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???
Printable View
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???
nature of the beast,just drive through it!
so its not trim???
Its 0 to 100+ forget everthing inbetween.
A slight porpoise is normal, Mine did it too.
Chris
All tunnels have a point where this happens, some more pronounced than others. Go to www.aeromarineresearch.com and look for articals written for magazines, I believe Jim did one for Hot Boat mag. His book Tunnelboat design is worth getting and explains it well.
Dave
In short; Bernoulli's principle's. If you understand these principle's, you will understand WHY your boat or anything on water does what it does. I find it amazing that this 18th century mathematician understood fluid dynamics that boat companies dont care to study.....When people start building boats according to these principle's and Bernoulli's equation, these bad characteristics will dissappear and boats will be going a lot faster.
Jr.
Basically this is the point at which your boat is generating enough lift to start to free the boat up, but as soon as it comes up, it spills the air from the tunnels and now doesn't have enough lift anymore, to keep it flying. Depending on the weight of the boat and the weight in the boat, this will shift around by up to 10mph. Pointing into or away from the wind will affect it too. As mentioned, drive faster or slower to avoid it, but it will always be there if you try to cruise or slowly accelerate through that range.
Your post infers that the STV isn't properly designed - is that what you meant to convey? The STV design is one of the most stable, high performance pleasure boat designs you can step into. I'm not aware of any other Mod VP style hull that has gone as fast as an STV (please, someone correct me if I'm wrong here) - 151.5mph on GPS in a 18'6" long boat. WOW.Quote:
Originally Posted by Speed Jr.
No, Im conveying that the reason it bounces is very simple and can be explained. Thats all. It can be corrected. Not a big deal. Dont be so defensive, doesnt matter if an STV is designed wrong or right. It is ignorant to think it cant be improved on, cause eventually it will. I put that post up for someone who really wants to educate themselves to truly understand fluid dynamics. Sorry you took it your way.
Jr.
It will always be there, there is way more than just hydrodynamics causing the hop. Aerodynamics as Keith said gearcase drag, weight ballance, etc. Just be glad it happens at 65-75mph and not 95-100mph.Quote:
Originally Posted by Speed Jr.
Dave
:( Im sorry you feel this way. I never said anything about hydrodynamics.Quote:
Originally Posted by Dave Strong
MARCSOTO,
You asked "what is happening" referring to the bounce you are experience. It is easily explained according to these fluid dynamic principles. PM me your phone # and I will gladly read then explain to you these principles. Knowledge is power. I personally dont accept the "Nature of the beast" answer. Thats not an explaination. Does it do it? Yes it does. Can it be explained? Yes. It can be explained in books from the 1730's. Im not trying to offend anyone here, which always seems to happen when explaining something people dont understand.
Jr.
You may change it some but it will always be there just the facts of life all of them do it.
Dave
Go to www.aeromarineresearch.com get a reprint of the artical from Hot Boat called "HUMP zone", think you will find it an intresting read.Quote:
Originally Posted by Speed Jr.
Dave
What I'm worried about is blowing over. I don't have a trim gauge and just didn't know if it was on the point of it happening. What speed will the boat be in the "blowover zone", thanks guys.
Download the STV Euro report on http://www.aeromarineresearch.com/
Not trying to be a smart a$$, but why do you not have a trim gauge? STV's are not a beginner boat.
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
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?Quote:
Originally Posted by FrenchPhil
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 .
http://i55.tinypic.com/20kwqbk.jpg
make sure your skeg is not welded :):)
haha:DQuote:
Originally Posted by specboatops
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,
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
Marcsoto - not to worry, your Euro is exhibiting it's 'hump zone' at a very typical 70mph for this hull.Quote:
Originally Posted by MARCSOTO
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.Quote:
Originally Posted by Speed Jr.
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.
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.
Not Tring To Be A Smart Ass , But , I've never had a Trim gauge , in Any Boat !Quote:
Originally Posted by D.B.S
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:thumbsup:
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
Jimboat, from your research what do you think of the design of current popular boats like STV's, Allisons, etc?
Jr.
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.Quote:
Originally Posted by Speed Jr.
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.
you dont need a trim guage,the boat and motor tell you the trim if you listen and feel it
I had a Stv mod VP that never hopped, and no trim gauge. The only thing was that it was either at idle on plane or wide open. I am assuming it went through the hop zone so quickly that it just did not happen. Sure was fun!
Dutch & EuroScott both make great points re: trim gauge. it's good to have the gauge so that you can reference where the motor is set, but when you're going fast the best gauge, by far, is your experience and constant attention to what the boat is doing, how it's responding - sound, feel, behavior. 'Seat time' is really your friend for this! Hull design can always make the best of a boat/setup, but no matter what the design is, it will be possible to get into trouble if you're not paying attention. Good words to remember..."respect the speed".Quote:
Originally Posted by Dutch
That Speed Jr. is a smart fellow!!!
if you need a starting point for reference level the boat and engine on the trailer. sit in the drivers seat and look back at the engine.. look at the seam in the cowl or the sticker or whatever so you can have a ballpark reference point for starting.
Sounds like a good idea.
Dirferent props make a big difference on mine both in porposing and torque steer
There is some great info on here, and some very experienced euro drivers chiming in as well as some smart folks. I drove my euro for over a year w/o a trim gauge getting used to the feel. I bought a stainless marine trim gauge and love it for the reference. I know where to put it into the wind, where to put it with the wind, but the feel of the boat is still the best reference.
The euro is a very forgiving performance boat, you will quickly learn what it likes and does not. Yu do not need a lot of trim and with a 260 you have the power to drive through the hop. It will be there, just don't remain in the hop speed or it will continue. Gve it some gas where the hop speed is for you and you won't feel it; after the first time it comes up a little you will clear the bubble, the boat will set and no more hop.
Just a question for reference I don't intend on squeezing the juice yet, but if I floor the boat from a dead stop and at about wot I use the nitrox, will the hop also be their although my speed is increasing faster then normal? Thanks
The quicker you pass thru the transition speed zone the less noticable it will be. Thats what everyone here is trying to pass on to you either add power and push thru it or stay below it. This is gonna be something you will hardly notice as you get more seat time. Windy days are not the time to air out any of these small boats. IMO. Seems like every March we here of a blow over.
Quote:
Originally Posted by MARCSOTO