why does my euro bounce at 70 mph?

[D.B.S]

Not trying to be a smart a$$, but why do you not have a trim gauge? STV's are not a beginner boat.

[Chummy]

I think the boat is defective..... better sell it If you don't have a trim gauge, you need to get used to the way the boat feels so that you know what is right or wrong

[Speed Jr.]

Download the STV Euro report on http://www.aeromarineresearch.com/

The third paragraph of this article is spot on with the Aerodynamic lift of the tunnel and the Hydrodynamic lift of the running pads. What the article didnt consider is the effect of compressing air, which changes the speed in which the air flows through the tunnels. This creates or releases drag, and that my friends is Fluid Dynamics (Compressible flows principle).....Has anyone here tried an Air Defuser on their tunnels?

[Tom Foley]

You will not blow it over at 70 or even 75 . When I first got mine I thought the same thing , they all have a trim / speed point where they have not dumped the trapped air and they porpoise . Trim a little higher while applying throttle and easing wheel to the right and when you feel it stop porpoising , bump a little down trim . Mine likes 65 MPH or 75 MPH or faster , not 70 .

[specboatops]

make sure your skeg is not welded

[MARCSOTO]

make sure your skeg is not welded

haha

[Davey W]

Be more worried about the stuff then the blowover,the faster you go the the more down forse on the nose of a euro,what motor height are you running,with a little common sence you will never blow that thing over,Oh and get a trim gauge,0 trim will work just fine for ya,add a little if needed,,,and do what Tom says,you will be fine,,,take your time and were your lifeline,stay safe,

[joed]

All tunnels I ve driven do this a some speed The hull is in transition from a displacement type situation to packing air ( ground effect) along with the airfoil shape of the upper deck creating lift. The bernuli principle as mentioned above. In effect its going from a boat to a low flying plane. This hop will move to a higher speed with a heavier load just like th V speeds on and airplane have to be adjusted for increases in gross weight. I call this it doing the Linburgh, if you `ve ever seen the footage of his grossly over loaded plane hoping as it started out for Paris. I bet there was an oh **** every time it touched back down. Power thru it or stay under it and buy all means get a stainless marine trim indicator.

Good luck

[Jimboat]

i have a 93 euro with a 260 and im runing an et 30...... what is happening that the boat starts to bounce around 65 or 70???

Marcsoto - not to worry, your Euro is exhibiting it's 'hump zone' at a very typical 70mph for this hull.

The third paragraph of this article is spot on with the Aerodynamic lift of the tunnel and the Hydrodynamic lift of the running pads. What the article didnt consider is the effect of compressing air, which changes the speed in which the air flows through the tunnels. This creates or releases drag....Compressible flows

All performance hulls, and particularly tunnels, will progress through what we call the "hump zone". This article "hump zone" briefly explains some of the principles that contribute to this zone of dynamic instability. And yes, all performance boats will exhibit a 'hump zone' - some more pronounced than others.

The deck surface and tunnel roof of a tunnel boat form a "wing" that is particularly efficient at generating lift for a performance hull. This "wing" is operating in what is called "ground effect". There is really no 'compressed air' in the aerodynamics of a tunnel hull. There is some explanation in this article on "aerodynamics of tunnel hulls". The onset of the "hump zone" has to do with the complex mix of aerodynamic and hydrodynamic lift & drag forces that are in play on a tunnel hull and performance vee hull. It's tricky because this mix changes at every velocity though the speed range. Some boats transition with only a minor affect on stability, others have a more dramatic feel, but all go through the transition.

There are several other articles describing performance hull design, hydrodynamics and aerodynamics on my web site. The "Secrets of Tunnel Boat Design" book explains all of it, with examples, if you're interested.

The detailed analysis of "porpoising" is somewhat complex, but is addressed here. There are some other discussons of porpoising in other threads.

Dave strong is right, all boats have a "hump zone" but there are ways to minimize the impact of the hump zone on performnance as your hull moves thourhg it's designed velocity range.

[MARCSOTO]

I'm going to the boat show tomorrow aNd getting the trim ind. I'm a pilot and I'm very familiar with weight and balance and bernulis prin. I know that its going to take some seat time to get to know my boat.

[RNM018]

Not trying to be a smart a$$, but why do you not have a trim gauge? STV's are not a beginner boat.

Not Tring To Be A Smart Ass , But , I've never had a Trim gauge , in Any Boat !
And don't think , it's a good idea to live by one .
Learn the boat , then just use the gauge , for a refferance , If you have one !


Rich Martin 018

[MARCSOTO]

Thanks jumbo, I'm going to spend sometime and study the charts you sent me. It looks like their is a lot of complex reading and understanding how the air and water react to each other. Every bit helps. Keep it coming guys. Marcos

[Speed Jr.]

Jimboat, from your research what do you think of the design of current popular boats like STV's, Allisons, etc?

Jr.

[Jimboat]

Jimboat, from your research what do you think of the design of current popular boats like STV's, Allisons, etc?

Jr. - both STV and Allison are outstanding hull designs, with several groundbreaking design features introduced by each of them over the years. Roark Summerford (STV) and Paul/Darris Allison (Allison boats) are both great designer/builders. The STV is a true 'modified vee' tunnel hull with all the aerodynamic /hydrodynamic features of a tunnel hull with center pod/pad. Both of these are very fast hulls, each with specific performance and application advantages.

[Dutch]

if you over trim a euro it will rock side to side. as long as you trim in small incriments you will never blow it over, it will blow out first. a trim gauge is nice for a starting reference, but you can't live by it. learn the feell of the boat, the only way is with seat time. just take your time and remember when you loose respect for the speed is when things get ugly.