Tunnel Hull Design

[Geraghty]

http://www.youtube.com/watch?v=olVJzVadiFs

This is happening with the water were it touches the sponsons as well as the air moving across the boat......

It took many many trips to the pond to discover that control of the water off the sponson bottoms and sides is the major key to a boats overall performance.

After you understand Bernoulli,Coanda and Venturi you will discover there is no such thing as a "speed secret" to a boats bottom.....There is only knowledge of basic physics

and hydrodynamics and how it all applies to model boats.....

I discovered the "stumble block" in 1980 and that was the day the light went on for me......Prior to that I had scratch built over 30 tunnels trying to stop a tunnel from spinning out before discovering the stumble block.

It took me 30 boats to realize that if every tunnel that I had scratch built would have had a set of stumble blocks attached to the tunnel floor it would have been an A+ performer.........

That was the day I realized that the tunnel boat experts had no clue what was happening on the bottom of the boat.Boats were being built to look good ,not run good.....

 

[Baxter Walton]

Rod that was on the money! I have just been sitting back reading, I found that no one talked about the can't angle, or a non trip chine. Only dead rise. While I am not a hull builder nor do not want to be. I do read enough to understand design.

 

[RodneyPierce]

alright guys, call me ignorant, but im having a heck of a time trying to relate that to boats, in any way that makes sense to me. Perhaps you can try and enlighten me?

 

[Grimracer]

cant angle is such a dangerous design element. I have found it best overall to just set em 0.

Having said that pos cant angle is best avolded.

Grim

 

[Baxter Walton]

The Leecraft has 2deg If I'm correct, Rod? Am I correct?

 

[Geraghty]

The Leecraft has 2deg If I'm correct, Rod? Am I correct?

I don't remember exactly what cant a LeeCraft has but a glass boat has to have positive cant [better known as draft] to get the boat out of the mold.

The degree of cant,positive or negative,can be compensated for by deadrise angle and sponson bottom width.......you have to sink the sponson to turn the boat.

 

[Geraghty]

Rod that was on the money! I have just been sitting back reading, I found that no one talked about the can't angle, or a non trip chine. Only dead rise. While I am not a hull builder nor do not want to be. I do read enough to understand design.

If the the tunnel sponson is designed properly ,you don't need a non-trip......remember,the inside of the sponson is the tunnels turnfin.......the sponson has to be designed to sink in the corner.....

 

[Grimracer]

I try to stick to my general rules of design. Grim designs and builds great boats and always brings some clean and fast boats to every race.

I would call him a "model sportsman". One year in South Carolina, I saw him give up lane one (on lap six) to keep from making an infraction that would have knocked someone out of the race and indoing so, lost his own chance to win first place. That is a true sportsman right there! He is awlways fast.

I don't make it out much anymore but I always enjoyed seeing racers like Mike.

-Carl,

Thank you Sheriff!

Grim

 

[jeepers]

This is a great thread, keep it going guys!!

 

[David Moyle]

If the the tunnel sponson is designed properly ,you don't need a non-trip......remember,the inside of the sponson is the tunnels turnfin.......the sponson has to be designed to sink in the corner.....

Rod - what have you found to be the mechanism that causes the sponson to sink in the corner? Loss of aerodynamic lift due to speed reduction in the turn, or something different? From experience I've found that if a hull is truly "flying" efficiently down the straight, it's reluctant to change direction without a reduction in speed because there is not enough hull in the water to 'bite' at full speed.

 

[David Moyle]

That's a good point Greg, that certainly does help bring the nose down. From what I've seen it's more of a fine tuning tool though.

 

[kesso2118]

Thanks for starting this thread Rodney, there is some good information coming through

Can someone, who has actually made changes to the steering pin angle, please explain what they achieved i.e, which way was the pin tilted and what was the effect.

The other point I would like to understand is why stumble blocks are used, what is the problem they are meant to fix? Is it to prevent boats hooking in the turns or something else?????

Please keep the good info coming..... B)

Thanks,

James

 

[RodneyPierce]

James, I have been experimenting with the pin inclination myself on my current tunnel. I run the tunnel very aired out like David describes above, and with such little sponson in the water, there isnt much there to hook the water, and sink the sponson in the corner. So, I have been messing around with the hinge pin. I currently have the top of my pin tipped back. Pointing away from the transom about a 1/16 of an inch. It really did make a difference. This seems to have forced the nose of the boat down when I turn the motor. Really helps the boat start to turn in. Then, once the nose falls, it rails the corner.

As far as stumble blocks, I believe they are designed to keep the boat from digging into the infield when your making the corner. Helps the spinning out, and hooking. Someone, please correct me if im wrong there.

 

[Geraghty]

If the the tunnel sponson is designed properly ,you don't need a non-trip......remember,the inside of the sponson is the tunnels turnfin.......the sponson has to be designed to sink in the corner.....

Rod - what have you found to be the mechanism that causes the sponson to sink in the corner? Loss of aerodynamic lift due to speed reduction in the turn, or something different? From experience I've found that if a hull is truly "flying" efficiently down the straight, it's reluctant to change direction without a reduction in speed because there is not enough hull in the water to 'bite' at full speed.

Loss of aerodynamic drag has absolutely nothing to do with it.....

Bernoulli and Coanda causes the sink......the more the rocker in the sponson length and the steeper the dihedral in the sponson bottom the more and faster the sponson sinks with directional change....

Hold a big spoon loosely by its handle and back that spoon into a fast running stream of water and see what it does.......The spoon is sucked [with great force] into the running stream of water.......That is what a sponson does on a running boat.....

Guys,I have neither the ,stamina nor the typing skills to moderate a seminar on Bernoulli and Coanda on this forum....there are literally dozens of demontrations on you tube of the Bernoulli and Coanda principles....

Look at them and wrap your mind around how they would affect a sponson ....

Hint: I.E....When you suck on a straw you are not sucking anything up that straw....you are creating a vacuum in that straw and atmospheric pressure is pushing the fluid up the straw......That is what is happening on any curved tunnel sponson,hydro sponson mono bottom etc,etc etc.....

I would be glad to discuss this in depth in a one on one phone conversation .....1-715-926-6096

Note:The entire JAE boat has incorporated flat plane technology [that being no bernoulli effect] on all of its hydrodynamic surfaces.....that is why it works so well where absolutely no mechanical adjustments to the JAE designs are needed.......

 

[Marty Slater]

stumble blocks

bandaid

wise man once said cures for a ill handling tunnel boat

 

[Kris Flynn]

Hey Marty,

I think that was Jim at Aeromarine Research that said that? I agree with Carl, our boats are completely (well mostly) different in actual specs (ie deadrise, AOA ......) than the fullsize boats.

I also think the blocks help as a sort of air 'dam' to help keep the boat on the water by creating low pressure behind them.

On most boats I have driven they give no warning they are going to blow off, but I know the Vision (maybe the Lynx, can't say I have been watching one properly when it blew off) slowly rises the bow, then bang over she goes. I think the blocks (position and shape) have a part in this.

Kris

 

[RodneyPierce]

Kris, I have a Sniper II that has no stumble blocks, and it gives GREAT warning before it blows off the water. Its actually the best tunnel i have had in that respect. Since I have learned to watch for it, the boat gives enough warning, just like you describe. Bow slowly starts rising and dancing about. Giving you enough time to let off and let the boat settle back down, and continue on, assuming your paying attention.

And I think Marty is referring to Mr. Jim Irwin, who told us the theory of stumble blocks as a band aid for fixing an ill handling boat. (not that I agree or disagree with this theory, as they have been proven over and over to work, and work **** good)

 

[Carl Van Houten]

I have found that if you leave the "Rod Blocks" off (That's what I like to call them to make sure that he "Rod" is always credited to have stuumbled onto them) Just kidding Rod! I love them!

But all of my boats have them and here is why: It is a variable compromise that takes out a lot of negative and inherit problems you will incounter out when you design or "try to design" something that wants to dart infield at the slightest turn of the wheel. Two things a O/B tunnel loves to do is TURN and BLOW OFF!

As you know, I have designed all my boats using Rod Blocks. I design mine to be progressive with the intent of only using what I need. Why slap it all down at one time and pickup all that drag if you don't need to???? Remember "Drag is the devil".

Now, I will go ahead and tell you guys who are thinking about designing a tunnel, and this is a fact, you can not fix a ill turning boat with Rod Blocks alone UNLESS it is already close to turning good to start with. I design mine to "feather" my turns ONLY. They can't do but so much because of the ratio of surface area combined with their angle of attack weighed against the length of the sponson. The sponson will win that battle if it is far off.

Can you build a boat that will go thru the turns without Rod Blocks? Yes. But there must be a reason why there is not one O/B tunnel that turns good without Rod Blocks after all these years. If it was that easy, someone would already have one. If there is, I havn't seen it.

I like to choose my battles when I have a choice. In this case, don't fight it, use them and use your forehead for head butting the really big problems you will be faced with like how to keep a really fast tunnel on the water for six laps or how to design a boat that will not require 10 to 16 ounces of lead to finish a race and not stuff at the end of the straits, tail walk, barrel roll, hook or flat spin in the turns. These are your first big issues.

I want to see people get onfire for tunnel design. It is not a "plug & go" task. I average one fair design about every 5 to 6 years and I have done nothing but O/B tunnel design for 30+ years. I guess what I want to say to you guys is find a test pond and test your boat until you dry all the water up!

I am signing off this thread because I don't want to step on any toes here. I am finishing up my last model now. It was fun. I learned a lot. Drake will build my boats until he gets too old like me to build them. I hope I said something that helps.

-Carl,

 

[RodneyPierce]

Carl, thanks for your input to this thread! This is getting good, lets keep it going. I know there are many who are reading it, and im sure taking some great info from it. I do wish you would keep active here with any answers you care to give! Its much appreciated!! And no worries of stepping on toes. We all live and learn from others. Some may like it, some may not.

 

[topfuel443]

Pinning this for a while. Some VERY good info, listen up!