40,000 rpm........what's the problem

[Doug Smock]

Yes, they confiscated my gear. But, that's why I have it. Too many times I've seen guys move weight forward to keep their boats on the pond in less than perfect conditions. Not a good idea, bad things happen. However, if the weight is added right at the CG.

Strut adjustments aren't always the way to go, especially in heat racing. Conditions can change quickly and if you're an idiot like I am and race 6 or seven classes, there just isn't time. It takes only seconds to add weight before you tape up for a heat and you haven't changed the set up that you worked hard to get just right.

Just my .02 FWIW fellas. By all means do what works for you!

[Doby]

Remember when this thread was about RPM???

[kfxguy]

Jay: I understand what you're saying in regards to lift, but would you agree that lift is a function of hull design and therefore can be addressed at the bottom of the hull, topside, drive angle, etc?

Travis: If gravity is what's keeping your boat on the water, what's keeping planes in the air?

Air. Lift that is greater than the force of gravity. Think we learned that in third grade. Air and water arent the same thing. Think we learned that even earlier than third grade.

[kfxguy]

Remember when this thread was about RPM???

Well it's still filled with good info and some funny, foolish stuff too :)

[keithbradley]

Yes, they confiscated my gear. But, that's why I have it. Too many times I've seen guys move weight forward to keep their boats on the pond in less than perfect conditions. Not a good idea, bad things happen. However, if the weight is added right at the CG.

Strut adjustments aren't always the way to go, especially in heat racing. Conditions can change quickly and if you're an idiot like I am and race 6 or seven classes, there just isn't time. It takes only seconds to add weight before you tape up for a heat and you haven't changed the set up that you worked hard to get just right.

Just my .02 FWIW fellas. By all means do what works for you!

I think that's pretty reasonable, and again I am well out of my league if we're comparing heat racing setups, I'm sure.
I haven't suggested that there is no difference in comparing boats of different weights. What I did suggest is that the statement "you need the extra weight to keep the boat on the water" isn't true.
As a diplomatic measure I will say "maybe some people do". I still believe that if the boat won't go a given speed without the weight (remember I'm talking about a boat that won't stay on the water as a result of increased speed, not one that is running circles in race chop), the setup is off. Adding weight to a boat (increasing the overall weight, not changing the CG) to correct an issue that is only experienced when speed is increased is a Band-Aid for another problem that is not being addressed, whether that problem is hull design, drive setup, rudder setup, props used, etc. Can we agree there?

There is another element that Mike briefly mentioned in regards to heavy, fast boats...when dealing with extreme speeds and heavy boats, people REALLY DO take intentional steps to keep a build as light as possible, while accomplishing what the builder set out to do (hull integrity, power, etc.). Part of the reason is of course efficiency, but much more importantly (IMO) is the energy a boat carries in a crash. A 30lb boat at 100+ can be absolutely devastating, even when built to be extremely strong. I once did the calculations to compare the energy of a 25lb boat at 120mph to rounds shot from pistols, shotguns, and rifles and you might be surprised by how they compare. It is unreal just how much power is at our control in some of these boats.

[keithbradley]

Air and water arent the same thing.

Ok, Gotcha. Carry on then.

[Shooter]

While we are on the lift subject (sorry for off-topic kfx), I'm starting to think that the geometry of most of the hydro hulls we run have too much lift. I think Brian Blazer was onto this with the vents on the whiplash. They seem to reduce lift by creating more flow area 'out' than 'in' (i.e. less pressure trapped underneath). The faster we get these FE's, I think we need to start making geometrical changes to reduce lift, and then require less weight/trimming to offset the lift. Just thinkin outloud after a few cold ones.

[Chrisg81983]

It always seems to amaze me how people jump on the people who can really make a difference out there. People really need to realize how a boat works, and how it ends up staying on the water. To be honest in a saw setup weight is not the thing that makes it happen. If adding weight to your boat solves your problems you overlooked something else more important , and its just a bandaid. So for people that can't come withing 50mph of what others do they need to back down and listen and stop trying to teach. My fastest best running boats were the lighter ones. Hmmmm get that the only time i added weight was to correct a wacked out cg on a boat that was built wrong by a person who didn't get it. There are many things that come intonplay that makes a good rumnig saw boat and i promise its not weight. Now I am going back to being a lurker c ya.

Oh and I can't speak for anything but SAW rules might change for oval but I am smart enough to leave that alone and leave it to the other that do know

[kevinpratt823]

Air. Lift that is greater than the force of gravity. Think we learned that in third grade. Air and water arent the same thing. Think we learned that even earlier than third grade.

Air and water are not the same, but nonetheless some analogies can be drawn from this. If a plane generates too much lift, they don't add weight to keep it from going into the stratosphere, they alter the characteristics of the lift. Personally, I tend to run heavier batt setups in boats, simply because I was sick of straining packs and I wanted some room for error. It also to an extent did help keep some of my boats on the water, but that isn't to say it couldn't have been achieved via setup and aerodynamics, but those get more complicated with very fine tuning after a certain point, and the slightest gust of wind or wave in the wrong direction seemed to negate any influence they had. I personally think it's a fine line between the two that we are chasing, but I think most setups have all the weight they need with the motor/batts selected appropriately for the purpose, beyond that it's tuning and balancing it out.

[Doug Smock]

I think that's pretty reasonable, and again I am well out of my league if we're comparing heat racing setups, I'm sure.
I haven't suggested that there is no difference in comparing boats of different weights. What I did suggest is that the statement "you need the extra weight to keep the boat on the water" isn't true.
As a diplomatic measure I will say "maybe some people do". I still believe that if the boat won't go a given speed without the weight (remember I'm talking about a boat that won't stay on the water as a result of increased speed, not one that is running circles in race chop), the setup is off. Adding weight to a boat (increasing the overall weight, not changing the CG) to correct an issue that is only experienced when speed is increased is a Band-Aid for another problem that is not being addressed, whether that problem is hull design, drive setup, rudder setup, props used, etc. Can we agree there?

Yes and no.

Hydros, Sport Hydros, Monos, Cats, O/B Tunnels all have their own issues we have to overcome as we push them to the next level.

And to complicate it further. IME with monos, things change with about every 10 MPH of speed once you get up into the high 60s low 70s.

I like what Kentley Porter told me in E City a few years ago. He said, "I finally threw all of the theory out the window and started doing what works" Kentley could set a record with a 8' 2x4 if there was a class for it. I get tired of typing his name.

Yes the power in some of these boats is incredible. I have broken my fair share. When you get into the upper 80s they don't just hit the pond once! LOL And if they stuff. We have precious few attempts to get the work done.

Again, do what works for you fellas.
I'm going to leave this for the resident experts now.

[kfxguy]

It always seems to amaze me how people jump on the people who can really make a difference out there. People really need to realize how a boat works, and how it ends up staying on the water. To be honest in a saw setup weight is not the thing that makes it happen. If adding weight to your boat solves your problems you overlooked something else more important , and its just a bandaid. So for people that can't come withing 50mph of what others do they need to back down and listen and stop trying to teach. My fastest best running boats were the lighter ones. Hmmmm get that the only time i added weight was to correct a wacked out cg on a boat that was built wrong by a person who didn't get it. There are many things that come intonplay that makes a good rumnig saw boat and i promise its not weight. Now I am going back to being a lurker c ya.

Oh and I can't speak for anything but SAW rules might change for oval but I am smart enough to leave that alone and leave it to the other that do know

I'd like to see you build a fantasm. Cut the weight as much as possible (say get it to weigh 5lbs, not possible I know) and see if you can hit 100mph with it. Then build one at normal weight and try again. Come back and tell me how your test went. I'm no dummy, i dont even have to do it to tell you what's going to happen. You have to have a certain amount of weight for anything. It's a balance.

To the person about the plane, I'll say it again, it's not the same thing. You have controls on a plane that you can change all sorts of things on the fly. On these boats, we do not. If we had remotely adjustable struts and a remotely adjustable spoiler on the front, you could keep the lightest boat on the water provided you can adjust things fast enough at speed without making it submarine or fly of the water. So ....as an easier fix, some times the faster you go, you may need to add more weight. Say or think whatever you like but the fact of the matter is most of our boats are heavy anyway once all the gear and electronics is installed so you may be heavy enough to not have to add anything anyway. Once things like batteries start getting even lighter and motors/esc's get lighter, you'll see that you'll have a harder time keeping it on the water.

[Rocstar]

I'd like to see you build a fantasm. Cut the weight as much as possible (say get it to weigh 5lbs, not possible I know) and see if you can hit 100mph with it. Then build one at normal weight and try again. Come back and tell me how your test went. I'm no dummy, i dont even have to do it to tell you what's going to happen. You have to have a certain amount of weight for anything. It's a balance.

To the person about the plane, I'll say it again, it's not the same thing. You have controls on a plane that you can change all sorts of things on the fly. On these boats, we do not. If we had remotely adjustable struts and a remotely adjustable spoiler on the front, you could keep the lightest boat on the water provided you can adjust things fast enough at speed without making it submarine or fly of the water. So ....as an easier fix, some times the faster you go, you may need to add more weight. Say or think whatever you like but the fact of the matter is most of our boats are heavy anyway once all the gear and electronics is installed so you may be heavy enough to not have to add anything anyway. Once things like batteries start getting even lighter and motors/esc's get lighter, you'll see that you'll have a harder time keeping it on the water.

You must have a lot of experience on this subject. At what speed are you personally having to add weight to your SAW boats? I haven't had to add forward weight on any of mine yet. My Fantasm did blow over, but after a stinger and cg adjustment it was flying level again...but that was only at 93 mph... I assume you're having issues at much higher speeds with yours.

[kevinpratt823]

When a boat comes off the water, 9 times out of 10 it was air, not water, that did it. That is why we call it a blow over. So yes, aerodynamics is very relevant, just so happens a plane operates solely on aerodynamics, of course they can be adjusted on the fly.

I also used the term "analogy"
n. noun

Similarity in some respects between things that are otherwise dissimilar.

[TheShaughnessy]

So yes, aerodynamics is very relevant, just


.

Aerodynamics are relevant.

My boats aren't fast enough to argue about so ill be the grammar
police.

Very is a crapy verb so I don't use it

Plural noun uses plural verb to be

[flraptor07]

I'm going to have to disagree on the Air and water not being the same thing, from a aerodynamic standpoint Air and Water are the same. I.E. Water tanks and dye to test flow chartaristics on everything from Cars to Planes to Boats to Semis. All the same principles apply.

[kevinpratt823]

Aerodynamics are relevant.

My boats aren't fast enough to argue about so ill be the grammar
police.

Very is a crapy verb so I don't use it


Plural noun uses plural verb to be

OK grammar cop, first of all, crappy is spelled with 2 p's, and you also missed a period at the end of both your last sentences. I'm sorry if I didn't use your favorite words, or proofreed my post on an internet forum as though it were a job application. I do however see that I used the word "is", instead of "are". Sorry if that upset you. FWIW, maybe some of us are fond of the word "very", it is a perfectly good adverb(not verb) you could be using to describe adjectives like "relevant", which could together describe a noun that is plural in construction, but not necessarily plural, such as aerodynamics. Using the word "is" as opposed to "are" in front of aerodynamics IS proper grammar. Go ahead and google "aerodynamics is" and see how many proper sentences come up, like
"Aerodynamics is the study of forces and the resulting motion of objects through the air." It doesn't say Aerodynamics "are the studies", hmmm.

BTW, thank you for forcing me to double check myself, reaffirming the notion that even when leisurely typing I still typically revert to using proper grammar, now could I have those 15 minutes of my life back? Perhaps you should go back to Grammar Police Academy, before you get brought up on charges and stripped of your badge

[iridebikes247]

strut angle and again strut angle. My friend and I did a strut angle experiment with a perfect running 95 mph hpr, took off like 5mm of negative boat was a mess, couldn't even get into full throttle. Trim adjustment, back to normal.

I can make my mhz 138 which is a low 90s boat run awesome on the rear ride pad....or can put in so much negative that it rides wet and flops side to side and crashes can't even get into full throttle.

When you get moving pretty fast like in the 90s, in my opinion keeping a boat on the water pass after pass with full blown WOT for a few seconds its an achievement to be proud of. All of my boats are heavy and have had serious problems because of TOO much weight in the wrong area with incorrect strut angle

Were our boats engineered to be the weight they are? not really just worked out that way. a little fightertcat hull that is cheaply made is very light but us as users have nothing to do with that, fiberglass is $.

Weight is ok but a heavy weight is boat is not like a heavy weight football player that mows down everything in site. Water is a strange element that is kinda a big part of this equation and I can assure you that too much hull in the water will result in just as many crashes as a blow over from a poorly trimmed, far back cg. With all of this said I am testing neu 1530 1y motors on 8-10s today, compared to a "heavy," setup with tp 5850 920s and 13s per side. Weight has changed a bit but speed will not, should be an interesting day.

---I might add the cool thing about these boats compared to other rc stuff, the water will sometimes let you run as you've calculated you will or it won't. There is no one answer its an art getting a boat to fly across water at high speeds. You're flying across the water and doing what you can to prevent a crash and keep it running reliably. What works today may not tomorrow and that is why even the smartest guys I know have to "think," about this stuff.

[don ferrette]

Yes and no.

Hydros, Sport Hydros, Monos, Cats, O/B Tunnels all have their own issues we have to overcome as we push them to the next level.

And to complicate it further. IME with monos, things change with about every 10 MPH of speed once you get up into the high 60s low 70s.

I like what Kentley Porter told me in E City a few years ago. He said, "I finally threw all of the theory out the window and started doing what works" Kentley could set a record with a 8' 2x4 if there was a class for it. I get tired of typing his name.

Yes the power in some of these boats is incredible. I have broken my fair share. When you get into the upper 80s they don't just hit the pond once! LOL And if they stuff. We have precious few attempts to get the work done.

Again, do what works for you fellas.
I'm going to leave this for the resident experts now.

Actually everything changes every 10mph regardless. Something a guy named Finch told me many moons ago......

And yes it gets ugly the higher the speeds get when things don't go right. Just ask the guys who were there at E-City record trials a few years ago and watched my twin nitro SAW rigger disintegrate after the rudder blade ripped off right at the end of the traps....

[don ferrette]

I'm going to have to disagree on the Air and water not being the same thing, from a aerodynamic standpoint Air and Water are the same. I.E. Water tanks and dye to test flow chartaristics on everything from Cars to Planes to Boats to Semis. All the same principles apply.

Aerodynamic and hydrodynamic properties are definitely not the same and need to be treated differently the faster we go. One of the things many years of record trials have taught me......... and my wallet.

And getting back on the rpm topic........... same holds true for heat racing vs. record trials. I approach each differently when it comes to how fast I'll spin a prop.

[keithbradley]

Aerodynamic and hydrodynamic properties are definitely not the same and need to be treated differently the faster we go. One of the things many years of record trials have taught me......... and my wallet.

And getting back on the rpm topic........... same holds true for heat racing vs. record trials. I approach each differently when it comes to how fast I'll spin a prop.

Mmm...I would like to hear further clarification of this. Both are considered fluid dynamics in the physical world and outside of gas/liquid clarification one could argue that they're synonymous.
The density of water and air may be different, but the density between hydrogen and oxygen are also different. Both are still gaseous, categorizing their dynamics as "aero".

Also, unless you're only running submarines, it might be wise to consider the effect of air on your hull. It's an essential component to making a fast boat run correctly.

To the poster that said "lift" makes an airplane fly, a less ambiguous answer might lead you to the watering trough a bit quicker. If you understand WHY an airplane creates lift, or why an F1 car will stay on the track better than a much heavier school bus, you can and absolutely should apply that to boats. There's a reason the guys that are trying to set the full scale boat speed records hire aeronautical scientists and engineers.

[kfxguy]

This thread seems to have been brought back to life lol. Pretty entertaining too!

Keith and joel, i keep waiting for you guys to post some stuff that will just blow my hair back making me look like and idiot but you guys just keep disappointing me. Correct me if I'm wrong but lift created in air and water are not the same. Air travels across a wing and meets at the rear going Two different speeds causing lift. Water doesn't travel over and under a hull does it?

This thread reminds me of the times when my son would ask me or my wife if we like bacon when he's getting fussed at to change the subject. It would work with my wife but I caught on the first time he tried it. Too funny how people get do side tracked just to try and impress people with with they know or think they know. I'm guilty of it too but I don't carry the arrogance that some people do. They are just "full of themselves", if you know what I mean.

[kfxguy]

Mmm...I would like to hear further clarification of this. Both are considered fluid dynamics in the physical world and outside of gas/liquid clarification one could argue that they're synonymous.
The density of water and air may be different, but the density between hydrogen and oxygen are also different. Both are still gaseous, categorizing their dynamics as "aero".

Also, unless you're only running submarines, it might be wise to consider the effect of air on your hull. It's an essential component to making a fast boat run correctly.

To the poster that said "lift" makes an airplane fly, a less ambiguous answer might lead you to the watering trough a bit quicker. If you understand WHY an airplane creates lift, or why an F1 car will stay on the track better than a much heavier school bus, you can and absolutely should apply that to boats. There's a reason the guys that are trying to set the full scale boat speed records hire aeronautical scientists and engineers.

An airplane is not a boat and neither is an f1 car. And f1 car stays on the track because of down force and mechanical traction, no? You can add down force to a boat and yes it will help.....I'm just going to stop right here, and stop wasting my time. Keith and joel, you guys know everything there is to know about everything. Here's your award guys. You guys deserve it!

[TheShaughnessy]

Aerodynamics is the study of forces and the resulting motion of objects through the air.

here the study of aerodynamics is the subject. Study is singular so a singular, "is" is used as it should be. Aerodynamics is plural so you still should have used "are".

I have a very large boat.
I have an extremely large boat.
I have a mammoth sized boat.
I have a boat that is gargantuan in size. Pick the one that brings the most colorful image to mine, I can assure you "very" isn't the common choice. I don't care that you use it, but it was something a college professor told me about and I tend to agree with it.

you are mistaken I'm not upset at all, just something I notice.

You are welcome, I don't feel the 15 minutes you spent were a waste at all, you expanded your brain so nothing to be upset about.

Sure this isn't a formal essay or a novel, but that doesn't mean we can't type with some accuracy.

Nothing personal, I had no comments on the other issues so I needed to type something, that's what came out.

[keithbradley]

This thread seems to have been brought back to life lol. Pretty entertaining too!

Keith and joel, i keep waiting for you guys to post some stuff that will just blow my hair back making me look like and idiot but you guys just keep disappointing me.

I don't think any of us (not sure why you single out myself and Joel) need to do that. People don't make other people look like an idiot...that's an inside job.

Correct me if I'm wrong but lift created in air and water are not the same. Air travels across a wing and meets at the rear going Two different speeds causing lift. Water doesn't travel over and under a hull does it?

Is this a serious statement?

[keithbradley]

An airplane is not a boat and neither is an f1 car.

How is this a relevant point? Please explain to me how air knows the difference. I'm here to learn.

And f1 car stays on the track because of down force and mechanical traction, no? You can add down force to a boat and yes it will help...I'm just going to stop right here, and stop wasting my time.

Good idea. you've literally brought nothing whatsoever to the table in this discussion outside of immaturity and diversion tactics when you realize you're wrong. I'm afraid it's not your time that is being wasted.

[kevinpratt823]

"Sure this isn't a formal essay or a novel, but that doesn't mean we can't type with some accuracy."

Yet in the process of pointing out a debatable phrase, you skipped two periods, misspelled a word, and called an adverb a verb...........
The noun Aerodynamics refers to the study of the aerodynamic functions, the study was the subject. The word aerodynamics has a definition all by itself, it is not a plural of the adj. aerodynamic.

[Doug Smock]

Guys, go run some boats!

I'm going to turn some rudders upside down and go do some testing.

Enjoy the remainder of your afternoon.