3.5 Tunnel SAW record

[Russell Bear]

Or a polygraph

 

[Propjockey]

Y'all quit pickin' on Jim... B)

 

[Grimracer]

LMFAO

grim

 

[Tunnel Hull]

Come on Jim, near 80MPH??? 85 plus this Summer????? Thats 5 to 10MPH over Tommys record that took a few years to reach!! Lets see the boat run at an IMPBA time trials to run this speed and shut me up!! How about setting a verified record before you blow!

 

[Bob Kensill]

I agree with Rod,get a boat running good and drive the h**l out of it till you know every quirk of it. I have been running the same 21 tunnel since 1996 and the same 45 tunnel sunce 1991. My boats are far from being the fastest boats at the race,but I can drive them!. As far as SAW tunnels go,I don't think there is any magic formula for the right length or weight. I think it will take just the right prop and a good setup that will let the motor buzz that prop. As Rod also implied,you are going to break alot of parts before you get there.

Bob Kensill

 

[Slideblues]

You can plug in some numbers and get a target range that you can shoot for, But the length thing is still a mystery to me, seems like the longer the hull or increase of wetted surface, the more drag ya get, to me anyhow :blink:

 

[Geraghty]

More ramblings...............

11.Gases are compressible,liguids are not.

12.Everything under the water is drag.

13.Aerodynamic "drag" [or loss of speed due to drag] under lets say 80 mph is virtually negligible.Aerodynamic "control "affected by the design or shape of a boat,now that is huge.

Now on to the mother nature stuff[basic physics]........... :blink:

The "Bernoulli principle".This Bernoulli guy was a Swiss physicist born in the 1700's.He proved that as velocity increases,pressure decreases and vice versa the converse is also true.

If you understand this one principle and learn how it applies to model boats and 2-cycle motors,you will be head and shoulders ahead of 98% of all people involved in model boating today.That includes boat designers,boat manufacturers,motor modifiers,etc,etc,etc.

Chew on this for a bit.......When you suck on a straw,in fact you are not sucking anything up that straw.When you suck on the straw you are creating a vacuum in the straw and "atmospheric pressure" is exerting pressure on the top of the liquid in the glass and is pushing the liquid up the straw.Remember this example of basic physics....

Here is a easy experiment for you to try.

Take a serving spoon[the bigger the spoon the stronger the effect] and attach a piece of tape on the handle as shown.The purpose here is when you hold the suspended spoon by the tape,the spoon will swing like a clock pendulum.

Take the spoon to the sink and turn on the water full blast and holding the hanging spoon by the tape, just barely touch the "back" of the spoon to the water stream as shown.

If you do this right ,the spoon will suck into the water stream and it will take a fair amount of force to remove it."You have just experienced the "Bernoulli principle"!

Atmospheric pressure is "pushing" the spoon into the water stream."The force of old mother natures atmospheric pressure is amazin,ain't it!".

This is what happens with sponson bottoms that have a nice gradual swoop from front to the rear.The wider the sponson and the bigger the swoop the more the force.

99 times out of 100 this is what is happening when you have a boat that does real stupid things and when you get the boat on dead flat water this phenomena just gets a ton worse.

This is what is happening..........

Lets say a boat is going 50 mph.The water is then entering the front of the sponson at 50 mph.That means the water is going to come off the back of the sponson at 50 mph since the boat is only going 50 mph,right?.

Here is the rub.Since the water travel on the sponson is not traveling in a straight line the water has to travel a longer distance to exit off the back at the 50 mph because the bottom of the sponson is rounded.In order to do this ,the water has to speed up to 55 mph in the middle of the sponson in order to maintain the 50 mph exit speed off the back of the sponson.The pressure on the sponson is reduced in the 55 mph area and creates a vacuum at that 55 mph area and "atmospheric pressure" pushes the sponson down with great force onto the water.This is why tunnels,monos and all types of hydros violently spin out or nose steer.

This is also what is occuring when you can't get a hydro to launch.Not only are you experiencing the Bernoulli principle on the front and rear sponsons but you are also experiencing it on the tub.

To end the experiment turn the spoon around so the rounded part of the spoon is not in the water stream and try again to gently insert the spoon into the stream.There is no way that spoon will stay in that stream.........remember this.

If this is confusing just tell me what area baffles you and I will try to explain it a different way.Just keep asking until the light comes on you understand this principle.

The Bernoulli principle is the same in air or water.The effect is the same.Remember this also.........Later I am going to go right in the face of conventional wisdom with facts that will really stir the sxxt.Apply the Bernoulli principle to hydro turn fins and tell me your conclusions.

My finger is sore again. More later......

 

[Geraghty]

Photo #2 & #3

 

[Geraghty]

Opps,wrong order.

 

[Kris Flynn]

Thank you Rod for sharing your Knowledge! it is very interesting so far!

My Fingers would be sore after typing as much as you are, so it makes me appreciate what you are doing even further that i know you would rather run your fingers into a belt sander than type

Kris

 

[Slideblues]

Ok, so the rocker designed in most of the boats out there has the adverse affect that you just described, But if your hull has no rocker, and the ride surface is flat foward 11" from the sponson backs, then you would add strakes to break up the suction you just described correct?

Gene

 

[Bob Kensill]

I think that you don't understand what Rod is saying. The rocker helps your tunnel settle down for the turns. The straight are needs to be that part that can touch during straight away runs. If your sponsons had longer flat areas it would change handling drastically. Creating bubbles along the running surface will help break up the suction.

 

[izitbrokeyet?]

The Bernoulli principal can be applied to many parts of this hobby and is a spin-off of the Law of Conservation of Energy

The mathematics of the Bernoulli Principal is as follows:

ET + EK + EG = k

for systems that do not involve gravity change, this becomes

ET + EK = k

Thermal energy + kinetic energy is everywhere constant.

Now since ET = PV and EK = Mv²/2

PV + Mv²/2 = k

Restated:

The product of Pressure and Volume plus 1/2 the product of Mass and the square of velocity is everywhere constant.

Dividing both sides by volume,

P + dv2/2 = k

and, rearranging,

P = k - dv2/2

So, an increase in velocity indicates a decrease in pressure.

 

[Slideblues]

:blink: The hull I just described was my Villain, as far as rocker goes, mine dont need it

 

[Mark Walter]

Awesome info Rod, i would think that steps added to the sponson bottoms would help reduce suction and drag. MARK

 

[Grimracer]

Racers

PSRP does not use rocker in any of our designs. That is to say that the sponson riding pads have no rocker.

The Villain S1 sponsons rocker up but only after a measured amount of flat length. Is this rocker...sure But not on the aft area of the sponsons.

Is all that Rod said true...Yep to me it is...he also said in any early post that everything is a trade off..

Just could be that rocker is only relative to the boat design... and what you want the boat to do...

Blistering straightaway speeds...trade off

Great cornering.... Trade off

Rough water…. trade off

Smooth water...trade off

The boat design that matches the drivers abilities and expectations is a good boat.

The same boat that does not is a bad boat....

As far as boat design… I think Andy Brown said this best...Gentlemen.... chose your weapon...

Even though it looks like I went off course on this post…I did not.. Rocker / surface tension is the single largest boating design obstacle to overcome; this is in regards to speed and handling.

Everybody….go make a run with our tunnel. lay down your best pass… Then use a little car wax on the bottoms and do it again…what happens….you tell me..

As Chevy Chase once said… BE THE BALL….some might get this and others will not…thats OK

ROCK ON…

Grim

 

[Slideblues]

Anybody Hungry ? :lol:

I'm a goin ta lunch..........Rod!!!! Pic'e Post'e, Pic'e Post'e

Gene

 

[Preston_Hall]

So, for straight line speed and handling the "tunnel ceiling" or bottom of the boat should be parallel to the water when at speed? Thus removing any pressure differences from front to back. Like a shovel nose boat. Of course the top should be parallel as well I suppose.

Another thought. When a cowl is added to rigger, you have just increased the velocity of air across that section. So there should be more lift due to less pressure. But you will here that adding a cowl provides more down force or at least makes the boat tighter to the water. Personally I have seen this addition make some boats lighter.

Turn fin principal..............well a feathered race-course-side edge makes a lower pressure to that side and therefore pulling the boat to the inside. True. But I took the stock SGX fin off, put on a feathered edge, increased left trim and went 2 mph faster with no other changes. So the drag of the blunt edged fin was more than that of the left trimmed rudder.

The last 2 paragraphs were just rambling. Keep it to the first.

 

[Grimracer]

So, for straight line speed and handling the "tunnel ceiling" or bottom of the boat should be parallel to the water when at speed? Thus removing any pressure differences from front to back. Like a shovel nose boat. Of course the top should be parallel as well I suppose.
Another thought. When a cowl is added to rigger, you have just increased the velocity of air across that section. So there should be more lift due to less pressure. But you will here that adding a cowl provides more down force or at least makes the boat tighter to the water. Personally I have seen this addition make some boats lighter.

Turn fin principal..............well a feathered race-course-side edge makes a lower pressure to that side and therefore pulling the boat to the inside. True. But I took the stock SGX fin off, put on a feathered edge, increased left trim and went 2 mph faster with no other changes. So the drag of the blunt edged fin was more than that of the left trimmed rudder.

The last 2 paragraphs were just rambling. Keep it to the first.

Preston…how you doing…good I hope..

I also saw TopFuel on here somewhere…ROCK ON TOP FUEL…

True in idea format but not in practice.. Having the tunnel parallel to the water is just not possible. The boat will find a attitude “home” and you had better force it positive because you do not want negative… its air time for the boat when it finally does come off the water. (and it will come off the water).. Should the tunnel top be flat…no way…bad goings on will again happen. its all about the trade offs.

Negative is a negative… For sure..

There is more to it then this.. the passing of air through the tunnel and the speed that this happens at… The AOA of the tunnel, and the relationship this has to its quickness out of the corners or to top break neck speed.

Man this stuff goes on and on… for instance your hydro cowl observation… this is why I like stumble block on my tunnels…same reason. Some guys don’t buy it, but until you have been bitten a few times the performance gains large or small are still gains.

I like stumble blocks..There just not for breakfast (cornering) any more….

Love the fathers of tunnels or not. if its faster that we want we better DW listen..

I for one cant get enough…

ROCK ON

grim

 

[Geraghty]

Remember I said everything is a compromise in boat design.

Rocker does cause the condition I described but it isn't necessarily an "adverse" condition if designed in properly.

Look,loose tunnel boats run very fast.The challenge is to get them to run them loose and fast under control.

Remember the tunnekl boat creed....When in doubt,air it out!!!

As a general rule and all things being equal such as sponson depth,width,dihedral,boat length etc,etc,the longer the flat you have in the sponson bottom the harder it is to get a tunnel boat to run loose without having to trim in a very nose high attitude.

Strakes as I know them running front to rear of the sponson don't stop the Bernoulli principle or its effects.Now steps across the sponson and the judicious use of spray rails will greatly reduce the Bernoulli effect on the boats riding surfaces.

Note;The bernoulli effect also occurs on the chine[sponson side]as well as the sponson bottom.

I'm not saying any one boat design is better than another and I don't want this discussion to even begin to go there.

I am sure Mike Z. will confirm this but I had a ton of input into the Villian.Ratio wise the Villian has close to the same amount of rocker as a LeeCraft and I suspect a Dunlap WOF.

I know Mike Z.'s motors are not all cut to hell.They don't need to be.The boat is letting the motor run hard and fast.

All I am trying to do is tell you why things happen and what causes them.

I will also tell you if something will not work or be counter-productive..

Here is a little more tunnel boat history...........

I told you I started building tunnels in the late 70's. The most popular boat in the west at that time was a boat built from model builder plans.It was called the Excalibur.It had 6 degree sponsons and ran a turn fin.Not a bad little boat put you had better not try to turn left.Also all we had was J.G. props."X" series Octuras didn't come along until the early to mid '80's.It was not unusal to have 15,maybe more 3.5 OPC tunnel boats show up at a race.

My goal was to get a tunnel boat to run fast and turn without a turn fin.The only way this could be accomplished was by increasing the sponson dihedral and putting rocker on the sponsons and use the sponson as a turn fin.Increasing the dihedral & installing rocker allows the sponson to sink and become a turn fin.Rocker meant speed and ease of set-up and trim and dihedral meant no turn-fin.

The increased dihedral and rocker made the boat very easy to trim and set-up and the boat got real fast.The boats were just amazing up until the time you tried to turn them.Thats when all hell broke loose.

As I increased the sponson dihedral and rocker the boat became very spin out prone.I could tippy toe through the turn but at a greatly reduced speed.The faster I would attempt to turn the more often I ended up in the chase boat.

I knew the boat ,in a turn, was rocking up on its nose and allowing the skeg of the motor to un-hook and since the skeg was the directional control surface[rudder]around the boat would go.This was the original K&B skeg that was about only 3/4" deep.

I fought this problem for the better part of a year and a half and you can't even imagine all the "speed secrets" that were offered as the solution to this problem.The "speed secrets" ranged anywhere from the tangent of the earths axis to the finish prep on the bottom of the sponson.I bit and gave precious time to all of the "speed secrets" :blink: trying to solve the problem.Frustration is the mother of all brain farts.

Then one day at the 1980 NAMBA nats in Tacoma Washington during open water,I was still fighting the spin out problem,when Ed Fisher was walking by and said don't you wish the rules would let you put a ski on the front of that boat so you don't have to keep rowing for it."The light went on.........Duh,I was going to have to hold the nose of the boat up mechanically".

That was the day yours truly came up with the "stumble block" .

I went over to the side of the pits and cut a piece of peckerwood off a small sapling and whittled with my jack knife the first stumble block.I installed one only block on the right side with 5 minute epoxy and 15 minutes later I was back on the course.

It was absolutely awesome.That S.O.B. went around a corner like it was tied to a post and the faster you went the better it turned.Now I still couldn't turn left but that just meant I neede one more block on the other side.That was 24 years ago.

After giving 20 minutes to analyzing the solution , the spin out cause was evident.Bernoulli,Bernoulli,Bernoulli!

[That day taught me a lot.There are no speed secrets there is only "legitimate" science and application.I chased my own a$$ for over a year listening to "speed secrets".I was exactly what ignorant looked like.Dam I was dumb and I knew better.]

From 1980 to 1983 I built literally dozens of tunnel boats and had several people driving my boats and giving me feedback.The boats just got better and better.

The first sanctioned race I personally entered and drove in was the 1983 NAMBA Nats in Burnaby B.C.

I was fortunate enough to win the 1983 NATS in 3.5 OPC,but you know,it is easy to race and win when you have 5-10 MPH on the field. I just stayed out of trouble and lapped about 95% of the boats I raced against.

Bobby Tom of K&B was at that race and he told Tommy Lee about the boat and about a month later Tommy and I got hooked up.A year and a half later the LeeCraft XT460 was born and the rest is history.

The model boating world has no conception the amount of building and test time that was put in by Tommy Lee.His success was no accident.

If I built 40/50 boats doing R&D Tommy has built at least 2 times that many.Tommy just liked to build boats.His wood work is absolutely magnificent.

[Over the years I know I must have put at least 25 boats in the burn barrel and I will bet Tommy has burned at least that many .]

Tommy and I are very close and I know there are boats he has never mentioned and I have never seen. Every once in a while he would surprize me and one would just show up at a race or a record trial.

I see there are more posts that are not covered here......Good I'll address them later