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Do STV�s Blow over?

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First of all I would like to thank Mr. Roark Summerford on his insightfulness toward creating this short article.

Do STVs Blow over? This is an often-asked question by someone who is considering getting into to his or her first Tunnel Hull.

For some reason the tunnel boat has sensationalized the phenomenon of blow over. We have all seen those videos where the racing-along F1 Tunnel hull, just loses it and goes up, like sheet of plywood flying of the roof rack of a mini van.

Fortunately the STV owner can rest assured that your new STV is NOT in the same league as those twin sponson ,formula one catamarans. It truly is in a league by its self and can be considered as one of the safest (if not safest) go fast rides on the lake, when driven appropriately.

Appropriately means; driving your STV flat. It is a proven that the STV flies fastest and most efficiently when the angle of attack into the wind does not exceed +/-1. That is almost dead flat when you consider this over the 19 Hull length.

Picture Shows Rick Bryck Flying his STV Euro with that +/-1° Angle of Attack

post-2-1031076427.jpg

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Part 2

Here is what has been proven.

Based on ¼ Scale model, when brought to wind tunnel testing, when positioned at +/- 1° angle of attack, the STV actually creates a greater negative pressure (pulling down) in the hull tunnel, then positive pressure (pulling up) on the deck. This means the STV actually creates a certain Ground (Water) Effect that actually sucks it to the water.

If you have ever driven an STV at say 95 mph+, you will know what I am talking about. If you adjust your trim setting accordingly, this means trimming slightly in after getting over the porpoising hump. You will actually feel what some say as,  the Nose Dropping. In actuality the transom is lifting and the boat gets this locked-in feel. It literally feels locked, as the boat just sits there and does nothing stupid. A slight glance at the gauges may also indicate an RPM increase and Speedometer decrease. Dont be dismayed by the Speedo decrease, because this will confirm your tail lift. The stern can lift so high, that your speedo pitot will rise out of the water, making your reading in-accurate (usually lower).

Also note, to get this preferred stance for your STV, your prop shaft center line will be either flush (parallel) with the water or even slightly negative.

Image shows STV flying with slightly negative trim

post-2-1031076511.jpg

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Part 3

What Model to GO FAST

So now that you are pursuing that STV ride, what model should I choose?

Certainly if you need space and want to take the family along, the Euro wins hands down.

If you want to go very fast, The River Rocket is the best contender.

If you want to go super fast, then the Mod VP 2 Seater (or 1 Seat) would be the way to fly.

Each one of these STV rides will react differently at speed due to different aero characteristics at a given speed. I have listed them in order as to preference for various speeds. In other words the Eruo is Great Go fast boat and can go very fastbut the River Rocket will be a better handler at faster or similar speeds and thus the ModVP 2Seater  would for Super FAST.

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Part 6

STV MODVP

Racemans STV ModVP 2 seater

post-2-1031076966.jpg

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Part 7

So Do they Blow Over??

For the record, there has only probably ever been one recorded incident of an STV blowing over. Although I am not sure of the details, this happened in an actual MOD VP race by a famous Canadian DriverJ.

Like anything though, safety is always paramount. Always make sure, all your safety gear is worn and you and your boat are physically fit, for hi-speed boat operation. Take your time with these boats as they do take some time to master!!!

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Cool post Anthony, I'll have to let my wife read this she is always worried about blowing over.

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Just moving this up...as there has been some talk about this lately

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THANKS TECH...

Good drawing!!

I'll elaborate a little more...

So if you extended the STV's flat bottom to the nose of the boat...

1° Translates to about 4" of bow lift off the water

2° Translates to about 8" of bow lift off the water

3° Translates to about 12" of bow lift off the water

So for very one degree the boat bow  can lift an additional 4" over 19'

I think 1 to 2° would be plenty!!

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THANKS to Greg and Helmut for this great photo of Helmut flying his Euro perfect.

Here is another Point..

Notice that a properly setup STV throws NO ROOSTER TAIL...

...It more like a powder that comes off of them. This Picture shows the powder nicely too!!!

So if you are throwing a rooster tail...you need a liitle more setup and driving time

post-2-1036598398.jpg

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The my buddy had to give it a try and I got this picture as it was in the "hump zone", and a few seconds longer... the front came down. Both were running an ET prop

post-2-1036625253.jpg

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I made a few assumptions.

1 the horizon is level, so I made a line on the edge of the water and moved it to the boat. Red line.

2 I guessed where the boats bottom was, it's underwater so a close guess.

3 assumed the slight angle of the boat not to matter too much.

Also from doing this I realized if #1 is true then your eye can be deceived from the water close to the boat.

Any way it comes out very close to 2 degrees. Assume the angled view of the boat is canceled out by the non-parallal line to the spray chine on the sponson, deviates slightly.  This is what I wanted to do the first time but didn't have the time. It could be between 1.5 and 2 though.

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Trying off the chine, still plenty of room for error.

about 3 degrees.

I was thinking about putting an inclinometer in mine.  The form would be a hose runnning back to front and angled at the front for increased accuracy.  The hose would be pierced by leads at the increments, this would light up an LED when the fluid completed the circuit.  The problem is where can I get some conductive goo?  It needs to be somewhat thick to dampen out. This is nothing more than a water level with contacts stuck into it.

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Hey Guys.

My wife ran our Pro Comp up to 97 MPH today which was no where near full throttle,  but it's the fastest she has driven it so far.

No photos though,  cause I was riding shotgun.

Randy.

post-2-1036994057.jpg

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on the Analysis TECH...Looks good!!

THANKS

and

WAY TO GO ANNIE!!

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Does this mean I'm a 10 degree person ?????

Actually I was only doing about 50 in this photo running my 29 pitch, 4 blade PowerTech Yamaha Drag copy.

Sure is a fun prop up but has too much bow lift when I'm running alone.    Midrange punch is incredible,  feels like it wants to flip over backwards.

YEEEE_HAAAA

post-2-1037075869.jpg

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Hey Randy,

Glad to see your starting to get up in the speed zone!!!

Call me as soon as you break the century mark...

Mike

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Well, I have tried at times to blow over my Euro, not intentionally of course, but stupid id as stupid does sometimes. Motor was trimmed right out of the water once at around 100 mph by my dog who layed on the floor mounted trim buttons when he ducked under the deck. Stern just kinda wiggled back and forth but front stayed put. :0

Picture below shows how much you can over trim (look at motor angle) and how much hull is out of the water, yet the boat stays set at speed.

attachment.php?s=&postid=148117

Picture above was taken at the Drags we did at Nickfest 2002. Driving like the picture shows won't get you top speed but sure un-wetted my hull in a hurry.;)

Here's how I drive now! :p:p:p

1fb802b0.gif

Nick~K

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