The Visible Fin Tip Vortex... Underwater Video

It is so refreshing to read a clear statement on fin function.       It is always a pleasure to read your contributions.       

Aha, I found the record. The two purple Gullwing fins (with and without tubercles) do indeed have a well proven foil. Thanks to Hans’ and many decades of aeronautic research. 


You are too kind sir!

Thanks for this answer, wrc – very much sufficient in detail (for me) and answered my questions.

I took some more video with the camera held a bit deeper, and a bit further back behind fin on a lower drag mounting system.


The fin is one of MrMik’s pultruded carbon bar, not rod, laden G-whale 3d printed fins.  It is very stiff and strong . The carbon bar ‘leaf springs’ are adhered to each other, and to the fin’s interior structure, with gorilla glue. 


14 Mediocre rides, while the battery lasted( 37 minutes), were mostly short and entered sandy bubble laden water all too fast, where little can be seen.


I have filled in the voids in finbox before and after fin with the bases of previously broken fins.


The youtube video played on my laptop says HD and 720p resolution, but looks like 480i or worse, click 1080i  on settings and resolution is a bit better.


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Surfing with the camera is not a significant hindrance to catching or riding the wave, but bringing the camera to the beach, attaching it to board, turning it on, getting it to record at highest resolution and frames per second, and then surfing while wondering about battery life, makes the task less appealing than simply surfing without the camera.


I was expecting better footage, as the water clarity from above looked nearly as good as it gets, and I hoped the battery lasted longer, to when I got bigger better longer rides in less turbulent water farther from shore.  No such luck.  Oh well. Could have been worse.

Thanks for sharing! Interestingly I could not recognize any turbulences or vortexes around the fin area, but a lot at the rails. does it mean, that the “whale fin” really works like intended? It looks rather upright, suitable for narrow turns and the height and length give a lot of surface, resulting in good hold. Can you give us the dimensions, including width and foil and what kind of board did you use; I would guess its a mid to long with at least 8’ in length…
Again thanks for sharing!

I’ve raved about the G- Whale fin a lot  in MrMik’s thread.


But a shorter assessment is half the drag,  and similar to more grip/drive of a regular  shaped fin.  I’ll never willingly go back, as this fin makes riding this longboard, and my other longboard, so much more fun and interesting and confidence inspiring. The tail can be put up much higher in the wave face without the fin stalling, much more extreme angles more parallel toward shore can be achieved. Its faster quicker and looser, predictable and forgiving, and the only drawback, once one figures out the new shorter turning radius,  is when dragging kelp or weed, but it has to be a significant amount before it feels as draggy as the fin in the first video earlier in this thread.  

The  high aspect ratio, super pivotal nature is certainly not a feel everyone will appreciate, and it certainly takes some learning.  When I’ve gone back to a regular fin it always feels like the board is not going to swing fast enough back under me to maintain my feet during and near the end of a turn, and it just feels slow, and I’d often watch that section of wave I wanted, do its thing without me, and curse.   Nice and stable though.  Makes me thing a great noseriding fin is just huge and draggy merely to force one allow one’s tail to stay in the pocket  while perched on the nose, on a slow peeling wave.  Which is certainly rewarding and fun, but so is accellerating and making racier waves one though were peeling way to fast to make.


 There are a few visible tip vortices here and there with this fin but not as pronounced as with the other fins I have used when capturing video. Its a shame the battery did not last longer to When I got longer bigger waves farther outside as the tide drained and some locals left and I really laid into some bottom and top turns at higher speed.


This Longboard is a 9’7" x 3" x 23" traditional soft railed hollow cedar board that I made in August of 2003. It has been a very good friend ever since. It is very high mileage as I only ride shortboards when  the average set size is chest high or bigger and not always then either.  It weighed 21.5lbs when new without a fin or wax but is likely 25lbs now with repairs and reinforcement.

I’ve not weighed it since, as it Doesn’t matter.


 A relatively shallow nose concave transitions smoothly into a slightly rolled belly to a bit more of a V off the tail, but the going left side of the fin, has a small bit of concave on the side of the V, mostly intentional but once noticed, accepted.  Rails are more  down, 70/30 off the tail, one can easily see the water run up over the rail apex. I weigh 215 to 220 lbs and can duckdive it nearly as well as most can duckdive a shortboard.  It is fairly bladed out but duckdiving a longboard  is 90% technique and I can accomplish it with a 3 3/4" 9’6" too, just not as deep.  I dont have any roker or foil shots but a few have described it as bladed out, and it is a bit thinner than in intended with a bit of a crown at the center stringer, also unintended.


Not much nose rocker, a definite kick off the tail, never measured it for actual rocker numbers.  Pretty much my all time favorite longboard, and I grew up riding 1960’s era Greg Nolls and Webers on the east coast when not on a early 80’s style shortboard.


The pics below are from when it was recently built in 2003, and that fin did not compliment the board well, but it shows rocker and foil better than other pics I can easily find at the moment.

Been dreaming of this angle for years. Well done. I wanted to glue tell tales to the fin sides and bottom of a multi finned board.

I’ve been meaning to attach this to my thruster fin, and attaching streamers to all board that I use when towing the camera. 

I worry the leash will get entangled with the camera and perhaps rip it off, and going leashless would perhaps have the same results depending on wave size and the shorepound if/when I lose the board. 

The distance behind a thruster fin, and the camera depth, might require modifications to my existing tow equipment. 


If I could just throw money at new cameras and memory cards I’d be more willing to take more  chances, and record way more video. 

The battery life is also annoyingly short.


The you tube videos, hitting the space bar pauses the screen and the . or > button advances one frame and the , or < button rewinds one frame.

This is interesting

One time i was rinsing a teflon frying pan under the kitchen faucet and I noticed that the flow separated from the surface of the pan where there was nothing more than a scratch.

The flow separated and there was cavitation at that spot, From just a scratch! 

It’s repeatable and produces the same results each time.

You can do this yourself with a new unscratched teflon pan under running water  and then repeat the process after putting a piece of scotch tape on the surface.

At that point I started pondering the possibility, or difficulty, of producibg a board bottom that is so free of defects that there is no detachment of water flow (cavitation)

I just try to get it as right as I can and hope for the best.

Good Post!

I think what would be even more interesting is a self-propelled and self-guided camera. Early on, you would need to keep it on a leash, to keep it from getting hurt or hurting others.

It needs to be following the surfer’s board by actively seeking to stay in the center of the ‘Wake’. Where it needs not do much  to stay there.

Except for being alert and nimble enough to actively move toward the sweet spot when it is at risk of being lost.

It will take a lot of skill to materialise that sophisticated device at the right place and time. 

I’m in.



Some folks use SOS Pads, but I prefer 3M Scotchbrite pads and Blue Dawn.  Cleans those pans and frees up water flow.

Regarding Teflon:

"Surface Energy

In most cases, the coatings that we apply will provide a finish that is low in surface energy. Such a finish will give good non-stick and release properties. This is the main characteristic of the coating layer, when it is cured.

Non stick and release properties are not to be confused with low friction values. Friction is a measure of the resistive force opposing two objects sliding against each other. Non stick/ release, or low surface energy values are a result of intermolecular forces."

From Epic Kayaks

Should I Wax my Kayak?

" …a smooth surface WILL make you faster. The smoother, the better. You don’t want any bumps, scratches, or dried on crud disrupting the flow of water over your hull. If your hull is rough or oxidized, start by wet sanding the surface. Use progressively finer and finer grit sandpaper, all the way down to 2000 grit if you can find it. While 600 grit is the finest you’re likely to find in most hardware stores, auto body supply shops usually carry the ultra fine grits. Once you’ve sanded the surface perfectly smooth, use polishing or rubbing compound to make it even smoother. An orbital buffer with a nice soft pad will give you the best finish. Now you’re ready to race."

With this in mind, I agree with McD. 

You could use Scotch-Brite pads to keep your SB bottom surface smooth and clean.


Interesting. The Board Lady always said that you don’t want that mirror like finish on a board. She says it causes the water to bead, which actually creates drag. Her suggestion was to sand no higher than 600 grit. Here’s her words:

In extensive tank testing for world-class racing boats, it was established 40-some years ago that a glossy surface has substantially more drag than a matte one. In tests I was involved in for an America’s Cup boat, we found that simply sanding a glossy bottom with 600 grit paper, reduced the surface friction by about 5% at ½ hull speed, i.e. at about 4.5 knots. Instead of sticking to the glossy bottom, the water molecules would be “tripped up” by the minute ridges left by the sandpaper. This slight turbulence would reduce the thickness of the film of water being moved along with the vessel (the “boundary layer”), and thereby reduce the overall drag.

Surfboards are traditionally finished super-glossy-shiny. Windsurfers, on the other hand, have long since followed the lead of sailboat racers and taken the gloss off the bottoms of their craft.

So, it seems to her (and the yacht racing industry/windsurf industry) that yes, a smooth board will go faster but there’s such a thing as too smooth. 

If this is the case, it’s interesting. Do you want a board that looks all shiny and pretty or do you want a board that is faster?

I have read that too.  I would not sand to 2000 or polish.

The point is, cleaning/smoothing the bottom with the right Scotch-Brite pad is plenty good enough.

And non-stick/release surfaces do not equate to lower friction just lower surface energy.  

Low surface tension typically causes water beading.  That would be related to properties of water and the surface material itself.  Water does not bead up on glass.  It spreads out.  (Glass is a polar material.)

Greg Liddle has been saying this for years.  The boards he used to stock at the Beach House in SB were sold with a full page instruction sheet on why and how to sand your new GL.

I would love to see that sheet. I wonder if Kirk Putnam has one. 

Say there are two absolutely identical boards under the feet of a capable surfer, one is wetsanded to 2500  then polished to as shiny and as smooth as a surfboard ever got. The other has 400 grit scratches in the direction of water flow, or crosshatched, which ever is the current flavor of the month as ‘fastest’.


I doubt The most sensitive and articulate surfer, on an uncrowded pointbreak on a holding swell on a windless day, in a double blind test, is going to be able to discern any difference in speed between the two boards, and a gps tracker will also likely show no statistically distinct advantage to either. 

Now which board requires less effort/time  to make? 

What are the latest foiling America’s cup boats doing?  Their hulls and foils look plenty glossy shiny to me and thier budgets are almost unlimited…


Now two identical boards, either wetsanded to 400 or glossy, but one has regular traditional looking fins, and one has fins with considerably higher aspect ratio.  The HAR finned board will be obviously looser and faster, which will be  instantly noticeable, perhaps  even when paddling.  Whether the surfer can get used to the shorter turning radius and the different places to extract speed from on the wave face, with HAR fins, is another matter. It is a very different feel, like someone gave your car more power, but took away some braking ability and the steering wheel turned the wheels more, faster.

If one gets lined up waves and just wants to go as fast as possible, there is no faster fin.  Controlling that speed through turns is another matter.  It is very twitchy and some resistance is certainly desirable, just like brakes are on a car or a parachute is to a skydiver.


That elongated raked tip of standard surfboard fins, is a beautiful elegant self centering, stabilizing, turn fighting, drag inducing feature.  If one wants a faster board few will ever be able to notice 400 grit crosshatching or parallel scratches in the direction of waterflow, versus the smoothest polished gloss coat in history. They will like whichever their or other’s preset opinion has already dictated.

But few surfers would not be able to notice the significantly less draggy nature of significantly  higher aspect ratio fins. Any minute advantages in drag of glossy vs wetsanded  hulls, will likely never be positively quantified, whereas   higher aspect ratio fins can easily be, and perhaps even before one gets to their feet on a wave.  

My impressions of experimenting heavily with ridiculously high aspect ratio rail fins on a shortboard, is that the tail holds way higher in the wave face and rockets forward, instead of stalling,  requiring that the surfer point the board back shoreward, hopefully in time and avoid that area in the future.  HAR fins are Likely bad for stalling for tube but insane for racing what otherwise would be unmakeable wave face.   This ability to place the tail higher in the wave face without stalling with HAR fins, is something I would love to see under the feet of a top rider in both gutless dribble, and barreling waves of consequence. 

I’ve been told when I ride my shortboard with those who are used to my style, that it appears that I am gaining speed unnaturally, the observer expecting me to get hung up, being too high in the wave face, but accellerating instead, and then wondering what to do with all that extra speed, which is also how HAR fins feel underfoot in my experience and opinion.


On my traditional soft railed 25Lb log, high aspect ratio fins obviously paddles faster, catches waves way easier and earlier with less effort, and is way way faster through turns, and in a straight line, and the turning radius can be pushed much shorter.  Long nose rides on slower peeling waves, are more difficult as the board accellerates instead of the tail getting stuck in or behind the lip.


Absolute highest possible speed is not always needed, in fact much of wave riding is about slowing down in a controllable and stylish manner, as opposed for pumping for speed to reach the slopey shoulder ASAP.  If the goal were maximum possible speed always, any rake in fins would be designed right out of the equation.  They’d be completely upright and only big enough to prevent the tail sliding on the initial turn parallel to shore. With more speed attained they would ideally retract for even less drag. If attaining  highest possible max speed  each and every wave were the goal, we’d be riding rockerless finless skimboards, and riding them as high as possible in the wave face always, if one could even catch the wave under their own power.

I see some of this years crop of tow boards have thinner much higher aspect ratio fins now, and those guys are going fastest of all, and need to. 


I’ve always seen these glossy vs wetsanded finish debates to be worthless, from the first time some surfshop owner back in the mid 80’s  declared that all glossy boards are inferior to the new sanded finishes he was selling and charging more for.  And then having to listen to everybody parrot what he said as if sheer repetition made it true, for the next 35 years.


Show me actual quantifiable data, rather than repeating subjective impressions by proponents on either side.  If One or the other is determined to be actually faster by actual data collected by knowledgeable experienced people with the tools and temerity to collect it, I’d bet it is such a tiny amount of difference that a 1/64" less of tail rocker or a few degrees less of fin rake would have vastly larger impacts on average speed to the average surfer.


You want a noticeably faster board? Try a higher aspect ratio fin, you will trade increased speed for some loss of control, but your eyes will be opened if your mind is not closed.

You might like the feel, or you might not, and that’s opinion, not fact.


Seems the smooth gloss vs sanded is purely subjective opinion, with weak arguments yelled from either side with dubious motives behind them.

Whats easiest and most profitable?  Sanded finishes.  Market it as faster to the gullible Nimrod A Public, and win win.





Relax.  I was addressing rajon’s comment about Teflon and McD’s comment about cleaning with a Scotch-Brite pad.

I was also pointing out surface energy and surface tension do not necessarily equate with friction.

I’m not arguing for or against smooth vs. sanded.

Eva, Epic Kayak and America’s Cup racers all agree that a clean hull is a faster hull.  I’ve even read an Eva comment that board bottoms should be cleaned with a Scotch-Brite pad.

Bottom line, cleaning your board’s bottom surface with the right Scotch-Brite pad is likely to be as effective as anything.

Pretty sure fins generate a significant amount of drag – surface area.

When an old thread gets “bumped,” sometimes it takes a new direction…

No snarky tone was intended, I’m not all worked up. thread drift is fine with me.  


Small incremental improvements are still improvements, even if they can’t be quantified for our intended purposes. 


The latest America’s cup boat, Defiance, apparently uses 1000 grit forward and 600 aft, optimized for 12 to 16 knots, and scratches run in the direction of flow, not cross hatched. Not sure if this is both flying hull and or the foils themselves. This is from a consultant on the design team.  No doubt they can quantify the differences and tiny percentages of drag reduction, which can mean win or lose.

Huge difference from the guy proclaiming that ‘one should never gloss polish and wax your surfboard hull, as it will make it noticeably slower,’ which has been parroted since the mid 80’s and I am not pointing any fingers here at Sways members, more thinking about some douchebags from my past who used to say so as if they were authorities, when they are really cerebally challenged and should state nothing authoratatively.


I’ve had my longboard hull and rails all rough from taping off small potentially  watersucking dings/cracks sanding lightly within the tape, and painting a layer of epoxy over them, then pulling the tape and calling it water tight and good enough. Only when I accumulate enough of these all over the hull and rails, do i bother sanding them all  smooth and making it look and feel purdy and smooth.


Last time I did so, I expected to feel an improvement, was hoping I would. I couldn’t. I however can easily tell when I ride a 9mm thick 3d printed fin vs an 11 or a 13mm of the same exact planshape, in trim speed and turning confidence, or when i move it 3/16" forward or backwards in how it turns.   The super rough  surface texture version was however noticeably draggier than smoother.

If max speed looks to be the most desirable call for the conditions, I am going with the thinnest stiff fin. If I’m feeling rusty and the waves are peeling slow, the fatter fin is  way more desirable underfoot.  The best all arounder splits the difference and then flex and surface texture would be the remaining variables to dial in, but these refinements get lost in the noise of limitless variables which occur when riding a wave, even at the same location for years and years on the same board. 


I’ve been epoxying then sanding the 3d printed fins as smooth as I can, but the turbucles and the Printing striations make this difficult. and I am likely achieving rougher, rather than smoother before the transition from laminar to turbulent flow, which is apparently scientifically desirable at this point in time depending on whose science one wishes to believe.


But my rough dirty hull vs a smooth impression, was formed on an old school soft railed longboard, which has a limited top speed anyway.  My point is if one really wants a noticeably faster board then a lower drag fin(s) is/are much more easily noticed than surface texture, in my experience on both long and shortboards.  

If any regular Joe tells me they took their glossy polished board, and wetsanded it an it is now way faster, I not going to put any weight to their words past present and certainly not in the future. 

I’m not going to pursue 1000/600 grit scratches in the direction of flow.  I’m gonna keep my boards hulls clean  glossy and waxed, and not stress surface imperfections as I accumulate more epoxy to seal potential watersuckers.  I’ll call them vortex generators and claim they make me go faster.  Don’t believe it, prove me wrong.




If I saw actual quantifiable professionally accrued data that 5% less drag can be  achieved by a properly sanded finish, versus a waxed glossy polished one, at the speeds I am achieving when riding a wave, then… I probably still wouldn’t bust out the wet sandpaper  or scotchbrite and go to town.  And my epoxy ‘gloss’ coats do not  even come close to the perfection acheiveable with PE gloss coats.