Experiment #1

[Jerry Wyss]

Wow, Ya Really got me goin' now, along with about 36 other people :lol:

I remembered something I did back when I was Modding the DPI 1/4 scale

tunnel (plastic boat) I developed a way to get them to turn the way We need them to turn for our type of course (track). I had to put "rocker" in the sponsons,They turned MUCH better,but I also did something else in an effort to "cut down" some

of the air goin' under the boat, cause it was blowing off alot, and after several of

those I was buyin' another boat to Mod. The third boat I did the "rocker"and also

created these fairly large and wide stumblin' blocks just the way that it causes the

problem that every body is talking about here. It didn't have the negative effect

that some here are talkin' about,,the boat was Big and Light,no negative effects in the corners, quite the opposite,,it cornered great. But the blocks did have a surprising effect,,and that was, the faster that boat went,,the more the Bow Layed

down; I kinda mistakenly created an inverted wing! Was told by many Dist. 8

boaters that "it was the fastest 1/4 scale they have seen" But when you push a

"plastic" 1/4 scale to over 50 mph and Do blow it off,,the landings are usually

are pretty hard on the structure. I don't know if this has to do with this "secret"

thats out there or not,, but It Was an eye opener.

 

[Mike Hughes]

Everyone. Here it is. All quotes from the "Tunnel speed secrets, from NAMBA 8" thread. Now drink horsy, drink. Rod is jsut trying to gets you guys to think.

The stumble pads were too rounded and would suck the boat down when they hit the water. Flatten them out and problem went away.

That boat had more round corners than a baseball. We changed the stumble blocks and added strips of ply to the sponson edges to sharpen them. Made a big improvement.

Rounded hydro-dynamic surfaces on any tunnel boat are the kiss of death.What is absolutely amazing to me is how many times we re-visit a subject such as rounded edges and stumble blocks on these discussion groups.

Notice the commonality?

 

[Jerry Wyss]

I'm Not Drinkin' It,,Ha uh! No Way I'm stickin' my tounge out at ya

 

[J Solinger]

I understand the point about sharp edges, that makes good sense. That gives a definite improvement for all hull types. I'm interested in ways of tuning the hull using these forces. For instance, is there a way to calculate the center of draw or pull on a given curve at a given distance from the CofG? I'm refering to the whole sponson bottom and how that effects ride attitude, how wet the hull runs and cornering. As well as removing these forces from running surfaces that you want free from the water. You know all that easy stuff you guys spent a life time figuring out. You can just give me the Readers Digest condensed version, thank you.

 

[Jerry Wyss]

I gotta nother thing, some have said that "air is like water" and "air acts like water"

and it"s "the kiss of death" and alike,,Then tell me how all of the latter "Miss Bud

Boats" have "Rounded" upper sponson surfaces and NOBODY could catch The SOB??? :huh:

 

[Slideblues]

Ok, I've been following along here, I have not commented yet cause I wanted to see what all was gonna be said first, so here goes.

Agree fully on the rounded edges, but how this relates to large gains in speed ??? My last three boats are not rounded anywhere, sharp edges, chines and reduced surface areas, so while stumble blocks are good for oval, how these principles apply to SAW or top speed gains still remains a mystery.

Back to the wall @60 mph thang,

Gene

 

[Jerry Wyss]

Ok, I've been following along here, I have not commented yet cause I wanted to see what all was gonna be said first, so here goes.
Agree fully on the rounded edges, but how this relates to large gains in speed ??? My last three boats are not rounded anywhere, sharp edges, chines and reduced surface areas, so while stumble blocks are good for oval, how these principles apply to SAW or top speed gains still remains a mystery.

Back to the wall @60 mph thang,

Gene

80730[/snapback]

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Well Mister "Blow Over", Ya Just Better Go Back And Read Again! :huh: This Whole

Thing is Startin' to Sound Like The 'OL "Snipe Hunt" Thing <_<

 

[Eric Perez]

Well, I've used these tricks on my cat which is really nothing much than an inboard tunnel and this is what I did to the ride pads to keep the hull from blowing over

https://www.intlwaters.com/gallery/displayimage...album=63&pos=27

It also artificially moves the CG forward because you change the pivot point. You could consider this a built-in trim tab that would only go into play when the hull reached a relative high angle of attack. I've had my boat almost pull a wheely in front of the drivers stand and come back down to finish the race.

I have noticed that when the water is glass I can hardly brake 30MPH on the radar. Put a little chop on the water and you better hold on.

I use a continous riding surface for my spoon (much like a traditional outboard tunnel) -but my ride pad is relatively small. Boat turns very well both directions.

If someone would figure out a way of cutting the drag to free up the prop in the smooth stuff and still keep it stable going over choppy water I'm all ears...

In my case I have the flexibilty of adding steps because my hull is clasified as a B hydro and not a tunnel (not outboard).

Back to the spoon experiment... Did you notice how the angle of the spoon made a dramatic difference on the drag that you felt? Not sure if it was my grip but I may be onto something...

 

[Slideblues]

Ok, I've been following along here, I have not commented yet cause I wanted to see what all was gonna be said first, so here goes.
Agree fully on the rounded edges, but how this relates to large gains in speed ??? My last three boats are not rounded anywhere, sharp edges, chines and reduced surface areas, so while stumble blocks are good for oval, how these principles apply to SAW or top speed gains still remains a mystery.

Back to the wall @60 mph thang,

Gene

80730[/snapback]

​

Well Mister "Blow Over", Ya Just Better Go Back And Read Again! :huh: This Whole

Thing is Startin' to Sound Like The 'OL "Snipe Hunt" Thing <_<

80739[/snapback]

​

:lol: :lol: :lol: Mr Blowover!!!!

Look at a Northrop T-38 Talon, coke bottle shaped fuselage, Top of a Dumas 3.5 cowl, coke bottle shaped again, So ya add the sharp ride surfaces, reduced deadrise and smaller ride surface, 62 and poof!!! Now the arched tops like the Lynx are a step in the right direction in my opnion,

Gene

 

[Joe Reese]

You guys that run all year round have all the fun

and All I get is a boat that I get to run four months out of the year.

 

[Jerry Wyss]

Eric Perez, You'd Think that "if" there was this great secret out there that the "full

sized" boat builders would have found it! Aside from that, I think someone like

Rod Geraghty could use a good retirement,,patent it,,and sell it,,whatta they gonna

Do,,Take it to their grave? Also, I haven't seen "stumblin' blocks" on a "Full Sized

F-1", Have YOU? :huh: Man,,That was several rocks at a bee's nest h34r:

OH And Gene,,You Better Have Some Rum With The Bottles of Coke

 

[Slideblues]

Hey yea...Good idea Dude!!!! :lol: :lol: :lol:

Gene

 

[waterbug]

Mike Hughes !!!! I hear you.......!! :blink:

 

[[email protected]]

well..following this post...it looks like it's going to the grave becasue no one seems to have hit upon it.

 

[Ed Radz]

You guys need to read all these posts again. Then call Rod.

Later!

Ed Radz

 

[user 115]

Hey Jerry,

Why do you think that the full size tunnels don't have stumble blocks? Could it be that they want to bury the nose and turn sharp? It's not a good comparison as full sized boats don't just run in a circle. They need to turn and turn now.

Charley

 

[Kris Flynn]

i know, i know ;-) h34r:

 

[GTR]

Hi Guys

Not that I want to buy in to this but trying to compare model with full size tunnels is a lost cause - why? power to weight!

21 size tunnel - lets assume 55MpH - around 1/8th scale well that works out to 440MpH if they were full size. Can't say I've seen or heard of many full size that fast.

Other notable differences - yes they do want to bury the nose during corners for sharp turning, but even they have spin-outs. They also have power trim which makes on the fly adjustment of motor height and angle possible. You know this has to help get the right attitude.

Okay we all know what Bernoulli does and the effect of prasitic drag - hence full size have an angled vent accross the ride surface at around the 75% point. Ever wondered why fullsize tunnels have spray rails the full length of the tunnel? Have a look at some of the under the tunnel shots and you will see the water trying to climb up to the tunnel top. These also assist with set during cornering as they act somewhat like stumble blocks when the hull sets for turning. Coke bottle shape - little to do with drag its all about functional design - if the fullscale tunnel guys thought they could taper to a point at the rear of the fuselage you think they'd have a big fat lump of outboard hanging there - shapes just to smooth the airflow as best can be compromised.

Given the relative density differences between air and water any aero drag is almost irrelevant (like RodG stated) its all about hull/engine/prop. I'm no expert but some of this seems pretty obvious - however, I don't have the magic touch to go super fast or the time to persue it. As JD says 'Run the **** boat' and pay attention to the things that make the boat go faster - remember what you did and try and repeat it. I have no doubt that the fastest things are those that don't appear to be moving all that quick - not spectacular just efficient.

 

[Ed Radz]

Ask Rod Geraghty what that spray rail is all about.

Later!

Ed Radz

 

[Grimracer]

Just a thought..

A good way to learn about tunnel hull design is to build a boat.. You can darn well bet that both Rod (wood builder) and Tommy (Glass and Wood) darn well mastered their craft by building boats.

I was digging up a video for Gener (code name TL65+) h34r: and there is some old footage of me in my first few years of racing. The boats were slow (i thought they were fast) and looking back i can tell you that in the video i can remember specific points that light bubs started coming on. The footage is old (i had short hair) but the lesions in building were quite profound.

Grim