The Spoon trick

Swissrigger · Oct 11, 2006

""This spoon experiment demonstrates the Bernoulli Principle.

This is what the bottom of a "rounded" riding surface does when you try to turn a boat.

This is what causes a hydro to "nose steer".a tunnel boat to "hook" and a mono to "spin out".

Just very lightly hold the spoon between your fingers and feel how the spoon is drawn into the water stream.""

Rod,

Really interesting thread. To my opinion things are more complex.

Bernoulli principle is OK but I think you should also consider the Coanda effect looking on water flow on curved surfaces.

In Wikipedia (http://en.wikipedia.org/wiki/Coanda_effect) they describe it:

The Coandă effect, also known as "boundary layer attachment", is the tendency of a stream of fluid to stay attached to a convex surface, rather than follow a straight line in its original direction. The principle was named after Romanian inventor Henri Coandă, who was the first to understand the practical importance of the phenomenon for aircraft development. He made the discovery during experiments with his Coandă-1910 aircraft, which is the first aircraft based on an early type of jet engine.

You will find in this link also a picture of water flow on a spoon.

Looking on riggers and possibly tunnels the "Ground Effect" should be considered also. You will find a nice description in:

http://en.wikipedia.org/wiki/Ground_effect and

http://www.mh-aerotools.de/airfoils/javafoil.htm

Kind regards,

Petr

PHM Racing · Oct 11, 2006

Rod i have been following this thread from the begining and when my wife seen me with the spoon rinsing as she called it and told me she was very happy that i was doing the dishes for her.

My point is i can't get out of doing the dishes so you can't get out of teaching us more.

Just ignore the smart a$$es and go on with the people that are listening and absorbibg the info.

If teacher's were to walk out of class room's when the got upset we all would be DUMB A$$ES.

Anyway i have dishpan hand's so it's hard to type so i hope you come back on.

Thanks

Wesleys Custom RC · Oct 11, 2006

PHM Racing said:
Rod i have been following this thread from the begining and when my wife seen me with the spoon rinsing as she called it and told me she was very happy that i was doing the dishes for her.

My point is i can't get out of doing the dishes so you can't get out of teaching us more.

Just ignore the smart a$$es and go on with the people that are listening and absorbibg the info.

If teacher's were to walk out of class room's when the got upset we all would be DUMB A$$ES.

Anyway i have dishpan hand's so it's hard to type so i hope you come back on.

Thanks

OK , I'm going home to try this spoon thing before my wife gets home!!!.......... see, I'm learning !

Charles Perdue · Oct 11, 2006

Mr. Geraghty, if you are referring to me, believe me, I meant no disrespect. I am a fan of yours. I thought that the discussion was going ok considering the way some of them have gone lately. Thanks for the contributions. Don't give up on us DUMMIES now.

Rich Z · Oct 11, 2006

Rod,

Really interesting thread. To my opinion things are more complex.

Bernoulli principle is OK but I think you should also consider the Coanda effect looking on water flow on curved surfaces.

In Wikipedia (http://en.wikipedia.org/wiki/Coanda_effect) they describe it:

The Coandă effect, also known as "boundary layer attachment", is the tendency of a stream of fluid to stay attached to a convex surface, rather than follow a straight line in its original direction. The principle was named after Romanian inventor Henri Coandă, who was the first to understand the practical importance of the phenomenon for aircraft development. He made the discovery during experiments with his Coandă-1910 aircraft, which is the first aircraft based on an early type of jet engine.

You will find in this link also a picture of water flow on a spoon.

Hey Rod!

Please, I hope you are not offended by my qoute which also was copied from Wikipedia. I agree with you 100%. You were just barking up the wrong "principle". I can get a bit obtuse from time to time. BTW I still think your gas blender in the best idea yet - I have been in this hobby longer than a lot of you guys have been alive - seen a lot of ideas come, go, work, not work. Must admit you have a handle on things.

Rich

dr gary turner · Oct 11, 2006

Geraghty said:
This spoon experiment demonstrates the Bernoulli Principle.

This is what the bottom of a "rounded" riding surface does when you try to turn a boat.

This is what causes a hydro to "nose steer".a tunnel boat to "hook" and a mono to "spin out".

Just very lightly hold the spoon between your fingers and feel how the spoon is drawn into the water stream.

Rod, It is also what stops a nose up when patients "sniff" all of the time. Bernoulli was quite a guy. His principal affects a lot of things. Gary

Propjockey · Oct 12, 2006

Hmmmm........?

Light bulb going off!

Am I getting close?

twox45 · Oct 12, 2006

I have been working with Rod on this spoon thing since 96. It made a believer out of me. Our goal is to eliminate the negative pressure area created by curved surfaces on the bottom of our boats.

One of the most obvious examples of this, for me, was a 90 Youngblood mono. For any of you who have been lucky enough to run one of these beast, I am sure you seen the problem. This thing would scream down the straights but don’t dare give it any right rudder. Just as soon as it rolled to the right and the bow made contact with the water the back of the boat would fly around and the boat would scoot backwards for about 50 feet. It was so bad Bob Kernodle named it “Scooter”. When it would slow down enough the back of the boat would set back down in the water and it was off to the races again. After many hours of trials and tribulations I decided that the only way to get the boat to turn was to just slow down. I was at the 96 Nats running it during open water and I didn’t slow down enough and it did the Scoot. After I brought it back to the bank Rod walked up and said “I think I can help you with that”. He explained that as the bow would set in the corner the water was traveling up the side of the boat and pulling it under. I was a little skeptical, because I just knew the problem was in the back of the boat. He took an 1/8” square x 12” long strip of balsa and glued it on starting at the point of the bow and ran it along the side. Without making any other adjustments we cranked it up and threw it out. I nailed it down the back straight and tried my best to make it Scoot. But to my surprise the boat turned. I cut 5 & 6 but I had it under control. I dialed a little rudder out and the thing ran great. It ran so well we were in first place going in to the 5th round of the heat racing portion of F mono. But as most good things this had to end, we broke a crank in the 5th heat.

The point I am trying to make is moving arced / curved surfaces and water don’t work well together if you are trying to stay above the surface. By adding the strip of balsa it broke the flow of water and eliminated the low pressure area.

The one thing that all the physicist agree on is that as fluid, weather it is air or water, passes over a curved surface it accelerates and creates a lower pressure. This low pressure effect is not limited to just air and wings. The effect water has is much more drastic because water is more dense than air. One example is Rods plastic spoon. Another example is your garden hose, if you adjust the nozzle to a smooth steady stream and put your relaxed index finger parallel with the flow it will actually pull it into the stream.

If you can actually feel the effect on something as small as a plastic spoon imagine the effect it would have on the arced portion of your hydro tub as its trying to get on step. Or the effect it would have on the front of your sponsons and tub at speed in rough water. The same with tunnels and monos.

David Hall

Mike Hughes · Oct 12, 2006

Ding, ding, ding. Give that man a prize.

Chris Thomas · Oct 12, 2006

I think there is some confusion between applying Bernoulli principle vs. the "spoon" application. Increase the speed of the fluid going past the convex surface of the spoon, it will decrease. Surface tension (of the water) will make the water "adhere" to the spoon. I don't think this is the right application for the Bernoulli equation, since fluids are at a constant pressure.

Geraghty · Oct 12, 2006

Mike,Tom

Since I was the sponsor of this thread,I would like to have one of you kill it where it stands.

If somebody wants to start this up again under their sponsorship,be my guest.

If somebody out there has a desire to discuss how to stop boats from doing stupid things,I would be glad to talk to you on the phone.Give me your full name and number and I will be glad to call you.

Rod Geraghty

Terry Keeley · Oct 12, 2006

I know I'm building a new set of front shoes this winter...

Preston_Hall · Oct 12, 2006

fluids are at a constant pressure

Give me a minute why I call my old physics teacher and tell him not to worry with a pressure differential because obviously there is none. How can you possibly say that if a fluid is moving over a curved suface?

If the pressure was all the same then the boat would never fly off the water as the top and bottom pressures would be the same. Besides that, the boat would not go anywhere because everything moves because of pressure differentials.

At any rate, I saw a fellow increase the "belly" (which is the low pressure area) beneath his 1/8 scale to help it hold the water. Obviously Bernoulli and Rod are correct.

John Finch · Oct 13, 2006

Rod, Sorry to not kill it right here. I am glad that you are willing to share your knowledge. Not everyone wants to hear it, but I believe the majority look up to you and you advice. To back you up I will tell a story not to many people know. Don Ferrette and I were attempting to break the 40 hydro oval record a couple of years ago and could not get control of his sgx 20 hull. After many poor attempts at getting control of the boat I installed a pair of sponsons I had build special for the boat. They have belly where the original sponsons do not. When we had control of the boat we borrowed a tuned pipe from Preston and blew the record away by several mph. When we got the time we thought would stand for a while we stopped. The boat is still intact. That same boat is going to straightaway trials next month, but with stock sponsons. No belly. Hint Hint. Sometimes sponsons that suck are ok.

Wesleys Custom RC · Oct 13, 2006

Geraghty said:
Mike,Tom

Since I was the sponsor of this thread,I would like to have one of you kill it where it stands.

If somebody wants to start this up again under their sponsorship,be my guest.

If somebody out there has a desire to discuss how to stop boats from doing stupid things,I would be glad to talk to you on the phone.Give me your full name and number and I will be glad to call you.

Rod Geraghty

DON'T LEAVE SO FAST! I've got questions. I was up at 3 this morning thinking about this crap. Be gentle on me, I'm a simple man and I have to look at things in simple terms before I can apply them. Someone stated that the Bernoulli principle applies to air as well. If that is the case then why does a cupped rock or upside down sea shell "skip " accross the water and not get sucked in? Or better yet, take an floatie or inner tube with a bottom (basically a spoon shape) and pull it behind a boat. At low speeds the raft or "spoon" gets sucked down (Bernoulli principle) but as the boat speeds up the raft exerts less drag not more as you would summize from Bernoulli. Increase speeds more and you are on funniest home videos. My question is this: as speed is increased does the Bernoulli effect decrease or are there other factors increasing their effect ( like ground effect) also, does the Bernoulli effect reallt work in air or is it just less efictive than gravity, ground effect, airo dynamics etc.???? :blink:

Chris Thomas · Oct 13, 2006

OK i'm confused. Why wouldn't the water underneath a sponson displace the air (pressure) above the form. Seems more likely to want to float (ride on) than be drawn into the water?

Not to add more to the mix: would this also be a side effect of placement of the pressure tap in a tuned pipe? Speed vs. pressure differential.

izitbrokeyet? · Nov 22, 2006

Geraghty said:
m larson said:

m larson said:

Hey Rod! According to Bournelli, then the problem with my WOF hooking is a possible rocker situation with the sponsons? They sit bone dead flat on the table with razor sharp edges where the sides join with the bottom...... its the non trip in question to me, with a definite edge there,( an edge, I intend to round off) causing a trip situation upon entering the turn. Or not. The faster you run the water the harder the spoon sucks into it, what, if the blow off prone tunnel hull, would be wrong, in building a semicircular hull,( exaggerated) if the faster it goes the harder the "effect" holds the hull to the water? Problem, being with finding the point that the effect is lost, and lift off commences.... In theory, or not, at least with my spoon, faster water meant more pull..... Now, theory, and completely as so, what, and you and tommy may have tried, would happen to a build, if, said builder made the surfaces "S" shaped to countereffect the effect fore and aft? Say, down ( reverse spoon) at the rear, and up at the front ( normal spoon) Or vice versa...... To me the hulls balance as if on a fulcrum, so, it would seem logical, to build the reverse and normal the same, all else being equal, to start? Finding the point of the normal, and reverse lift built into the boat would seem a task worth looking into, its just plywood and foam, right? OR not...... In my judgement, as these hulls reach the maximum speed by design each one is unique to, lift off occurs and you have, in effect, compromised bournelli, just like a plane does upon reaching its speed upon takeoff....... Ramblings from an *****, possibly, Searching for the tunnel answer, always..... I know you dont like to type, take it as you will, I do appeciate the brain strain.... mike

Click to expand...

What in the hell did I do to deserve all this??????? :huh:

Lets start by spelling Bernoulli correctly.

1.Mike,unless your sponsons are dead flat from their tips to their tails......they are "not" dead flat.

2.Hydrodynamics and aerodynamics are two different subjects in the design of a tunnel hull.

Trust me,the spoon experiment tells it all.

Mike,you just keep rounding off all your edges and build some "S" shaped sponsons and enjoy your extended afternoons you are going to spend in the chase boat.

Click to expand...

izitbrokeyet? · Nov 22, 2006

Rod you should call me,

I thought Rangers led the way.........I'll post again next week.

Happy Thanksgiving!

Please remember to give thanks to all you love, our time together is limited! and our reasons to give thanks are so so many!

KB

Dan Hydro · Nov 22, 2006

izitbrokeyet? said:
Rod you should call me,

I thought R*****s led the way.........I'll post again on December 1st. (or therabouts)

Happy Thanksgiving!

Please remember to give thanks to all you love, our time together is limited! and our reasons to give thanks are so so many!

KB

Guys, although I have studied the principle I will not put an other explanation. The answer was already given in post #48. Just keep in mind that there is something else on your boat that helps or have an effect towards the principle. Don't over think it or over analyze it, keep it simple, think outside the box.

Mark Poole ModVP · Nov 23, 2006

Well I have to give credit where it is due. I recently solved a little cornering problem my boats had. Thinking about what Rod explained in this thread is what led me to making the improvement. Rod and Tommy may not be building and racing boats now but thanks to them sharing what they know my product has been improved. Rod, some of us will listen and think. This computer is an information superhighway. Just ignore the junk on the road.

Mark

The Spoon trick

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