Tunnel Hull Design

[Bill Britton]

Good idea pinning this. Great info in here!

 

[Slideblues]

Hey Bill,

Glad ya showed up,Had a few questions bout the Sniper II sponsons.

First when Rodney showed me tha pics I noticed how different yours are.

Care to talk a little bout how you came about that design?

Gene

 

[kesso2118]

Hey Rodney, thanks for your response about the effects of steering pin angle, however, here is an extract from an older thread, which I think might be the opposite of your findings,

"............What you saying by moving the hinge pin angle does have an effect. Lets go to an extreem for sake of argument and move the pin 30 degrees off of vertical. The top being closer and bottom extended will make the lower lay over as it pivots and lift the rear and drive the nose down. Go the other way top out and bottom of the pin in twords the transom will cause the skeg to dig in at the rear and lift the nose. This is assuming the skeg (rudder) and the lower remain vertical. This is an exagerated example of course. I never could figure out rake and trail angles on motorcycles either............."

I'm so confused :wacko: :wacko:

 

[RodneyPierce]

Kesso, give it a shot. Only way to find out for yourself. After all, its not hard to add a piece of .063 shim stock behind the top 2 bolts... I have read what you posted above more then once, as there was a great discussion on this a while back. Ill have to look at my boat again here this weekend and Ill try both directions. I encourage you to do the same...

 

[kesso2118]

Yep, I agree Rodney, that's the only way I'm gunna be able to convince myself.

At the moment, I'm experimenting with different props, so I'll try it once I think I've got the prop with the best speed & handling combination..................... this could take a while :unsure:

 

[LarryConrad]

I Shimmed the bottom of the mount to give the hinge pin a top forward angle on one of my XTR-21 Leecrafts, that I had an OS lower on. It help a bit with the some of the cornering issues I had with that boat. Jerry Wyss turned me on to this trick back when I was running the XTR-21.

 

[RodneyPierce]

Kesso, I will try it this weekend with mine again also. Both directions and report back to you.

 

[Bill Britton]

Hey Bill,

Glad ya showed up,Had a few questions bout the Sniper II sponsons.

First when Rodney showed me tha pics I noticed how different yours are.

Care to talk a little bout how you came about that design?

Gene

By going to the pond every weekend for about a year and a half (but not racing) and A LOT of boat building.

 

[Mark Poole ModVP]

Model tunnels need stumble blocks for a very basic reason. Imagine throwing a full size tunnel into a corner at 250 mph with no power trim.

 

[Geraghty]

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,

Carl,

I thank you for the nice words......

As you well know in the last 30 years Tommy Lee and I had been all over stumble blocks from every angle imaginable.........

Boats with blocks were "always" faster around the race course than boats without....That told us something......

We proceeded to find out why this was true.......

Tommy and I also noticed that boats without blocks tended to do something stupid [spin out] when you least expected it.....

99% of the tunnel records in IMPBA and NAMBA are all held with boats with blocks......that should also tell us something.....

Once again thanks........

But...the best part of your kind words is it gives me the perfect opportunity to get off this keyboard merry go round on this subject......

Have you noticed that it is very seldom that model boating national champions or record holders and icons seldom if ever contribute to a subect such as tunnel boat design.....

Virtually every technical subject raised on keyboard forums eventually digresses into a pissen match.......there is always somebody that tells you that you are wrong but they "never"show you how you are wrong with scientific evidence or good emperical testing and they never tell you how to do it better......

It is always he said or she said ....or I read ......but never "I know because I have tested this and ,,,,yada yayda yada "...............

There is a ton of model boating experience out there that will never contribute to this or any other forum because they know they will eventually end up trying to defend a post they know to be true because they personally have been there and done that.....What people fail to realize is all these champions,builders and record holding

experience has spent many years doing it wrong and that is how they learned to separate the flies from the manure......They are not any smarter than anyone else just more persistent in search of success.....

There is no magic bullet to tunnel boat design........there are no speed secrets.....there is only experience and how to apply.it....................

I extended an invitation to talk to anybody,anytime,one on one about tunnel boat design.....That invitation still stands...

I will be more than happy to share anything I know to be true because I have been there with either good science or good emperical testing.....

Rod Geraghty

 

[RodneyPierce]

Rod, thanks for your contribution. I will call you here sometime. But I dont understand why everytime people think it has to turn into a pissing match over something. Thats not the point of this or many other threads, period. Just because someone has seen or read or whatever on a subject, doesnt mean they are disagreeing or trying to make you or anyone else defend anything. I dont want people to think that way please. We all learn from each other! Well, I know I do atleast! As you have said, stumble blocks DO work, and I dont think anyone here is arguing against that point. If you or anyone else took it that way, I dont think it was meant to be taken that way. So, if you want to continue, awesome! If not, well then, thanks very much for your guys contributions!

 

[user 115]

Anyone that is even remotely hesitant to call and talk to Rod, don't be. He'll end up talking your ear off!!! Rod, you are a fantastic ASSet to model boat racing.. I'm still mad at you for never letting me buy that orange tunnel!!

 

[Geraghty]

Rodney,

What I had to say had nothing to do with sour grapes.....I don't need a shrink or a priest....... Frankly I really don't give a xxxx if another model tunnel boat is ever designed.....

All I was trying to do was to generate enough interest for future boat designers to research what is happening on the bottom of a sponson in contact with the water....

What is actually happening on the bottom of that sponson is the exact opposite of the popular he said,she said thinking so prevalent in model boating today.....

Bernoulli and Coanda are not up for personal evaluation ....they are facts of science.......

I have been on IW 8-1/2 years and RCboat.com many years before that.......This is not my first rodeo.....

I have read a ton of technical threads and seen where they go and why the most experienced boaters do not contribute........All I was doing was but stating a fact of observation.......

 

[RodneyPierce]

Fair enough Rod. And I agree, they have been around forever and are indeed facts of science. And LOL @ the shrink or priest comment. haha, I never thought you did need one. Its cool discussions like these that get the wheels turning of people like myself, and others in the hobby that want to design there own tunnels, or improve apon what they might already have. Thus why I try and start some of these more technical discussions if you will. I will give you a call sometime here in the near future and chat about for a while.

 

[Slideblues]

During anyones testing what did you find to be the hardest to achieve ?

Turning in without spinning out or stuffing, Or speed without blowing off.........

Gene

 

[Bill Britton]

Not to try and hold anything back from the conversation, or have anyone think I am a tunnel design guru. I am not by any means. I don't build the Sniper any longer and have not built one in at least 1 1/2 - 2 years. The original version was ok for stock use in my opinion but not much more. The second version (wood) handled VERY well. It would turn like it was on rails, but would not hook unless the CG was way off.

It did not have any stumble pads as I worked and reworked the design until they were no longer needed. Ask those who have driven a wood Sniper and I think you will find that they will tell you that they have never seen a tunnel boat carve a turn as it did. It did not lose speed in the corners as some would suggest a tunnel boat do without them, and was fairly forgiving about blowing over if you payed attention. I don't credit the success of the wood version to any special skill I posses, I would rather think that I just happened to hit on something that worked well.

That being said, I am a devout Lynx/Shaman/Warhead fan. Carl is a master at designing tunnels and as far as I am concerned I will run his boats for as long as I am in this hobby. The Lynx in my opinion is the best 20 tunnel hull ever made, period.

There is no substitute.

 

[LarryConrad]

During anyones testing what did you find to be the hardest to achieve ?

Turning in without spinning out or stuffing, Or speed without blowing off.........

Gene

Gene, When I was running a TS2 keeping it from blowing off was a major problem for me,my second B tunnel race boat...after destroying my TS2 in a blow over was a XTR-21 Leecraft.Mine were very fast down the straights with very little tendency to want to blow off, but were very difficult to maintain the speeds through the turns with.At first I would barrel roll them. After cutting out the top of the shelf so I could place the fuel tank in the bottom of the boat to lower the center of gravity the boat would spin out instead of flipping over.I lead a lot of heats with my Mac powered XTR-21 that I didn't finish. In 2009 Rod sold me a Nemesis kit he had. I have only raced that boat a handful of times, as my career change in 2010 has pretty much sidelined my racing efforts. My limited experience with the Nemesis so far has shown that the boat is very stable with little tendency to blow off in the straights, and will maintain good corner speed. When Ron Drake uncovered the long lost stash of unobtainium in 2009, I was finally able to get a hold of the boat I wanted to start my tunnel career with, but I have not had a chance yet to put my Lynx in the water.

Larry

 

[Bill Britton]

When Ron Drake uncovered the long lost stash of unobtainium in 2009, I was finally able to get a hold of the boat I wanted to start my tunnel career with, but I have not had a chance yet to put my Lynx in the water.

Larry

Larry,

Once you drive it you will want nothing else. There is no other boat with the same performance and stability. The Lynx is in a league by itself.

/B

 

[Tim_Duggan]

Yep, I agree Rodney, that's the only way I'm gunna be able to convince myself.

At the moment, I'm experimenting with different props, so I'll try it once I think I've got the prop with the best speed & handling combination..................... this could take a while :unsure:

James,

I've used and tested pin angle on every O/B tunnel I've ever built with an OS or TT lower. Some benefit, some don't. From what I've seen of your tunnel - I think it would benefit.

Things that work for me.

1. Pick a prop and CG % and stick with it when experimenting specifically on pin angle.

2. If you go changing or tweaking the prop whist trying to determine the effect of changing the pin angle, it introduces another variable. Lift characteristics alter the effect.

3. Reset the angle behind the pin after making a change to pin angle or the boat will run too light or too wet in the straights depending on which way you are going with the shims.

My current sport tunnel runs a shim between the transom and the bottom engine mount screws. I have tested i with and without, & it keeps the nose from digging in too hard on our 5 buoy turns. Certain prop characteristics exagerate the phenomenon more than others. When I switched props a while back, I had to go thru pin angle again as the new prop had to run with more negative in the straights to prevent it being too loose. More negative behind the pin usually needs more shimming to keep the nose up in the turn.

 

[LarryConrad]

Bill,

I haven't even drove it yet and I want a Warhead! The Lynx will be nitro, The Warhead I'll set up as a P FE.