Can the quobba fin concept work 4 wsurf?

Watch video = quobbafins.com/

Hmmm. Interesting stuff Hards. I went and had a look at the website and it was intrigued by the concept. As per Ian's screenshot, I can see the inverted fillet section having an affect ( + or - I wonder) along the chord and aft, but what is creating the low pressure forward of the leading edge such that it projects so far foward? Are they modelling an enhanced leading edge zone of stagnation? I am wondering if the increased sensation if speed is instead due to the increase vertical lift (esp. from the mini horizontal foils), reducing the amount of board surface area contact?
It would be nice to see some scientific meat on the bones of this idea.

www.abc.net.au/news/2018-04-11/quobba-surfboard-fins-set-to-revolutionise-surfing/9641828

Sounds very gimmicky. how can you possibly generate a low pressure system in front of a fins direction of travel?

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Subsonic said..
Looking at the concept, maybe they think the fin with it particular shape is somehow going to "part the water" (pressure) before the fin arrives?

Maybe they could call it the "Moses" fin.

Haha! That's gold,
I wish I had a $2.5 million development budget.

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fangman said..

Subsonic said..
Looking at the concept, maybe they think the fin with it particular shape is somehow going to "part the water" (pressure) before the fin arrives?

Maybe they could call it the "Moses" fin.

Haha! That's gold,
I wish I had a $2.5 million development budget.

Maybe creates a micro foil action

A fin that draws you forward to make you go faster, Wow
Will be ideal for that wave park there going to build on the Swan river that's going to have 1000 perfect waves per hour

Looking at it it would cause a high pressure zone further back on the fin back by squashing the air between the little wing and the base of the board. I can only see it slowing you though as it would cause a fair amount of drag.

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Ian K said..

Had to bookmark that Sailquick! With explanation it's the best graph I've seen in donkey's.

Not sure exactly where to place the subject of this thread, To the right of the SFB?

Agreed Ian, defo to the right of SFB and creeping up to ZED.
I am still wondering what the $2.5 million was spent on. It can't all be marketing and beers in exotic locations can it?

Oh you doubting Thomas(es)....you do know these are designed on the physics of the flat earth model
BTW What's the rate of acceleration they claim as I'd like to know just how long it will take to reach light speed.

I guess the real question is are these fins any better or is it all just hype?

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Simon100 said..
I didn't really look into it but the explanation in the add sounds like they are trying to sell a perpetual motion machine. There's no free energy . No matter what magic you used to create a low pressure in front the energy is going to come from somewhere.

Is this serious? long term Seabreeze stalker just jumping on for a comment 'cause of a 'what the' moment (am too busy usually doing that sciency (inc. physics) type stuff)?

These are surfboard fins for surfing waves. What what would you call the energy from the wave? I'd call it free. What you're suggesting is the board sits on the surface of the water and propels itself forward by the fins ??

Aircraft fly because their engines force it forward through the air (i.e. the input of energy and definitely not free). It is kept in the air by lift. Lift is generated as air flows over the wings and an area of low pressure is created above the wing due to the flat foil shape compared to the pressure of the air flowing under the wing. This pressure differential causes 'lift' as (like water) air is always trying to equilibrate pressure so air (+wing) is 'sucked' towards the area of low pressure above the wing. This is aeronautics 101. If the engines aren't working, there is no forward movement and no lift generated.

It seems pretty obvious to me that the wave provides the forward motion like the engine does for the aircraft. As has been known with thruster side fins on shortboards for decades, a small amount of lift is created by turning the side fins in slightly (3 degrees or so toe from memory). These side flat foils which are shaped like a plane wing trade off a little bit of extra drag (by the fin being on an angle instead of straight) for a small amount of lift in an outward/slightly forward direction which as a net total provides a small amount of additional forward speed for the board thanks to the lift. This is well understood in the surfing and physics world and where they collide - i.e. not contentious or questionable. This is why just about every single three-fin shortboard for the past 4 decades has side fins arranged this way in the (hence named) 'thruster' arrangement.

I saw some fluid dynamics flow charts around one of these qobba fins on another page of this site and it seems to me that they have just managed to find a fin shape that generates more lift in a generally forward direction (through a larger lower pressure area created at the front of the fin due to the shape) than what is provided with the standard flat foil shaped side fins of a thruster set up that nearly every surfer uses every time they surf a wave.

Not magic. The science in fluid dynamics around a forward moving flat foil is well understood. They just appear to have a generated a better result from a different shape. Not surprising considering how little fin shape has been changed by FCS and Futures who sell 99% of surfboard fins. I don't have a spare 230 or I'd give them a crack at least on my surfboard. 2.5mill is quite of bit of $$ but there's 10s of millions of surfers on the planet, most with more than one board, so they only need a bit of the market to get their money back. More likely, the Aussie company sells to some cashed up buyer (cough..FCS..cough) and they retire on the sale.

I for one love new tech and the sciency stuff behind it. If it works, good luck to them. If it doesn't, the market will let them know.

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donut4u said..

As has been known with thruster side fins on shortboards for decades, a small amount of lift is created by turning the side fins in slightly (3 degrees or so toe from memory). These side flat foils which are shaped like a plane wing trade off a little bit of extra drag (by the fin being on an angle instead of straight) for a small amount of lift in an outward/slightly forward direction which as a net total provides a small amount of additional forward speed for the board thanks to the lift. This is well understood in the surfing and physics world and where they collide - i.e. not contentious or questionable. This is why just about every single three-fin shortboard for the past 4 decades has side fins arranged this way in the (hence named) 'thruster' arrangement.

Nonsense.

Most surfboards have a V bottom, double concaves, or similar underwater shapes. The water flow relative to the board is straight forward-backward only at the center line. Towards the side, the flow has an outward component, which is why fins mounted to the outside need to have a toe angle. The main reason to use thrusters is better grip in turns, not more lift when going in a straight line.

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boardsurfr said..

donut4u said..

As has been known with thruster side fins on shortboards for decades, a small amount of lift is created by turning the side fins in slightly (3 degrees or so toe from memory). These side flat foils which are shaped like a plane wing trade off a little bit of extra drag (by the fin being on an angle instead of straight) for a small amount of lift in an outward/slightly forward direction which as a net total provides a small amount of additional forward speed for the board thanks to the lift. This is well understood in the surfing and physics world and where they collide - i.e. not contentious or questionable. This is why just about every single three-fin shortboard for the past 4 decades has side fins arranged this way in the (hence named) 'thruster' arrangement.

Nonsense.

Most surfboards have a V bottom, double concaves, or similar underwater shapes. The water flow relative to the board is straight forward-backward only at the center line. Towards the side, the flow has an outward component, which is why fins mounted to the outside need to have a toe angle. The main reason to use thrusters is better grip in turns, not more lift when going in a straight line.

that is one reason but not the only one. As you will have read from my earlier cited articles, lift is created by the flat foil shape and the formation of low pressure above the foil creating a sucking effect which keeps aircraft in flight, hydrofoils lifting huge boats out of the water. What direction is the sucking effect (lift) directed towards when the angle of attack or toe is toward the stringer by 2.5 to 3.5 degrees? Bernoulli and Newton certainly don't say that it magically disappears.

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donut4u said..

What direction is the sucking effect (lift) directed towards when the angle of attack or toe is toward the stringer by 2.5 to 3.5 degrees?

Well there's a little bit of forward lift. For 3 degrees that equals the total lift generated by the fin times Sin 3 degrees. Sin 3 degrees = 0.05. Here we're assuming the fin is working on the angle of attack of the laterally spreading water under the board. 0.05 is 1/20th so your thruster fins need a lift to drag ratio of at least 20 to one to come out slightly ahead. Maybe they can at least be drag neutral if that angle of attack is carefully worked out? Which leads to another question. Are the two fins on either side of a quad fin board at different angles ? You'd expect the local flow angles vary all over the tail of a board? And is there twist in these fins to allow for the variation in spreading angle as you move deeper below the board?

Scavenging forward drive from the spreading wake before it pops out from under the board? Wishful thinking but does it disobey the laws of physics? Have to think about that.

The quobba fin is not all bad. At least it has got us thinking. ....About thrusters.

Could be an analogy with wingtip devices.

en.wikipedia.org/wiki/Wingtip_device
"Wingtip devices are intended to improve the efficiency of fixed-wing aircraft by reducing drag.[1] Although there are several types of wing tip device, which function in different manners, their intended effect is always to reduce an aircraft's drag by partial recovery of the tip vortex energy."

Whether you call it drag reaction, or partial recovery of tip vortex energy it all amounts to the same overall thing.

Not all planes have them so they must be hard to set up or have a limited range of moderate effectiveness. Only ever heard of thrusters being credited with extra grip in turns up until now.