Experiment #1

[Wally Marsh]

Hey tunnel junkies,

This discussion is what this type of news goup is all about. Despite my headache from y'all making me think too hard, it has been both fun and extremely educational. I by no means rank myself up there with the tunneboat "kingpins" but must admit after spending gobs of hours over several years of experimenting with my XTR-21 and Villian S1 I am beginning to learn a few things, both from suggestions and from my own school of hard knocks AND DOCUMENTING EVERTHING THAT HAPPENS. The old girl finally met her demise with an immovable object last fall, so I get to start all over again with a new hull design, but it'll be a blast. Thanks to the likes of Rod, Mike, Gene, Tom, Charley, etc. for stimulating this discussion.

Just had to belch out my 2 cents worth and see y'all next season. h34r:

the Wallster

 

[Speedway]

"Hint:Atmospheric pressure on the concave surface of the spoon is "pushing" the spoon into the water stream."

The only atmospheric pressure here is what your exuding! Unless your using the Jedi thinking patterns where "what is not, allows to be, Jedi master". I remember that experimement from grade 10 Science and it was on Adhesion/friction etc.etc. I'll wrap it up in a nutshell. DIMPLE the bottom of the sponsons and off you go.

 

[Wally Marsh]

Yep, just like "sucking" through a straw. You're not sucking anything, just creating a low pressure zone at the top and atmospheric pressure takes over driving the liquid through the straw. There, now you all know my entire knowledge of science, just don't tell my employer!

What I REALLY want to know is why are we (NASA) sending off a rocket to blast a crater/hole into a comet. :blink: Knock that thing out of it's orbit who knows what'll hgappen :huh:

Wallster

 

[Speedway]

My Money's on Finding Hoffa's final resting place

Yep, just like "sucking" through a straw. You're not sucking anything, just creating a low pressure zone at the top and atmospheric pressure takes over driving the liquid through the straw. There, now you all know my entire knowledge of science, just don't tell my employer!
What I REALLY want to know is why are we (NASA) sending off a rocket to blast a crater/hole into a comet.  :blink:   Knock that thing out of it's orbit who knows what'll hgappen  :huh:

Wallster

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[Watercadet]

"Hint:Atmospheric pressure on the concave surface of the spoon is "pushing" the spoon into the water stream."
  The only atmospheric pressure here is what your exuding!  Unless your using the Jedi thinking patterns where "what is not, allows to be, Jedi master".  I remember that experimement from grade 10 Science and it was on Adhesion/friction etc.etc.    I'll wrap it up in a nutshell.  DIMPLE the bottom of the sponsons and off you go.

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OK one of us missed what Rod said. I believe he was refering to the spoon experiment where the convex side of the spoon was placed into the stream of water and the spoon was not sucked into the water, but rather pushed in by atmospheric pressure on the concave side of the spoon. So control is being gained by atmospheric pressure not water contact?? How do I smell Rod?

Adam

 

[Watercadet]

has anyone tried a tunnel with an upside down airfoil section? I suggested that a while back.

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Yes we have.[Tommy and I,several times]It doesn't work.

You will have the most evil porpoising tunnel boat on the planet.

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Do the rules allow a "vented" type of center section like the two wing Unlimited hulls?

Adam

P.S. This thread is awesome Rod! I have all kinds of juices flowing...don't know what kind of juices but it feels good!! When this dies down please continue with the experiments.

 

[Speedway]

But that would be incorrect. He may be using it to Illustrate the effect, but its the wrong example if he's trying to show any form of atmospheric pressure. He might has well have invited you to fart in a pickle jar and check for effects of turbulence. I think he's getting at the Dimple. A golf ball with no dimple flies on average of 10-17 percent slower than one with dimples. The dimples offer a concave area to accelerate a force (wind or water). Try the Jar

"Hint:Atmospheric pressure on the concave surface of the spoon is "pushing" the spoon into the water stream."
  The only atmospheric pressure here is what your exuding!  Unless your using the Jedi thinking patterns where "what is not, allows to be, Jedi master".   I remember that experimement from grade 10 Science and it was on Adhesion/friction etc.etc.    I'll wrap it up in a nutshell.  DIMPLE the bottom of the sponsons and off you go.

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OK one of us missed what Rod said. I believe he was refering to the spoon experiment where the convex side of the spoon was placed into the stream of water and the spoon was not sucked into the water, but rather pushed in by atmospheric pressure on the concave side of the spoon. So control is being gained by atmospheric pressure not water contact?? How do I smell Rod?

Adam

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[Watercadet]

But that would be incorrect.  He may be using it to Illustrate the effect, but its the wrong example if he's trying to show any form of atmospheric pressure.  He might has well have invited you to  fart in a pickle jar and check for effects of turbulence.    I think he's getting at the Dimple.  A golf ball with no dimple flies on average of 10-17 percent slower than one with dimples.  The dimples offer a concave area to accelerate a force (wind or water).      Try the Jar

"Hint:Atmospheric pressure on the concave surface of the spoon is "pushing" the spoon into the water stream."
  The only atmospheric pressure here is what your exuding!  Unless your using the Jedi thinking patterns where "what is not, allows to be, Jedi master".   I remember that experimement from grade 10 Science and it was on Adhesion/friction etc.etc.    I'll wrap it up in a nutshell.  DIMPLE the bottom of the sponsons and off you go.

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OK one of us missed what Rod said. I believe he was refering to the spoon experiment where the convex side of the spoon was placed into the stream of water and the spoon was not sucked into the water, but rather pushed in by atmospheric pressure on the concave side of the spoon. So control is being gained by atmospheric pressure not water contact?? How do I smell Rod?

Adam

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Well tryed the farting into the pickle jar and the mix of left over pickle juice and my own methane levt me on the floor. Forget studying turbulence. You jackass Canuck

Adam

 

[Speedway]

Hey,, Even a Jackass Canuk woundnt try the Pickle Jar. Keep us posted on your results

But that would be incorrect.   He may be using it to Illustrate the effect, but its the wrong example if he's trying to show any form of atmospheric pressure.   He might has well have invited you to  fart in a pickle jar and check for effects of turbulence.    I think he's getting at the Dimple.  A golf ball with no dimple flies on average of 10-17 percent slower than one with dimples.  The dimples offer a concave area to accelerate a force (wind or water).      Try the Jar

"Hint:Atmospheric pressure on the concave surface of the spoon is "pushing" the spoon into the water stream."
  The only atmospheric pressure here is what your exuding!  Unless your using the Jedi thinking patterns where "what is not, allows to be, Jedi master".   I remember that experimement from grade 10 Science and it was on Adhesion/friction etc.etc.    I'll wrap it up in a nutshell.  DIMPLE the bottom of the sponsons and off you go.

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OK one of us missed what Rod said. I believe he was refering to the spoon experiment where the convex side of the spoon was placed into the stream of water and the spoon was not sucked into the water, but rather pushed in by atmospheric pressure on the concave side of the spoon. So control is being gained by atmospheric pressure not water contact?? How do I smell Rod?

Adam

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81082[/snapback]

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Well tryed the farting into the pickle jar and the mix of left over pickle juice and my own methane levt me on the floor. Forget studying turbulence. You jackass Canuck

Adam

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[Tommy Lee]

Well- as I read this I have to say something and I don"t care who gets P---ed off. Most of you younger guys weren't around in the mid to late 70's when there were several tunnels for sale to the public but you cannot believe how slow they were, how bad they handled and how hard they were to drive. In the early 80's Rod Geraghty came upon the concept of what I will call the modern-era tunnel hull i,e- shorter flat running surfaces and front sponsons, yes I said sponsons because that is what they are not stumble blocks.(the ones stumbling are the people trying to run without them.) After a year of phone calls and sending photos and drawings back and forth Rod and I came up with the XT-460 which is by far the best tunnel to ever hit the water for the average boater. This boat has won more races and National Championships than all the other brands combined. And is still winning today after 20 years. However, this is not a commercial, the point is that there have been NO significant changes in 20 years. The Aerotech,Hopper,Tri-star,Villian,Lynx and 10 other models out there were all copies or should I say direct descendants of this boat. Yes there have been minor changes but all of these boats are built around the "Geraghty"concept. So the bottom line is LISTEN- Rod is trying to get builders to think about why the boats do what they do and how to change them. I have built at least 25 boats that no one ever saw in the water except me. Some worked and some didn't and that is how you get there. You have to want it bad enough to find it.

 

[Jerry Dunlap]

re: stumble blocks/front sponsons

Hey Tommy Lee!!! Blame Geraghty for the term "stumble blocks," hell blame Geraghty for all the problems in the world!! Personally, I like "stumble blocks" because it rather accurately describes what the devices prevent.

JD

 

[Dale0]

Rod, I think what your trying to show is that the spoon is sucked into the stream. So if the bottom of a boat, or chine is shaped like a spoon its going to suck down into the water. I think thats what makes tunnels hook. You told my father (Dick Roberts) about this experiment about 20 yrs ago, and i have never forgotten it.

 

[jayt]

You told my father (Dick Roberts) about this experiment about 20 yrs ago, and i have never forgotten it.

It's a lot older than that. I remember reading it in an early '70s construction article in RCM by Dick Hansen. Don't know where Dick got it....but it has stuck with me for over 30 years.

 

[Geraghty]

"Hint:Atmospheric pressure on the concave surface of the spoon is "pushing" the spoon into the water stream."
  The only atmospheric pressure here is what your exuding!  Unless your using the Jedi thinking patterns where "what is not, allows to be, Jedi master".  I remember that experimement from grade 10 Science and it was on Adhesion/friction etc.etc.    I'll wrap it up in a nutshell.  DIMPLE the bottom of the sponsons and off you go.

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You missed something in your 10 grade science class.

This experiment has nothing to do with aerodynamic surface friction.

The atmospheric pressure i am eluding to is pushing on the spoon,not flowing over it.

 

[Slideblues]

Hi Tommy,

Great to see ya here posting again, Please chime in on any of my posts, Or any tunnel post for that matter, I like to hear you opnions on stuff

Ok Rod, a "BIG" lite bulb just went on with me, (large fillet where the cowl meets the deck) will keep the boat from blowing off, Did I read that one right ? like Tommys XTR21

Gene

 

[Duck899]

Guys,
You all are a little wet!  :huh:   I watch different  tunnel hulls run in the .21 outboard class, wood, fiber glass, wof, etc it does not matter. Then I watch my Lynx run HUMMMMMMMM.......... Looks like someone did some homework. Even better listen to the motors on the .21 tunnels then listen to a Lynx's tunnel motor....   More RPM's are noticable!!  

Where is it written that all tunnels have to follow actual Formula 1 designs?  Remember you can't scale up water, wind, or air.  They are all constants!!

The fastest tunnel will be the one that doesn't run on the water.  It won't be a boat at all.  It will be an simple airplane that only flys on the water surface that looks like a tunnel hull.  Figure out how to do that and your there.  My engineer colloge teacher always told me "Don't over think it!!!!"

Josh

Precision Boats

P.S.

"Wake Up America!!"

Ole Man Says - "Run a Lynx or chase a Lynx? - Such a simple question!"

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The list of names of the boaters that consistantly win boat races changes very little but the list of the manufacturers of the boats they run do.

Put a decent boat in a great boaters hands and you will have a consistant winner.

Now I am not saying that the Lynx isn't a good boat but there are a lot of good boats out there.

A fast tunnel boat is an aired out tunnel boat.Everybody understands that."When in doubt,air it out"

The Lynx is just the latest tunnel boat to appear towards the top of the Hit Parade list of good boats.That is a direct function of the people that are running them not just the boat.

I started this thread to generate interest in tunnel design and encourage some of you to start building boats and learn something about tunnel boats other than just how to spend $$$$.That is what the For Sale forum is for.

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This has been an interesting topic....And I think its well known that designing tunnel hulls is one of the trickiest objectives in the model boating world. From a designers point...A nightmare. I know at one point in my exploits way back when, we thought air only played a big part in tunnel design, (which it does). Then after building upside down tunnels between the sponsons, different airfoil sections with rises at the rear, no rises at the front, flat bottom airfoils, etc, we saw some other effects that the waterspray inside the tunnel had on the boat. Now, not only is there air (speed, volume), but now water acting on the inside surfaces of the tunnel. Again, speed and volume of water. As you change the airflow through the tunnel, you also change the amount of waterspray that flows around and through the tunnel and acts on the surfaces. Theres the nightmare. Think of the sprayrails as well that are added to the running surfaces or sides of sponsons and the effects of such devices.

From a drivers point....I've always said.....Learn to drive a tunnel...and you will drive any mono or hydro better than the one who starts with a hydro or mono. There is just so much more happening with a tunnel than any other type of boat. Thats my 2 cents so far.....

 

[[email protected]]

This is too funny...... :lol: :lol:

 

[Lake S.P.O.R.T.]

I understand the atmospheric pressure thing. It is what makes any carburetor work. The venturi in the throat creates a low pressure area by accelerating the airstream. The fuel is not sucked up the nozzle. It is moved up by the difference in pressure between the venturi and the atmospheric pressure that is ALWAYS present and constant on the fuel in the float bowl. Atmospheric pressure is easy to forget about...just like gravity...invisible...out of sight out of mind. I think that is what Rod is trying to remind you about.

I am also convinced that tunnel boats can be PULLED OVER backwards just as much as BLOWN OVER backwards. And I don't mean pulled simply because of too much lift in the deck. Anyone else here ever see the famous and stunning series of pics where 3 tunnel boats (one of which was Reggie Fountain) all "blew" over together at Miami Marine Stadium? Why I am I convinced? I have seen it many times. It is not always a gust of wind or the boat packing too much air that STARTS a blow over. This is where a wind tunnel and a smoke stream would be very useful.

 

[Geraghty]

I understand the atmospheric pressure thing. It is what makes any carburetor work. The venturi in the throat creates a low pressure area by accelerating the airstream. The fuel is not sucked up the nozzle. It is moved up by the difference in pressure between the venturi and the atmospheric pressure that is ALWAYS present and constant on the fuel in the float bowl. Atmospheric pressure is easy to forget about...just like gravity...invisible...out of sight out of mind. I think that is what Rod is trying to remind you about.

Absolutely right!The faster the air is being exhausted out from under the tunnel the lower the pressure is under the boat at the tunnel and atmospheric pressure pushes the rear of the boat down in the water raising the nose even farther.

 

[Geraghty]

Hi Tommy,Great to see ya here posting again, Please chime in on any of my posts,  Or any tunnel post for that matter, I like to hear you opnions on stuff   

Ok Rod, a "BIG" lite bulb just went on with me, Dont know if anyone got it but, Did you say that the cowl sides comming down at a angle to the top of the decking (large fillet where the cowl meets the deck) will keep the boat from blowing off, Did I read that one right ? like Tommys XTR21

Pic from Paul@Xtreme,

Gene 

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Absolutely right.A squared off cowl and deck is nothing but a turbulent flow mess.

With that fillet you have now turned that deck into a control surface.You also need to have rounded sponson edges and the front of the center section rounded to really complete the task.

How many times have you ever seen an XTR.21 just lift off and blow flat over backwards?