What a drag!

Any discussion on shaping, designing, repairing and riding surfcraft of any type or shape. Also a good place to ask the 'what board should I buy?' question.

What a drag!

Postby Poo Stance » Thu Mar 22, 2012 1:55 pm

Fooger me, I don't think I've ever started a thread in here. Sorry if it's diluting the quality. I'll wont take off my coat. Sorry if there is already a thread on drag.

I'm always thinking about board design and never really understanding it. So in my wonderings through cyberworld I've recently found these links and thought I'd share with everyone.

This one is a nod towards More's Dimple Boards. http://www.zipp.com/technologies/aerodynamics/ablc.php#
A long time ago I read in New Scientist about a material being considered for use in F1 which would reduce the drag from the body panels. I wish I could find the article now but proving hard.

Anyway, more drag related articles which may be relevant to any experimental board designers...

http://www.newscientist.com/article/dn1 ... ights.html
http://www.newscientist.com/article/dn1 ... -subs.html

This was all kicked off by a comment made about blue fin tuna I read under that Leohr's theory on Sways...
"Nice job greg. I have a copy of this somewhere in my computer but it's nice to see you posting it here so everyone can benefit. I sent the link to one of my team riders, who is a student scientist in the field of fish morphology. That basically fish design. He totally agrees and he tells me he never agrees totally with anything! I cant post the the Newton Forum anymore but i found a lot of nosense there that can easily be addressed. First, form follows function. If you are to live and propel yourself through water which is 800 times denser than air you will no doubt have to have some special design features that enable you to survive. Such is the case with the Atlantic Bluefin Tuna. Now, what survival advantages does a huge piece of meat like that have over the shark? Speed. The ABFT which can exceed 1500 lbs. (about a VW Beetle) has been clocked at speeds reaching 65mph. It can be assumed without much debate that there are no unnecessary design features on a fish with these statistics. In fact, what is there is absolutely necessary to the fish's survival. Such is the case with the array of tiny finlet's. I have researched them and have been in contact with the only scientist in the world, at Harvard btw, who has researched them and she concluded, among other things, that they contribute flow to the tail fin. Now, the difference between using a fin as a rudder as the concept of fin exists in most surfers minds and using a fin as a propulson device as do Kelly and Pat Mulnern, this opens up entirely different approache to the way we think about fins. Drag a dead tuna through the water and you can measure the drag created by the fins, just duplicate the experiment with the fins on and then cut them off, but that same tuna as a swimming fish will use the fins to advantage. ``As the finlets contribute flow they actually reduce the drag associated with chaotic turbulence and separation of flow and turbulent bubbles created by sharp turns all of which contribute to drag. Therefore, by adding a device in front of a fin it is possible for a rider to increace speed by altering a number of conditions of flow around the fin. I have created such a device, called a MVG. Placed in front of the trailing fin it contributes flow and helps increase speed production while also contributing flow to fill in the turbulent bubble in a sharp turn and thereby allowing a rider to maintain speed through turns. I have spoken with the NASA engineer charged with developing MVGs for aircraft such as the F118 and ``and the Boeing 737 I flew on last week from Cali. I counted a total of over 40 MVGs of varying sizes on the wings of that aircraft. So, this is not a totally new technology. Not at all. The NASA engineer said, Mark, ""You cant go wrong imitating the Creator."" Let's just keep our eyes and minds open to nature and the possibilities created therein over the millenia. In fact all invention comes from observing nature. Where else you going to look? That's physics ...and a coke bottle is just silly."


Which lead me to look into MVG (mini vortex generators) on planes...

Image

and wonder how they could help surf board designers. I'd say that this is probably something Roy was thinking about with this...

Image

Anyway, just putting it out there for thought. Any comments welcomed.
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Re: What a drag!

Postby mister-griffster » Thu Mar 22, 2012 2:48 pm

Interesting that we believe that drag is the result of fin and still trying to grasp what Greenough worked out 40 years ago....

One natural device is to use a 'thumb' bolt if you have a box fin - essentially disrupts the water pressure just before it gets to the fin (tho whether this works the same or no i have no clue.. just saying)

This concept to 'pierce' the pressure of water / air will indeed improve the efficiency and reduce drag... but interesting the one of the main reasons that a tuna can go fast (apart from it's slipstreaming / power to weight ratio / general foiling is because of the 'resistance' of it's skin.

Have a look at a human in slow motion swimming and you'll see that our skin is distorted, deformed and thus creates drag - look a a dolphin or tuna doing the same thing and their skin remains firm / sleek and well shaped. This is a main consituent of reducing drag on the whole.

So, to my (tiny) mind some of the work being undertaken on the surface of a board, the distortion and breaking the tension of the water across the surface is where the real payback is.... One reason the wooden boards will go faster is that the mico abrassions created in the natural material break and release the surface tension i.e. same principle behind golf balling....
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Re: What a drag!

Postby Poo Stance » Thu Mar 22, 2012 4:09 pm

mister-griffster wrote:Interesting that we believe that drag is the result of fin and still trying to grasp what Greenough worked out 40 years ago....
I don't get it? You mean the fin doesn't cause drag? Or that we think the fin is the only thing that causes drag?

What's the point of drag anyway? Is it just to slow us down and help us control our decent along the wave?

Re: the skin in water. Did you have a look at the 2nd NewScientist link? So what I'm trying to fathom is, could you stretch a piece of cloth/skin across the bottom of your board and create the same amount of drag a fin does? And would that help you in controlling a board in anyway?

Have a look at this too http://www.grc.nasa.gov/WWW/k-12/Virtua ... ndlay.html
Thinking again about More's Dimples.
So the boundary layer gives any object an "effective" shape which is usually slightly different from the physical shape
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Re: What a drag!

Postby royal » Thu Mar 22, 2012 5:26 pm

MVGs - here's a quick and easy test...

take your bar of wax, flip your board over.... :wink:

kidding, but in reality, you could shape some onto the tail of the board and see if you feel a difference.

I've had some of Tim Stafford's fins in my hands for what seems like eons trying to make a board to suit... maybe add some MVG to the outline... :-D
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Re: What a drag!

Postby mister-griffster » Thu Mar 22, 2012 5:49 pm

I don't get it? You mean the fin doesn't cause drag? Or that we think the fin is the only thing that causes drag?


The fin definitely causes drag (for example 3 fins have more of a drag factor than a single) - Just saying that our focus tends to be on fins because the're the 'sticky out' bits and this we think that the bit that sticks out is th only cause of drag (as it's the most obvious)

For further MVG's take a formula 1 car - go back 15-20 years and they were pretty smooth and slippery - rounded and beveled - look at them know after 20 years wind tunnel testing and they're all points, and weird little shapes that at first doesn't seem to correlate with our understanding of 'flow' - what we now understand is that if you 'pierce' the surface tension then less drag will be created. When travelling at speed the substance you are travelling through (air / water / butter) has a greater resistance and density = pierce that and create a disturbance to that surface tension and you path will be faster, more fluid and create less drag...

Drag is simply the efficiency of the release of the containing substance... if you can release that substance faster and more efficiently then you will have lees drag (hence the foiling of the fin shape / rails etc)

Enough of my arm chair physics tho - there's some chaps with a far better understanding that I who could explain the concept more thoroughly. (BTW - most predatory fish have these smaller fins either infront of the main dorsal, or before the tail.

I didn't read the New Scientist link, but why would you want a fin to slow you down? (assuming you do not want to noseride in which case drag is important) - surely the aim is for less drag / more (controllable) speed?

No idea whether a covering would work, but simply rub the bottom of your board in parallell strokes with some wet and dry and get the gloss off - that will create mico-beading and disruption of the tension of water molecules - same effect - now i will happily wager that if you do that, scientifically you may prove that you are travelling faster but in reality you won't notice it.

By far the most important factor in this equation is shape and whether the sum of it's parts come together.
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Re: What a drag!

Postby Roy Stuart » Thu Mar 22, 2012 7:36 pm

mister-griffster wrote:
Drag is simply the efficiency of the release of the containing substance



No it isn't, quite apart from the fact that you should have said 'inefficiency' .

:roll:
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Re: What a drag!

Postby mister-griffster » Thu Mar 22, 2012 8:32 pm

I could have said, mnwananheahn en ann thhhhbbbt, but I didn't - I could have said anything that pops up in my tiny little mind - but I didn't - I said efficiency - quite right Roy, a better word would be 'inefficiency' in that context - but when you're bunking off work to contribute to a forum then hells, i aint got time for no spellchecker man.... now put the red pen away, in the same draw as you English doctorate.... how's about enlightening the discussion with the points raised about that fin of yours... :roll:
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Re: What a drag!

Postby skimmer2 » Thu Mar 22, 2012 9:33 pm

When I was into kayaking/playboating many moons ago they brought out loads of dimpled hulled kayaks - you could spin on them very easily as the water displaced. Think of a golf ball....they are dimpled - they have way less drag throught he air than a smooth ball.
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Re: What a drag!

Postby Roy Stuart » Fri Mar 23, 2012 4:05 am

mister-griffster wrote:
quite right Roy, a better word would be 'inefficiency' in that context - but when you're bunking off work to contribute to a forum then hells, i aint got time for no spellchecker man.... now put the red pen away, in the same draw as you English doctorate.... how's about enlightening the discussion with the points raised about that fin of yours... :roll:



The main point is that you are incorrect in stating that "Drag is simply the (in)efficiency of the release of the containing substance"

Actually drag is composed of form drag, induced drag and skin friction, it isn't simply a matter of 'release'.

The tubercules reduce induced drag and increase lift, as well as increasing the angle of attack capability. The effect is noticeable especially but not only when pushing the fin hard. The feeling is different as there's not that pressure wave buildup which happens with conventional leading edges, the fin just seems to spring back with a lot more power and also feels more accurate when going rail to rail, no vague spot during the transition. The advantage can be used to make thinner and or smaller fins, or just lower drag higher lift versions of existing fins.

The tubercules need to be foiled properly though not just cut out like saw teeth.
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Re: What a drag!

Postby kayu » Fri Mar 23, 2012 5:23 am

..without drag , surfboards dont work.....its a very misleading word.. :wink:
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Re: What a drag!

Postby Roy Stuart » Fri Mar 23, 2012 5:26 am

What a misleading statement, drag isn't required in order for surfboards to work it's just an unavoidable by product of movement and lift production.

You've been reading the myths perpetrated by the soup brained geriatrics on Swaylocks, watch out or you'll become one!

If drag could be reduced by 99% surfing would still occur, but much higher speeds would be possible.
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Re: What a drag!

Postby kayu » Fri Mar 23, 2012 5:42 am

Roy Stuart wrote:What a misleading statement, drag isn't required in order for surfboards to work it's just an unavoidable by product of movement and lift production.

You've been reading the myths perpetrated by the soup brained geriatrics on Swaylocks, watch out or you'll become one!

If drag could be reduced by 99% surfing would still occur, but much higher speeds would be possible.

Re-iterate =surfboards wont work without drag... :wink:
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Re: What a drag!

Postby kayu » Fri Mar 23, 2012 5:44 am

Roy Stuart wrote:
If drag could be reduced by 99% surfing would still occur, but much higher speeds would be possible.

......now thats misleading !
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Re: What a drag!

Postby mister-griffster » Fri Mar 23, 2012 2:36 pm

Actually drag is composed of form drag, induced drag and skin friction, it isn't simply a matter of 'release'.


Fair enough old boy - I'd concur with that - as I said, someone with more of a scientific background than I could term it better...

Just a side-track issue for any shaper to contribute on - The claims you make for the fin Roy ( I do not dispute BTW) and others claims on surfboard science - can we establish the nature of validation? I guess what I mean is that there's a lot of theory there, but a theory (as in scientific theory rather than 'just throwing it out there' kind of theory) requires observation as proof. How does a shaper observe these scientific principles exactly?

For example, the theory of the physics can all be gained from text book, but only direct observation in practice can validate. Therefore if this observation comes from riding a board (either by the shaper himself or a surfer who feeds back information to the shaper) then the observation is still subjective. Observation and measurement can only be validated in some kind of 'test' environment - i.e. the equivalent of a wind tunnel for a car (here I'm thinking of underwater photography of a boards performance in a wave pool).

It seems to me that the majority of surfboard design is still in the R+D phase - made by supposition and subjective input and not validated by scientific methodology and proof (BTW, I don't have a problem with this some of the best things that have ever been made are the result of 'happy accidents'). Just throwing it out there as it would be real interesting to know how claims could actually be validated...

BTW - Happy to set up a surfboard R+D testing facility if someone has the ways and means - I'm thinking McClaren HQ for boards... :lol:
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Re: What a drag!

Postby Black » Fri Mar 23, 2012 3:30 pm

"skin friction" that's my kind of practical experience right there! :-)
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Re: What a drag!

Postby Rickyroughneck » Fri Mar 23, 2012 11:17 pm

Roy Stuart wrote:What a misleading statement, drag isn't required in order for surfboards to work it's just an unavoidable by product of movement and lift production.

You've been reading the myths perpetrated by the soup brained geriatrics on Swaylocks, watch out or you'll become one!

If drag could be reduced by 99% surfing would still occur, but much higher speeds would be possible.

Hmm it depends, I doubt that skin drag accounts for much of the total drag. I would expect most of the drag to be from the displacement of water.
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Re: What a drag!

Postby Roy Stuart » Sat Mar 24, 2012 2:13 am

In fact the ratios change as speed increases, at higher speeds skin friction drag tends to be dominant and at low speeds the form and induced drag are relatively higher.

At low angles of attack induced drag is lower, so it all depends upon the situation.
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Re: What a drag!

Postby kayu » Sat Mar 24, 2012 2:37 am

Fins are a major cause of drag in surfboards(appendage drag)......they are very usefull things !....surfboards should be designed to manage drag , to attain a required performance ......
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Re: What a drag!

Postby Poo Stance » Sat Mar 24, 2012 8:16 am

kayu wrote:Fins are a major cause of drag in surfboards(appendage drag)......they are very usefull things !....surfboards should be designed the manage drag , to attain a required performance ......


This is what I think. And now I'm wondering how different areas of the board away from the fin can be used to manage the drag in such as way as to control performance equally as well as fins do.

Re: Theory and validation. If an experienced rider can feel the change in handling characteristics due to a singular change in board design from an identical one, and ridden in as similar waves as possible. Then that's scientifically good enough for me. How often this actually happens I'm not sure though.

There has to be some numbers and equations out there which detail which areas offer the least/most drag and to what ratios. As well as some sort of scale of drag to viscosity. Not that I'd understand them anyway :?

Anyone seen these guys (from N Devon)... http://www.hammerandthresher.com/surfboard_technology/

Image
Image
Image

any ideas on how this would work? Seems like it would have some effect on the 'boundary layer', but only over a small channel under the deck.
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Re: What a drag!

Postby Roy Stuart » Sat Mar 24, 2012 10:18 am

Drag reduces the efficiency of fins and hulls rather than increasing it as suggested.
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Re: What a drag!

Postby mister-griffster » Sat Mar 24, 2012 12:37 pm

Theory and validation. If an experienced rider can feel the change in handling characteristics due to a singular change in board design from an identical one, and ridden in as similar waves as possible. Then that's scientifically good enough for me. How often this actually happens I'm not sure though.


I'd agree that this is the current method of validation on most 'theories' backed up by the principles of physics - but to my mind this is the exact problem and why so many surfers can 'claim' certain principles or charachteristics of their craft - it's not backed up by any reasonable observation... As we would all agree every wave is different - therefore how can there be a 'constant' required for the above - just because a surfer has switched a fin for example the only constant remains the board - everything else including the same rider is not a constant as there are too many chaotic factors to actually establish any definitive principle.

Interestingly most input comes from rider feedback which a shaper then interprets based on the principles that he understands. However, the theory has not been tested to it's fullest capacity - in an age where we have so many aids, interestingly very few shapers actually use these tools for measurement when it comes to their claims...

However, all that said - I'm still in the school of "FFS lets just go surfing" ;) - speaking of which.....
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Re: What a drag!

Postby mal-nourished » Sat Mar 24, 2012 1:16 pm

whats wrong with a bit of drag anyway how many times have we dragged our hand stalled and cutback to lose speed plennty and yes lets go surfing cooking down sunshine and offshore.
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Re: What a drag!

Postby kayu » Sat Mar 24, 2012 1:39 pm

Poostance , the deck venturi principal seems to periodically crop up every few years or so. I am not aware of it being used successfully so far. Hap Jacobs was the first "acknowledged " attempt , on a 10ft (?) Simmons around early 60's ......I'm yet to see the merrit , as I consider the constant change in displacing a board while riding it ( as in burying from one rail to the other) , kinda negates any advantage in the "air-cushion" effect......IMO , its more of a flat water high speed thing , which means it doesnt really do much for surfboards......
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Re: What a drag!

Postby kayu » Sat Mar 24, 2012 1:46 pm

mal-nourished wrote:whats wrong with a bit of drag anyway how many times have we dragged our hand stalled and cutback to lose speed plennty and yes lets go surfing cooking down sunshine and offshore.

I'm in agreement with that Mal !!!......an ounce of acceleration is worth a pound of speed in my book...
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Re: What a drag!

Postby Roy Stuart » Sat Mar 24, 2012 7:40 pm

mister-griffster wrote:
Theory and validation. If an experienced rider can feel the change in handling characteristics due to a singular change in board design from an identical one, and ridden in as similar waves as possible. Then that's scientifically good enough for me. How often this actually happens I'm not sure though.


I'd agree that this is the current method of validation on most 'theories' backed up by the principles of physics - but to my mind this is the exact problem and why so many surfers can 'claim' certain principles or charachteristics of their craft - it's not backed up by any reasonable observation... As we would all agree every wave is different - therefore how can there be a 'constant' required for the above - just because a surfer has switched a fin for example the only constant remains the board - everything else including the same rider is not a constant as there are too many chaotic factors to actually establish any definitive principle.

Interestingly most input comes from rider feedback which a shaper then interprets based on the principles that he understands. However, the theory has not been tested to it's fullest capacity - in an age where we have so many aids, interestingly very few shapers actually use these tools for measurement when it comes to their claims...

However, all that said - I'm still in the school of "FFS lets just go surfing" ;) - speaking of which.....


Humans are incredibly refined instrumernts which in some respects machines have never been able to match.

Regarding tubercules the difference is clearly noticeable and there has been a lot of scientific research into them as well.

This 'scientific validation' complaint is never invoked when mainstream industry shapers post the most arrant nonsensical pseudo scientific jabber ( like the venturi theory for example used to market bonzers, or 'bernoulli rails' as used by Tomo) nearly everyone just sucks it up.. it's really only wheeled out to question that which hasn't been picked up and promoted by the industry.... in reality most surfers are satisfied with industry marketing and acceptance as their validation and pretend in those cases that a few pseudo scientific terms bandied about shows scientific validation. Such people also have difficulty evaluating physics, so tend to rely on the Journal's prose instead.

:lol:
.
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Re: What a drag!

Postby Roy Stuart » Sat Mar 24, 2012 7:41 pm

mal-nourished wrote:whats wrong with a bit of drag anyway how many times have we dragged our hand stalled and cutback to lose speed plennty and yes lets go surfing cooking down sunshine and offshore.


It is useful to be able to apply drag when needed by dragging a hand for example but hull and fin drag is like having the brakes on permanently.
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Re: What a drag!

Postby Roy Stuart » Sat Mar 24, 2012 7:43 pm

kayu wrote:
mal-nourished wrote:whats wrong with a bit of drag anyway how many times have we dragged our hand stalled and cutback to lose speed plennty and yes lets go surfing cooking down sunshine and offshore.

I'm in agreement with that Mal !!!......an ounce of acceleration is worth a pound of speed in my book...


A non sequiteur... please try to keep up !

Regarding surfing speed one can't have it without acceleration, and one can't have acceleration without speed.
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Re: What a drag!

Postby kayu » Sun Mar 25, 2012 1:27 am

.....but one can certainly stall at will , then have acceleration on demand ..... 8).......speed does not produce acceleration ....acceleration produces speed !.......and waves do not change their behavior to suit surfboards.. 8)
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Re: What a drag!

Postby mister-griffster » Sun Mar 25, 2012 11:00 am

This 'scientific validation' complaint is never invoked when mainstream industry shapers post the most arrant nonsensical pseudo scientific jabber ( like the venturi theory for example used to market bonzers, or 'bernoulli rails' as used by Tomo) nearly everyone just sucks it up


That's exactly my point Roy - wouldn't it be nice for the mainstream to justify those claims via proper 'theory / testing / observation / analysis - after all, they're the cats with the kinda money that could set up some validation process.

In this case Roy I'm not saying that yourself, or anyone else on the forum should be the 'men in white coats' - I'm saying there's a lot of marketing BS / labelling / tags that accompanies claims made in the industry with no proper validation behind those claims. - Surfboard progression could move on leaps and bounds with rigorous testing.
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Re: What a drag!

Postby kayu » Sun Mar 25, 2012 12:20 pm

The ocean is the only test tank needed , and the surfing validates it........so its a matter of being aware of the BS , and paying no attention to it........quite a task for a green newby surfer , but knowledge comes with experience...... :!:
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