A taste of things to come...

[Roy Stewart]

"Roy Stuart crafts a singular surfboard" by Jacqueline Detwiler

http://olosurfer-woodensurfboardsatpipel...e-magazine.html

[jaffa1949]

I hope the board is featured in the business and first class magazine, as the board is first class and so is its price.
Off thread but; By the way did you ever get to read that book on The Forgotten Monarchy of Scotland

[behindThePeak]

how does a fin like that ride? how does it differ from the standard types?

[Roy Stewart]

Hi Jaffa, I'm sorry I don't recall you mentioning the book, I'm interested though is that the title ?

Behindthepeak the big tunnel fin is a unique experience, it has almost no rail to rail resisitance when turning, and provides lots of planing lift with very low drag, slick is the word which comes to mind.

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[Rickyroughneck]

Is it angled downwards in the middle to create lift, or is the surface curved at the top (the inside) to create lift like an aeroplane wing?

It looks like a smooth rail to rail experience at the cost of increased drag.

[jaffa1949]

Hi Jaffa, I'm sorry I don't recall you mentioning the book, I'm interested though is that the title ?
.

Morning Roy. yes that's the title both my father and I found it an interesting read if Kings are your thing and on the RS site you said they were one thing so have a look.

[Roy Stewart]

Is it angled downwards in the middle to create lift, or is the surface curved at the top (the inside) to create lift like an aeroplane wing?

It looks like a smooth rail to rail experience at the cost of increased drag.

Hi Ricky

Firstly it doesn't need to be curved on the inside in order to create lift ( we do them both ways, the chieftain fin is curved or foiled on the inside )

Secondly the fin wil create lift even if it is has the same angle of attack as the surfboard bottom in the fin area, in that case it acts as a slave foil.

Regarding drag a lot of fin drag is caused by the fin tip, the tunnel doesn't have one and it's a low drag fin. Keep in mind also that the horizontal fin area provides planing lift at a better lift drag ratio than the hull has, so it can reduce overall surfboard drag.

The tunnel finned boards are very fast, which is evidence of a good lift/drag ratio.

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[Rickyroughneck]

Thanks for the reply. Does that mean there is turbulence on the inside of the tunnel sucking it up? That is a very interesting because just passing a plane underwater creates no lift as the forces are the same top and bottom, so there must be something generating this perceived speed.

I am surprised that there have been no fin-tip modifications made yet. Having a ^ shape attached to bottom of the fin could probably reduce drag in a similar way to winglets. Perhaps that might be something to investigate?

[billie_morini]

Roy,
thanks for sharing this with us. You make such pretty things.

Here is a funny little thing: The price shown on the provided link is "$417,000." Due to how commas and decimals (points) are used in the USA, this price would be interpreted as "four hundred and seventeen thousand dollars."

Tschüs,
Billie

[Roy Stewart]

Roy,
thanks for sharing this with us. You make such pretty things.

Here is a funny little thing: The price shown on the provided link is "$417,000." Due to how commas and decimals (points) are used in the USA, this price would be interpreted as "four hundred and seventeen thousand dollars."

Tschüs,
Billie

Hi Billie, that is indeed the correct price.

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[Roy Stewart]

Thanks for the reply. Does that mean there is turbulence on the inside of the tunnel sucking it up?

That is a very interesting because just passing a plane underwater creates no lift as the forces are the same top and bottom, so there must be something generating this perceived speed.

That's not correct. A flat plane moving underwater will generate lift as soon as it is presented at an angle of attack to the water flow. Even a wing which is curved underneath and flat on top will produce lift.

You are possibly subscribing to a common misinterpretation of Bernoulli's theory. In fact Bernoulli's theory and Newtonian physics explain lift, they give the same answer, namely that a flat plate will create lift.

The simplest way to visualise a tunnel fin is as a water redirection unit, it creates lift by redirecting water flow up, down, or sideways.

I am surprised that there have been no fin-tip modifications made yet. Having a ^ shape attached to bottom of the fin could probably reduce drag in a similar way to winglets. Perhaps that might be something to investigate?

The planshape for a planar fin which produces the least tip turbulence is the elliptical 'spitfire' shape. Winglets on the tip have been used, I avoid them these days as they tend to create handling problems.

[billie_morini]

Thanks, Roy. Just goes to show I'm so far out of your league that I am clueless.
Billie

[Roy Stewart]

Hi Billie, hyper expensive boards are new territory for everyone including myself !

[jaffa1949]

Just one sale Roy, just one, then watch the faces of all the detractors ( should be worth while just for the inward pucker they will undergo).

[Roy Stewart]

Ah the old inward pucker, can't wait.

Then there's the eating of hats and crunching of words.

[jaffa1949]

Ah the old inward pucker, can't wait.

Then there's the eating of hats and crunching of words.

Probably worth more to you than the $$$$$

[Rickyroughneck]

The planshape for a planar fin which produces the least tip turbulence is the elliptical 'spitfire' shape. Winglets on the tip have been used, I avoid them these days as they tend to create handling problems.

Yeah I imagined that might be the case. Shame

That's not correct. A flat plane moving underwater will generate lift as soon as it is presented at an angle of attack to the water flow. Even a wing which is curved underneath and flat on top will produce lift.

You are possibly subscribing to a common misinterpretation of Bernoulli's theory. In fact Bernoulli's theory and Newtonian physics explain lift, they give the same answer, namely that a flat plate will create lift.

The simplest way to visualise a tunnel fin is as a water redirection unit, it creates lift by redirecting water flow up, down, or sideways.

Yes, but that is the same way that the surfboard hull creates lift, and assuming the same angle of attack it will present no lift-drag advantage. In fact it may present a disadvantage due to the larger frontal surface area (which provides no lift, only drag).

Additionally, if it is presented at an angle steep enough to create turbulence above it (such as when delta wing aircraft come into land, many cool videos!), there will be additional sucking lift, but not enough upwards force to outweigh the vastly increased drag of the system.

Lastly, the position of the fin on the board is at the rear, where the hull faces downwards (due to rocker), or close to horizontal depending on rider positioning. Do you alter the angle of attack of the fin to compensate?


The only way I could see a tunnel fin providing any advantage, is if the angle of attack provides a superior lift-drag ratio than the hull of the surfboard. That would be dependant on exact rider positioning so it is hard to imagine that working in a real life scenario, although that is not to say it is impossible.

[Roy Stewart]

The planshape for a planar fin which produces the least tip turbulence is the elliptical 'spitfire' shape. Winglets on the tip have been used, I avoid them these days as they tend to create handling problems.

Yeah I imagined that might be the case. Shame

That's not correct. A flat plane moving underwater will generate lift as soon as it is presented at an angle of attack to the water flow. Even a wing which is curved underneath and flat on top will produce lift.

You are possibly subscribing to a common misinterpretation of Bernoulli's theory. In fact Bernoulli's theory and Newtonian physics explain lift, they give the same answer, namely that a flat plate will create lift.

The simplest way to visualise a tunnel fin is as a water redirection unit, it creates lift by redirecting water flow up, down, or sideways.

Yes, but that is the same way that the surfboard hull creates lift, and assuming the same angle of attack it will present no lift-drag advantage.

That's an incorrect assumption, and you don't say what it's based on.

Additionally, if it is presented at an angle steep enough to create turbulence above it (such as when delta wing aircraft come into land, many cool videos!), there will be additional sucking lift, but not enough upwards force to outweigh the vastly increased drag of the system.

You still seem to be using a misinterpretation of Bernoulli's theory.

In addition you keep arbitrarily and incorrectly stating that the fin has reduces the lift/drag ratio of the system.

In other words you are talking nonsense !

Lastly, the position of the fin on the board is at the rear, where the hull faces downwards (due to rocker), or close to horizontal depending on rider positioning. Do you alter the angle of attack of the fin to compensate?

Angle of attack is relative to the direction of water flow, so in fact the 'faces downwards' notion is incorrect.

The only way I could see a tunnel fin providing any advantage, is if the angle of attack provides a superior lift-drag ratio than the hull of the surfboard.

https://surfing-waves.com/forum/posting.php?mode=quote&f=15&p=144960#

Firstly the tunnel provides a big advantage.

Secondly it is not the angle of attack which provides a lift drag ratio an angle of attack is required but it is the fin characteristics which determine the lift drag ratio.

That would be dependant on exact rider positioning so it is hard to imagine that working in a real life scenario, although that is not to say it is impossible.

It does not depend upon 'exact rider positioning' and it works in 'real life scenarios'

Unfortunately your understanding of the physics involved is very poor.

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[Roy Stewart]

By the way the difference which the tunnels make is incredible !

I can explain in detail but you'll first have to realise that you don't know what you are talking about.

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[Rickyroughneck]

By the way the difference which the tunnels make is incredible !

I can explain in detail but you'll first have to realise that you don't know what you are talking about.

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It is easy to say "you don't know what you are talking about", but you have yet to provide evidence that I am wrong.

In fact Bernoulli's theory and Newtonian physics explain lift, they give the same answer, namely that a flat plate will create lift.

A flat plate moving underwater creates no lift unless there is an angle of attack, as above. It is bad science to mention only half of a theory to support an idea. If it moves while facing horizontally, there is no lift as the forces are identical top and bottom (gravity and buoyancy ignored).

There are two types of lift, the first is that which is created by an angled fin (or the hull of the surfboard) physically pushing the water down as it moves through it. Whether it is a fin or the board, the mechanic of lift is the same, Newtons 3rd all over again.

The second is the sucking lift generated by bernoulli's principle, which requires a foiled upper half of the fin. That is the same principle of suction force that is created by turbulence, which occurs when the angle of attack of the fin is great enough. I think you may have misunderstood the principle yourself.

Angle of attack is relative to the direction of water flow, so in fact the 'faces downwards' notion is incorrect.

Yes my bad , I didn't take into account the change in direction of the water flow exerted by the board. Sorry!

Secondly it is not the angle of attack which provides a lift drag ratio an angle of attack is required but it is the fin characteristics which determine the lift drag ratio.

Fin characteristics is bull, I am sorry if this offends you. You can divide the tunnel fin into a vertical and a horizontal component (of which the latter can be ignored). The mechanics of lift would be the same as if the fin was square, v or any non-vertical angle (assuming all parts of the fin point the same way). What I mean by the pointing the same way, is that if the fin is infinitely thin, perspective ignored, you would not see it from the front (or back).

Also, there is an optimum angle of attack with regards to lift-drag. There is a lot of scientific literature to support this. It is also extremely relevant since (as you stated), lift from the fin would reduce drag on the hull as it is higher in the water.


I would like you to explain in detail please, because at the moment the burden of proof lies with you. It is no use throwing out the names of a few well known principles unless you actually back it up by saying HOW it relates to what you are saying. At the moment it is all talk without the punch, so to speak.