To have the water removed from that surface; it takes quite a bit of force/energy to do so.
I hope this helps out …. I guess my next board will be a glossed/polished finish …
water ain’t air, air ain’t water and your board ain’t an aerocraft… snow is close though… reeeaal close. otherwise… well, … maybe we’re just going so slow it doesn’t matter a speck whether or not it’s smooth… the ocean is awe-fully powerful after all, no need to molest it. no?
The SeaSlide coating that you mention above, was the material that I was referring to about a year ago when this subject was discussed, and I had said…
“Or some of the Hydrophilic coatings that absorb water and leave a slimy, super slippery finish on the boards.”
This stuff works good but don’t put it where you need to hold on to the board as it is very slippery.
Interesting, it seems that it does the same job as detergent or coconut oil without actually dissolving. . . . and BTW it supports the sanded finish is faster theory as well.
Back in the early nineties we would use very fine water sandpaper on our windsurfing boards and especially the fins. It made a huge difference in the battle against cavitation. Really. You can imagine at this time we were starting to sail serioulsy overpowered and even at times wearing additional weight to hold larger sails. Ordinary fins would cavitate readily and cause a real mess… the sanding, it works! Just take a shiny fiberglass fin, hold it under the tap and watch the flow, now go sand the puppy and do the same. A layer of water adheres to the surface and that gives you that extra push to maintain laminary flow at higher speeds/angles of attack.
Interesting, it seems that it does the same job as detergent or coconut oil without actually dissolving. . . . and BTW it supports the sanded finish is faster theory as well.
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Aloha Roy
My experience with this material wasn’t so much an issue of speed increase. But it did seem that the water was able to redirect quickly and therefore the boards took less effort to change directions. Like it was on ball bearings.
I also found this to be true of super hydrophobic coatings.
True speed, as you know, is very difficult to measure and even harder to sense accurately. But both materials seemed very fast also. Yet they still felt different in ways not easy to describe. I would have to revisit those tests all over again and I don’t know if I can get enough waves now to get a worthwhile test! Ha!