# Funnelling as a form of channelling…

… as in so-and-so claims to have channelled with a dead relative.

Consider the funnel presented with a flow as sketched in the diagram.

The fluid flows, F volume per unit time, through the area A1 at the speed V1 = F/A1 (By the way, volume per unit time divided by area gives speed, which is of course, length per unit time.) Conservation of mass - though not universal like the law of conservation of energy, is found to be applicable for the kind of water flows generally observed in sports such as surfing, skiing, boating, etc. and, in this case demands that the same amount of fluid that enters the funnel also leaves it. Now, given the smaller area of the exit, this would require that the speed of the fluid leaving the funnel would have to increase relative to that at the entrance. In particular, V2, which is equal to F/A2, will be greater than V1, since A2 is smaller than A1, F being the same. In effect, you’ll have a created a jet, which you can then use to propel yourself(?).

Wow?

But wait, it gets better! You see the faster the water shoots out the back of the funnel, the faster you’ll go, and the faster you go, the faster the water will shoot out of the back of the funnel, and … well, maybe you get the picture. Heck, there’s no limit to the speed you could reach – watch out photons, here we come!

So build a funnel and put in under your surfboard, and just make sure you’re strapped in?

Gee, seems simple enough, how come nobody has come up this before? Well, they have, still do, and will likely continue to do so in the future. In fact, I met a fellow in the line-up the other day that had funnel fin on his board. He loved it and stood to do a good five minutes on why it worked… luckily, the sets were slightly more frequent.

But all that aside, is this possible, and if not, why not? In particular is it possible to put a funnel on the bottom of a surfboard and expect a little extra zip, or anything for that matter, as a result?

Here’s my answer, at least with regards to achieving some extra zip, no.

Here’s my reasoning. Whereas conservation of mass is definitely being obeyed, so is conservation of energy. The application of this latter principle becomes immediately clear (then again maybe not) when you realize that in order to hold the funnel in place you’ll need a force to do some work for you, in particular, you’ll have to change to momentum of the flowing fluid, which is just another way of saying you’ll need a force. In this case, such a force will appear as resistance, as in ‘resistance to motion.’ Heck, it’s not even a zero sum game. A lot of the work done on the fluid will take the form of heat and will simply be lost to the environment. In the end, the whole thing will tend to slow you down.

That’s not to say that the flow that’s there [under your board] can’t be tapped and used in creative ways, it’s just that there are constraints and basic physical principles [laws?] that must be considered, or you’ll wind up believe you’ve created the impossible – a perpetual motion machine – which you will not have done, because they don’t exist, at least they don’t appear to exist in this Universe.

But hey, perhaps I’m being a bit hard on ‘creativity’ – better to be objective and open-minded. So, please don’t let what I’ve written here stop you from sending whomever your easy payments of \$19.99 per month - hopefully you’ll let us know how it works out.

Next time “Fins that move out of the way.” or “The Joy of Crabbing.”

kc

Hi Kevin,

Nice post !

The ‘turbo tunnel fin’ has exactly the kind of constricted pipe which you drew, it’s a brake, like one of those ‘windsock’ sea anchors

Roy

Im no mathamatician but doesnt this neglect to consider drag created by water not entering the the opening of the funel and instead eddying around its outside edge? this might be more or eaqual drag than the drive/thrust the funnel creates? as the area of the funnel creating drag will be similar to that creating thrust?

rif.

indeed!

You want it scientifical, you get it scientifical :).

The same amount of mass that comes in at a time gets out at the same time. So the impulse remains the same.

There is now way to raise the impulse without external work (you need a sort of engine to do that).

Like Tom said, it will break!

rif,

I not that sure you’ve got to take it that far, leastwise I’m not going to.

But you seem to be suggesting a similar conclusion - it’s hoaky.

kc

Roy,

Three options come to mind:

1. Your Kuru has settled down (temporarily?).

2. That’s not you, as in someone else is using your account.

3. It is you.

I’m inclined to believe it’s either 1. or 2., but just in case it’s 3.

…thanks?

kc

Kevin my friend, it’s definitely me

1. Since I usually disagree with you I am acting out of character, however I don’t agree or disagree with someone because of their username, I do so on the basis of the content of the message, and since you made sense, I therefore agree with you.

2. That I am one of the venturi tunnel jet propulsion loonies because I use Vort-X tunnel fins, actually I’m not, we NEVER make the exit are on our tunnels smaller than the entry area, and have never postulated that they are perpetual motion machines. . . just highly efficient fins, that’s all

Have you noticed the constricted tube in the turbo tunnel ?

Cheers

roy

Back to the hydrodynamics of annular wings, what a lovely idea

Annular wings (tunnels) can have an efficiency advantage over equivalent flat plane wings, this can be expressed either as lower drag or higher lift.

Kevin was talking about the fact that constricting the flow inside the tunnel creates drag, and doesn’t ‘jet’ the board forwards by speeding up the water flow inside the tunnel, as many people like to believe.

A rough description of the goal is to generate lift as we pass through the water, while disturbing the water as little as possible .

.

Quote:

it’s a brake, like one of those ‘windsock’ sea anchors

Yeah exactly… otherwise if a boat put one of them in the water it would start to travel up-stream against the current… or accelerate towards the boat (if the boat was draggin it). They stop the water flow like a parachute…

rif.

!?

it makes no sence because it wouldnt/doesnt work.

rif.

I know. I edited/deleted my original response because there was actually a thread elsewhere that covered the subject, and I didn’t want to stir that up.

I either thought it was that or a revelation of some kind

Another analogy I thought of… place a funnel under a tap - turn the tap on - if the flow of water into the funnel increases it fills with water. If the water did actually speed up then it would drain itself.

but you soon realise the problem - it cannot drain itself faster than the water entering because there is a constant amount of water filling space. If it did drain faster than the water entering it would run out of water and create a vaccuum…

this is one I tried earlier…

HEY RiffRaff! Are you in HOUSTON?!

Quote:
Im no mathamatician but doesnt this neglect to consider drag created by water not entering the the opening of the funel and instead eddying around its outside edge? this might be more or eaqual drag than the drive/thrust the funnel creates? as the area of the funnel creating drag will be similar to that creating thrust?

rif.

Since water doesn’t compress you’d have to force feed it into the funnel, which is going to create resistance… or (and) as rif says, it will eddy around the opening.

If you’ve got something like a hose of a constant diameter containing the water until the funnel, that’s one thing… but if you’ve just got a bigger opening that funnels to a smaller opening, the added force required to get the water through a smaller hole will just act like a parachute.

Quote:

The ‘turbo tunnel fin’ has exactly the kind of constricted pipe which you drew, it’s a brake, like one of those ‘windsock’ sea anchors

The Turbo Tunnel opening is the same diameter from front to back. It may be a gimmicky thing, but Bob (the Greek) isn’t dumb enough to think you can compress water to gain speed. Several years ago Bob asked if I knew how he came up with the Turbo Tunnel. I said I didn’t. His answer - “it wasn’t patented”. After a few years of making and selling them he has changed the answer, and has all kinds of techno-babble to explain how it works. The first answer still sticks for me though. His prototype was made by wrapping a toilet paper tube with fiberglass and using that to split a fin. Where do you think he came up with the idea?

Does a Turbo Tunnel make your board perform better?

It sure makes Bob’s bank account perform better. That’s its primary function.

Quote:

The Turbo Tunnel opening is the same diameter from front to back.

`````` No it isn't, it is narrower at the exit, go and check some out with a ruler. . . . I did      An expensive mistake !     .
``````

I’ve had two Turbo Tunnels given to me by the Greek. One I gave away, and the other is on a board on long-term loan to Barry Hahn at the Surfing Heritage Foundation - he’s not riding it… it just lives in his garage.

The best review I can give is… I could set up my board to ride like it had a regular fin on it by pushing the Turbo Tunnel all the way forward in the box. I like minimal fins, so the TT seems like overkill. I love their tiny sidebites though. They’re so cute.

LOL!

You really think the greek came up with the idea on the… never mind…

I associated it with something else…

of course without the +/- 230 kn of Pratt and Whitney in the fin…

Well I can assure you that they have a constricted tunnel, exactly as drawn by Kevin above.

The constricted tunnel is one of three main design faults that the TT fin has.

Like I said, the fin is an expensive mistake.

Some of the early ‘Greek’ tunnel fins had a lot more potential, unfortunately he went for the tunnel on a stick instead of developing the hull mounted tunnel.

.