Quartershot-STV blowovers

[stvhelm]

and it takes even more thought about lifting off the gas when you have had enough of the stupid situation you have put yourself into it.

But damn is it a rush.

You got that right

[dez nuts]

Out of all the speed boats i have ran in my life i would say by far the stv is the safest hull to go real fast in. It is a completely different feeling when you get up into the high 120;s and into the 130;s especially with a big gearcase 120 feels very slow to me after years of running my stv 130 feels alot faster but beleive it or not when you get into the mid 130;s it feels even lighter i have been told that the speedmaster feels really good and alot safer on these boats i am sure it would make a difference just never tried it for myself i know they are alot faster with the same motor i have heard up to 10mph maybe more wish i could have tried one i have seen alot more blowovers in marige;s than i have stv;s they seam to fly alot higher than the stv does we did have a 96 collins built marige jaguer down here that ran 127 mph thats the fastest i have sean in one of those or heard of maybe not but that boat did run alot flater than most the mariges that i see maybe because we ran a hyd jackplate on it and once you wind it out you keep raiseing the jack till you lose water presure than one tap down and the boat is real flat and fast but you have to drop the motor as you slow down or it will get hot. Just my thought but i do think the stv is the fastest hull and the safest also. Dave

[Russ]

I rather like RPM Racings comments on the previous page. Having gone to 130 once in my STV, I could certainly relate to things he was talking about. I also told myself afterwords that I wasn't going there again. I believe these air entrapment MOD VP hulls are truely good for what they were meant to do originally...go pretty fast and make gut wrenching turns. I don't see these boats as the type of boats to attempt speed records with, although folks like Mike Dixon and others have driven them to some pretty fantastic speeds. Personally, I feel it's extremely dangerous but still interesting to witness until something bad happens. My cut on why they are dangerous for speed runs is that these peticular air entrapment hulls build pressure in the tunnels which increases with speed, and force a tendency to want to lift the bow more and more...this would be an example of negative speed stability. You have to reach for the trim to keep the balancing act in check, and even at that, it's a real fragile at these elevated speeds they are getting to. Not allot of margin for error or some other 'event' suddenly thrown into the balancing act to try and manage to avert disaster. A better hull design for chasing these speeds would be 3 point hydros. Their design provides positive speed stability with speed increases as the air they entrap forces the stern of the boat up instead, and keeps the two sponsons in contact with the water providing additional stability and greater margins to control things by. Anyways, interesting topic...and made me think back to my moment of high 'pucker' factor.

[baja200merk]

You got that right

KID

[Denny <><]

Good thread, you guys have given good advice and instruction to us guys who are
wanting to go fast. Hope some day i'll be posting of my 120 plus m.p.h. experience's.
I agree it's all a learning experience and having big nads to go along.

[YELLOWSS]

well said phil!!!!!!!! never been in a stv... but i know what it feels like in a ally at 110, and you better have your A game on!!!!!!!!!!!!!! the times i have been in trouble is rough water... at 110 the time you see a few waves and let out of it you have hit them... i was racing a 509 ci bbc chevy powered daytona sunday and hit some rough water.... hit so hard my alien cowl came loose and went into the drink... luckly my buddy got it just before it went under..LOL they all "can" be dangerous!!!!!!!!!!!!!!!!!

but i live for the thrill!!!!!!!!!!

[benski]

All things end up at an equilibrium...lift,thrust,drag.. how you balance those things, that is the sweet spot. And the faster one goes, the greater the risk.. we have all figured that out(or will) for our own skill level and boat. It's part of the fun! Good clean stuff!

[mirage243]

Pyro, I have to disagree with you on the fact of a Mirage getting more lift. Maybe on some but my River Racer has a tendency to drop the bow at anything over 104. This hull is completely stock the way Brad built it in '88. After speaking with him a few years back it was noted that my Mirage has a different bottom then the Jaguar and the Polecat which Im sure has alot to do with the way it runs over 104. When Brad and I spoke he noted on how the Polecat was pretty much prone to blowovers when you would get over 100. So he changed up the bottom a bit to compensate for that action. Ill try to get some pics of my Mirage bottom so it can be compared with the Jaguar and Polecat bottom.

I have one of the last two real Polecat's left, and they are not prone to blowover at 100 mph. I've been 113 mph in mine in a 1/4 mile and can prove it (not guessing, on the clocks) and I would say that the threshold for it is 115. To run these numbers you must have lot's of power to push the boat, rather than trying to just trim it real high. The boat doesn't like excessive trim, it actually seems to slow it down. The one problem with the Polecat is that the tunnel's are so shallow that it doesn't release air fast enough when you get offf the throttle, it skates something fierce.

As far as the wing theory goes, anytime you are putting downforce on the boat your slowing it down, the boat is it's own wing. You just have to figure out where the sweetspot is by trim, and then figure out how big your balls are.

[Sam Baker]

What we need is an accellerometer (i.e. what's in a Nintendo Wii controller or Apple i-Phone) that will control trim as an emergency override if the angle of the boat gets to a certain point. Not that that would eliminate the "Oh $hit, I hit a wake at 90+ MPH and am going to get wet" type of blowovers, but would help keep some from getting too close to that breaking point. Theoretically, it could be used to control trim both up and down.

[Racemore]

What we need is an accellerometer (i.e. what's in a Nintendo Wii controller or Apple i-Phone) that will control trim as an emergency override if the angle of the boat gets to a certain point. Not that that would eliminate the "Oh $hit, I hit a wake at 90+ MPH and am going to get wet" type of blowovers, but would help keep some from getting too close to that breaking point. Theoretically, it could be used to control trim both up and down.

Well that's no fun Sam. 3 things.The throttle,the trim and the conditions you run in.If you can't work #1 and #2 real good #3 will get you wet. Any tidal waterway can make a hole that can result in a bad day. That's what is fun about offshore. Changes are about constant and always on the edge if you want to win.aaaaannd $hithappens.Hate to think I got wet because my i-phone lost signal.

[aguywithabucket]

hahahahahahaha $h!t i had a good laugh on that one but i have been there wher im flying a boat quick glance down to check fule and speed and trim angle and as soon as i look up ther is some wave im about to hit lucky it was one narly tail dace flowed by a jentle stuff and a sharp 90 yea my ribs where alittle sore from the seat but i wasent hitting the water @ 90

[Scott in MN]

You just have to figure out where the sweetspot is by trim, and then figure out how big your balls are.

I can relate to that, that's the truth on any fast boat regardless of model!!!!

[Ranger976]

to blowovers would be an AOI (angle of attack indicator). All the jets I have flown in my career have had one. The AOI gives you a warning of when your approaching an imminent stall. The concept is quite simple, there's an actual weather vane on the outside of the fuselage that measures the angle of attack between the relative wind angle and the angle of incidence( the imaginary line that goes from the front to the rear of the boat in the CENTER of the wing or lift). Sensors would be mounted to measure the amount of pressure in the tunnel area would input a data computer along with the AOI data to alert the driver as he/she nears the critical point of developing lift. However, the boat whatever type it is, would have to be subject to wind tunnel testing to find out where the boat or wing starts to develop lift for determing those parameters. Now having said all this, you'd end up taking an additional hit weight wise of maybe 10-15lbs. But may allow the driver to hit NEW speeds safely without any guess work. It's obvious it can't account for a roug wave or wind gust. But with lot's and lot's of MONEY it can be done and cut down the margin of error or over/under trimming. I'm guessing the cost would be around $90-110,000. Now, who's ready to give me a deposit of 10% to start testing....

[Jimboat]

Ranger976 - i like the direction of your thinking! The usual cause of a tunnel hull blowing over is that the aerodynamic lift (very significant) increases (for any number of possible reasons) more than the hydrodynamic lift can decrease - and the result is more Lift than weight - ie: flying! This can easily happen when a hull is dynamically balanced with much of the overall Lift coming from aerodynamic lift (from deck surfaces and tunnel roof) and the rest coming from hydrodynamic lift (planing sponsons and/or centerpod). When sponson pads wetted planing surfaces are very small and generating a smaller portion of the total hull lift, the resulting increase in aerodynamic lift is too much to handle.

When the hull is at this dynamically balanced state with high aerodynamic contribution, any increase in angle of attack or inherent velocity (relative velocity) can cause an immediate blowover. This could be a wind gust or small wave hit causing increased lift. Unfortunately, the best control of reaction to these circumstances is still the driver.

[see also "How do tunnel boats fly" article]

[y2kstang]

If you combined the AOI guage and tied it into some kinard wings you may be able to get away with it as the kinard could be on an actuator and generate tremendous downforce on the nose to compensate for the excess lift. Only thing is the wings would also have to react to the boat leveling back out and stop generating downforce in order to keep from driving the nose into the water.

Although I still agree with driver awareness being the most realistic method of blowover prevention.