effects of curved and straight tub bottoms

[anthony_marquart]

The Bernoulli effect would seem to have the effect of holding a curved tub to the water and making it difficult to launch.

I have some ideas but I would like to hear your thoughts on the effects of flat bottom tubs in comparision with curved bottom tubs.

Thanks guys.

 

[Dan_Cousin]

The Bernoulli effect would seem to have the effect of holding a curved tub to the water and making it difficult to launch.

I have some ideas but I would like to hear your thoughts on the effects of flat bottom tubs in comparision with curved bottom tubs.

Thanks guys.

When I ran flat bottom hulls I found the launch is little more difficult with the prop slipping. I now run a slight curve

Flat bottoms make it easy to set tub attitude though.

 

[Geraghty]

The Bernoulli effect would seem to have the effect of holding a curved tub to the water and making it difficult to launch.

I have some ideas but I would like to hear your thoughts on the effects of flat bottom tubs in comparision with curved bottom tubs.

Thanks guys.

You are a graduate mechanical engineer,you already know the answer to your own post. <_<

There is no theory here,just simple physics."The spoon tells it all."

Look at the complete hydrodynamic picture of a rigger.

If the bottom of the tub is curved and the front sponson bottoms are curved and the rear sponson bottoms are curved,there is Bernoulli everywhere,that is only overcome buy a hell of a toss on the launch.

If the design of the tub and "all" the sponsons are correct,a launch is nothing more than just dropping the boat in the water and it will drive away.

Once you have that,the rest is all just set-up.

 

[anthony_marquart]

engineer yes,.. but I still believe that no matter what education we have there is some experience out there that is better.

Long flat running surfaces with clean, sharp breaks at the trailing edges...

The Bernoulli effect would seem to have the effect of holding a curved tub to the water and making it difficult to launch.

I have some ideas but I would like to hear your thoughts on the effects of flat bottom tubs in comparision with curved bottom tubs.

Thanks guys.

You are a graduate mechanical engineer,you already know the answer to your own post. <_<

There is no theory here,just simple physics."The spoon tells it all."

Look at the complete hydrodynamic picture of a rigger.

If the bottom of the tub is curved and the front sponson bottoms are curved and the rear sponson bottoms are curved,there is Bernoulli everywhere,that is only overcome buy a hell of a toss on the launch.

If the design of the tub and "all" the sponsons are correct,a launch is nothing more than just dropping the boat in the water and it will drive away.

Once you have that,the rest is all just set-up.

 

[Geraghty]

engineer yes,.. but I still believe that no matter what education we have there is some experience out there that is better.

Long flat running surfaces with clean, sharp breaks at the trailing edges...

OK,you know what the answer is,now all you have to do is learn how to apply that answer.

Make the bottoms of the sponsons[front & rear] and tub contours shaped with a series of straight flat surfaces with overhang and The Bernoulli principle will be assasinated in its tracks.

 

[anthony_marquart]

aaaa Thank you honorable teacher!!! (kidding of course,... a little cautious with kig joking here)

Really,... thanks

engineer yes,.. but I still believe that no matter what education we have there is some experience out there that is better.

Long flat running surfaces with clean, sharp breaks at the trailing edges...

OK,you know what the answer is,now all you have to do is learn how to apply that answer.

Make the bottoms of the sponsons[front & rear] and tub contours shaped with a series of straight flat surfaces with overhang and The Bernoulli principle will be assasinated in its tracks.

 

[VinceB]

I'll be the first to admit that "Professor Rod" is correct. The Deere Hunter has a set of his SMF sponsons and the tub has been modified to his specs.

I can drop the boat in the water and it takes off like I threw it. I can bring it OFF PLANE and motor around the course until it is time to go and when I ask - I is gone.

Many people looked at the sponsons ands said they will not work - but they could not caught me around the pond.

Yes the motors were out of synch - inboard motor starving for air - causing the boat to steer right. But I could drive out of it and still make time -

THANK YOU ROD AND DAVID

 

[Steve P]

engineer yes,.. but I still believe that no matter what education we have there is some experience out there that is better.

Long flat running surfaces with clean, sharp breaks at the trailing edges...

OK,you know what the answer is,now all you have to do is learn how to apply that answer.

Make the bottoms of the sponsons[front & rear] and tub contours shaped with a series of straight flat surfaces with overhang and The Bernoulli principle will be assasinated in its tracks.

Rod Your drawing makes it very clear on what the bottom of the sponson should be like. Just wondering about your thoughts on the top side. You drawing has an arch or domed shape is there and advantage over a flat top.

Thanks

 

[Geraghty]

engineer yes,.. but I still believe that no matter what education we have there is some experience out there that is better.

Long flat running surfaces with clean, sharp breaks at the trailing edges...

OK,you know what the answer is,now all you have to do is learn how to apply that answer.

Make the bottoms of the sponsons[front & rear] and tub contours shaped with a series of straight flat surfaces with overhang and The Bernoulli principle will be assasinated in its tracks.

Rod Your drawing makes it very clear on what the bottom of the sponson should be like. Just wondering about your thoughts on the top side. You drawing has an arch or domed shape is there and advantage over a flat top.

Thanks

Steve,How the hell are ya???Are you and your brother going to get back into this madness??

The top arch I showed in the sketch was just a quick stroke with Sharpie on a piece of posterboard just to show an approximate profile of a sponson.

The bottom or riding surface of the sponson is what I was trying to show.The top was just the result of a quick Sharpie stroke.

I try to design in a bit of downforce into sponson aero design.I also try to design a sponson back that reduces eddy currents at the back.Does this work......I really don't have a clue.

 

[RodneyPierce]

engineer yes,.. but I still believe that no matter what education we have there is some experience out there that is better.

Long flat running surfaces with clean, sharp breaks at the trailing edges...

OK,you know what the answer is,now all you have to do is learn how to apply that answer.

Make the bottoms of the sponsons[front & rear] and tub contours shaped with a series of straight flat surfaces with overhang and The Bernoulli principle will be assasinated in its tracks.

Rod Your drawing makes it very clear on what the bottom of the sponson should be like. Just wondering about your thoughts on the top side. You drawing has an arch or domed shape is there and advantage over a flat top.

Thanks

Steve,How the hell are ya???Are you and your brother going to get back into this madness??

The top arch I showed in the sketch was just a quick stroke with Sharpie on a piece of posterboard just to show an approximate profile of a sponson.

The bottom or riding surface of the sponson is what I was trying to show.The top was just the result of a quick Sharpie stroke.

I try to design in a bit of downforce into sponson aero design.I also try to design a sponson back that reduces eddy currents at the back.Does this work......I really don't have a clue.

Rod, sorry I havn had time to call you and discuss this, I am out of town for work right now, so its hard to get anytime, working 60+ hours a week, im sure you understand. Now you have given me a totally different approach to sponson building, but I have more questions now! haha, thanks man, will call you as soon as I get a chance, Rodney Pierce

 

[tnrcboatracer]

I think it is more correct to say that you aren't killing bernoulli so much as allowing the flow to detach from the surface at the steps. Full size monos adopted this technology about 10 years ago. Unfortunately IMPBA rules don't allow steps on monos. The flow separation is a huge drag reduction on the wetted surface. If you put steps on the back of your spoon, the flow would detach the same as it does on a hull. Now that the secret is out, we should see some interesting deswigns next year..........

Jon

 

[Geraghty]

I think it is more correct to say that you aren't killing bernoulli so much as allowing the flow to detach from the surface at the steps. Full size monos adopted this technology about 10 years ago. Unfortunately IMPBA rules don't allow steps on monos. The flow separation is a huge drag reduction on the wetted surface. If you put steps on the back of your spoon, the flow would detach the same as it does on a hull. Now that the secret is out, we should see some interesting deswigns next year..........

Jon

Jon,Give me your phone number.... [email protected]

Thx,Rod

 

[waltr]

I think it is more correct to say that you aren't killing bernoulli so much as allowing the flow to detach from the surface at the steps. Full size monos adopted this technology about 10 years ago. Unfortunately IMPBA rules don't allow steps on monos. The flow separation is a huge drag reduction on the wetted surface. If you put steps on the back of your spoon, the flow would detach the same as it does on a hull. Now that the secret is out, we should see some interesting deswigns next year..........

Jon

Steps are really no secret at all.Full sized boats have been doing this for decades.

Our 1st Skater Cats have had steps since 1980 and just look at the bottoms of Reggies Fountains or the Formula Fast techs.Steps have been incorporated for some time now.Nothing new.

But the trick is to have them properly placed,proper depth and angles.If done incorrectly the boat will be a handling nightmare.I've seen my share of people pitched from full sized monos because of step problems.

Just like everything else,there's developement work to be done to get it right.

 

[John Finch]

I have a huge box of sponsons in the attic that I used to experiment with aerodymanics on my riggers. I think I'm getting a handle on what's what, but I only have one set that has the flat angles in Rod's drawing. It worked up to a certain speed then the boat blew off the water, but the reason was later found to be how the air leaves the sponson that caused the lifting at high speed. I think the trailing edges are more important than the riding surface for controling lift.

 

[El Zorro]

Very interesting topic..........gives me a few ideas to try on my next C Stock hydroplane ( if the kit ever gets here! ) that I plan to build over the Winter.

I ran across an interesting web site having to do with tunnel boats ( okay, Im a little off topic ) that is very informative and deals with boat design, performance, etc. Go to "http://www.aeromarineresearch.com/index.htm". The big boat stuff is not much different than the little boat stuff.

Thanks for sharing your knowledge with us, Rod.

I have seen in person John's box of sponsons...........sorta like a "junkyard in a box"..........neat stuff. You pick one up to look at and ask " why is this like that?" and you get an answer...........

Dick Tyndall