Spedometer Mechanical/GPS

[Lawler]

Just wanted to get some info out of everyone on GPS vs Mechanical speedometers. I am not doubting anyone on this website as to how fast there boat goes but I was just curious how many of you are using mechanical speedometers compared to GPS. Only reason I ask is that a friend of mine claimed his boat went 70 MPH for the longest time. Well we finally got a chance to run the boat with a hand held GPS and he only hit 64 tops on a calm day although his speedometer said he was doing 70.
I have recentley installed all Autometer Carbon Fiber gauges in my Eliminator and I went with the GPS speedo and I love it. Gauges look sharp! I'll post pictures soon.

[Duane HTP]

If you can afford it, GPS speedometer is the way to go. They are even more accurate than the cheapie hand held ones.

[LVjetboy]

By mechanical I'm assuming you refer to pitot. Yes I've run both pitot and GPS. Despite many claims to the contrary, I've found my pitot and GPS very close. Within 2 mph...usually less.
My pitot is vdo not that that's important, but before that I had another brand (magellan) and ran both to compare, two pitot pickups on my transom, two gages from different mfgs...very close. My GPS is Garmen and I checked it against my vette digital speedo...again very close. When I ran 100 mph, the vdo pitot gage needle hovered over the 100 mph mark and the GPS satellite triangulation "gage" clicked over to 100 mph.
So I'm thinking maybe that's accurate?
Especially considering those two instruments are independent in signal and calibration and measurement technique? Just a thought.
I think pitot gets a bad rap when it comes to dock talk. Sure some are off due to installation, calibration or leak problems, but I think a lot is due to pure braggin' and dock talk. In other words, people who claim one thing but the truth is another. If you listen to dock talk and draw conclusions about instrument accuracy based on braggin' rights then maybe you'll draw the wrong conclusions?
I've also had a friend claim his jet ski did 65 pitot mph. Was his claim true? So we ran side-by-side and he ran 55 mph on my old fashion (allegedly inaccurate) pitot gage. Ruined his whole day...in fact he sold that jet ski soon after. Now I can't say his pitot calibrated wrong...I wasn't looking at it at the time, maybe he was? All I know is my mechanical gage didn't back his dock talk claims.
Bottom line: In my experience, both pitot (mechanical) and GPS (electronic) can be accurate for what we care about. Not to say that everyone's pitot is accurate or everone's GPS has a clear signal. But one of these days, I'll post pictures of my GPS mph and mechanical or pitot (vdo) mph at every 500 rpm change to dispel once and for all the myth that pitot or GPS are inherently inaccurate.
jer

[BigBoyToys]

I've ran a handheld GPS. But it didn't give me the same numbers as I had while going through the lights at Ming (NJBA Race). I'm not sure which is best, but for accuracy sake, I'll stick with the Ming numbers. :cool:

[Rexone]

BBT on GPS you gotta remember there's update time so a drag boat condition (acceleration) you are not going to get immediate accurate readings from the GPS when your talking seconds or fractions thereof. So yes I'd say the lights will be more accurate in that environment in just about every case.
I've also obtained very accurate pitot measurements in the past but as Jer mentioned installation and numerous other factors can easily affect accuracy. And some pressure speedos were very inaccurate from the factory including some high end ones we tested when we were calibrating lots of liquid filled stuff a few years ago.

[Duane HTP]

Another thing to consider on the speeds like at Ming, is that the timing clocks on a drag strip are x number of feet apart. The first sensor picks up the boat as it comes into the speed trap and starts the timer, the second one shuts it off. Because of this, you are not actually getting your top speed at the end of the course if your boat is still accelerating. You are getting a reading of the average speed over the last x number of feet. So, if your GPS OR Pitot Tube reading is extremely accurate, it will always give you just a little higher readiing than the clocks. Very techanical, I know, but still true. On R & D Express, the GPS and Computer readings were always between 1 and 1.5 mph higher than the clocks. For those of you that have computers, you can prove this fact by looking at your graphs.

[BigBoyToys]

BBT on GPS you gotta remember there's update time so a drag boat condition (acceleration) you are not going to get immediate accurate readings from the GPS when your talking seconds or fractions thereof. So yes I'd say the lights will be more accurate in that environment in just about every case.
I've also obtained very accurate pitot measurements in the past but as Jer mentioned installation and numerous other factors can easily affect accuracy. And some pressure speedos were very inaccurate from the factory including some high end ones we tested when we were calibrating lots of liquid filled stuff a few years ago.
Good point Mike!! I didn't think of that
BBT<------A Little Slow Sometimes :D

[LVjetboy]

Posted by Lvjetboy: "...Bottom line: In my experience, both pitot (mechanical) and GPS (electronic) can be accurate for what we care about. Not to say that everyone's pitot is accurate or everone's GPS has a clear signal. But one of these days, I'll post pictures of my GPS mph and mechanical or pitot (vdo) mph at every 500 rpm change to dispel once and for all the myth that pitot or GPS are inherently inaccurate."
Later BBT posted...
"Good point Mike!! I didn't think of that"
Just wondering BBT...did you take the time to read and THINK about my post? I took time and put much thought in my post. Or did you dismiss my post as someone who doesn't have experience like you think Mike has? Talk about kiss-up.
So you didn't think about what? GPS update timing or what? Freakin' brown noser.
jer

[BigBoyToys]

Posted by Lvjetboy:
Just wondering BBT...did you take the time to read and THINK about my post? I took time and put much thought in my post. Or did you dismiss my post as someone who doesn't have experience like you think Mike has? Talk about kiss-up.
So you didn't think about what? GPS update timing or what? Freakin' brown noser.
jer
No, I didn't read your post, and what Mike said made sense to me as far as the GPS updating goes when compared to the timing lights on the NJBA course.
I didn't read your post because your crap usually goes way over my head with all the charts and numbers and crap. Just say it like it is, direct and to the point and maybe I'd understand what in the hell you're trying to say better. In as much as I didn't read your post, I didn't dismiss it as anything. Maybe I'll read it and see if I can make heads or tails of it. But then again, since I'm a brown noser to you, maybe I won't read any crap that you post. I have NEVER said anything or done anything against you, but you wanna come out of the corner slinging that kinda crap. Just because I understand what Mike was saying about the GPS Updates Vs. the NJBA lights, does not mean that I'm a "Brown Noser". In fact, as you are about to find out, I'm quite independent in my thinking, and will say what I wanna say to who I wanna say it to, and will believe what I wanna believe. And let me clarify, the part of Rexone's post that I agreed with, is the GPS Vs. NJBA Timing Light deal. I did not even read the rest of Rexone's post about the other stuff, since the only thing I was interested in was the difference between the 2. I am not concerned whatsoever with the pitot, mechanical, whatever ya's wanna call it, stuff.

[BigBoyToys]

Ok Jer, I just read your post. And although you may have a point about the mechanical stuff being accurate, that is not my interest, as previously explained. While your post was primarily about the accuracy of the Pitot/mechanical deal, it would make sense that I did not read it because that was not what I was interested in. I was interested in the differences between GPS and The NJBA Timing Lights and the differences and techniques that are used to determine the speed. Hence my comment to Rexone. Like I said, my comment to Rexone was based on the first part of his post, because that is what related to what I was interested in. You did not even address that in your post so naturally, your post had nothing to offer me. I didn't see anything in your post that had anything to do with the comparisan between the NJBA Timing system vs. the GPS :rolleyes:

[BigBoyToys]

And furthermore, I used to think that you were pretty cool and had alot to offer to Jet Boaters. But after your rude comment, it's become obvious to me that you're no more than a *CENSORED* that has nothing to offer other than name calling and dysfunctional thought patterns. Talk about kiss up.... :rolleyes: :rolleyes: :rolleyes: Maybe you need to think a little before posting and realize what someone is talking about before you start slinging your slander.
Sorry 'bout that Mr. Moderator. Had to speak up. I'm done now so no need to move the topic. Carry on :D

[Jim Hall]

:idea: Since we are on the topics of speedometers, I was curious about a couple of things. One is , what is the best placement for pitot tube and is there a good way to check/test operation of system?

[Lawler]

go with the gps

[Duane HTP]

Jim, the pitot tube should be placed 7" to one side or the other of the bottom center of the boat.

[Her454]

Posted by Lvjetboy: "...Bottom line: In my experience, both pitot (mechanical) and GPS (electronic) can be accurate for what we care about. Not to say that everyone's pitot is accurate or everone's GPS has a clear signal. But one of these days, I'll post pictures of my GPS mph and mechanical or pitot (vdo) mph at every 500 rpm change to dispel once and for all the myth that pitot or GPS are inherently inaccurate."
Later BBT posted...
"Good point Mike!! I didn't think of that"
Just wondering BBT...did you take the time to read and THINK about my post? I took time and put much thought in my post. Or did you dismiss my post as someone who doesn't have experience like you think Mike has? Talk about kiss-up.
So you didn't think about what? GPS update timing or what? Freakin' brown noser.
jer
jer, are you not getting enough attention at home or what? WTH is with your posts? I ran a search on all your posts within the last year = 12.0 months and I came up with a formula that is equivalent to about 180mph, proven with a plastic toy gps held by a 4 year old in the back of a 1970's jet boat that needs serious impeller work.
The formula includes approximatly 156 posts in the 12.0 months that are filled full of anger, rudeness and general offensiveness. Out of these 156 posts not one single target of your insults initiated the travesty of bullshit you call information.
96 of these posts within a 3 month period, all posted between the hours of 2am and 6am, at the rate of 86 keystrokes per minute, were so utterly confusing that they really in fact didnt even count.
36 of those 156 posts were apparently meant in some sort of deranged sick sense of humor that only one can appreciate at the hours of 2am and 6am.
12 of those total posts included your swift ability to insult almost any type of personality on the board in regard to family, life, children...just about anything passionate to someone else that you choose to destroy with your humble opinion.
The remaining 12.0 posts in that 12 month period consist of your quest to abolish the imaginary Rexone Tyranny of the ***boat Forums and censorship in general. I can honestly say that I never know from one day to the next what to expect from your posts except the consistent negativity.
Thank you for your contribution to ***boat.
I apologize in advance if I've offended anyone with my post.

[Marlin455]

Her454- Please don't hold back- Tell Jer how you really feel!LOL- Actually, I agree with you her454- I lurk most of the time, but have seen some pretty negative stuff from jer- Reminds me of my alcoholic brother.
Stan

[Jordy]

Now that's funny right there. C'mon. :D :D :D
T, I'm sure that there will be some charts and a couple of graphs posted up by tomorrow morning to disprove your theories though. :D

[Her454]

Now that's funny right there. C'mon. :D :D :D
T, I'm sure that there will be some charts and a couple of graphs posted up by tomorrow morning to disprove your theories though. :D
I'm sure. :rollside:

[BigBoyToys]

jer, are you not getting enough attention at home or what? WTH is with your posts? I ran a search on all your posts within the last year = 12.0 months and I came up with a formula that is equivalent to about 180mph, proven with a plastic toy gps held by a 4 year old in the back of a 1970's jet boat that needs serious impeller work.
The formula includes approximatly 156 posts in the 12.0 months that are filled full of anger, rudeness and general offensiveness. Out of these 156 posts not one single target of your insults initiated the travesty of bullshit you call information.
96 of these posts within a 3 month period, all posted between the hours of 2am and 6am, at the rate of 86 keystrokes per minute, were so utterly confusing that they really in fact didnt even count.
36 of those 156 posts were apparently meant in some sort of deranged sick sense of humor that only one can appreciate at the hours of 2am and 6am.
12 of those total posts included your swift ability to insult almost any type of personality on the board in regard to family, life, children...just about anything passionate to someone else that you choose to destroy with your humble opinion.
The remaining 12.0 posts in that 12 month period consist of your quest to abolish the imaginary Rexone Tyranny of the ***boat Forums and censorship in general. I can honestly say that I never know from one day to the next what to expect from your posts except the consistent negativity.
Thank you for your contribution to ***boat.
I apologize in advance if I've offended anyone with my post.
Now THAT is funny :wink: ROFLMAO!!! Great Post Traci!!! :wink: :D

[Old Guy]

Probably nobody cares, but I'm gonna post this anyway. About 20 years ago, I wondered about the bad rap that was given boat speedometers so I called Teleflex (my boat had a Teleflex speedo) and asked the question. I talked to a very nice fella who was very helpful. He said that back in the '60's and '70's the boat manufacturers (many, but not all) required speedometers that showed a speed that was faster than actual. Of course, they could make the thing read about whatever the customer wanted. If you wanted to sell your product, you gave the boat manufacturers what they wanted. After market speedometers were always made to read as accurate as practical. This explains a lot.
He supplied the following info for anyone wanting to bench calibrate (or check) any boat speedo.
mph = psig
20 = 5.3
25 = 7.46
30 = 10.9
35 = 14.8
40 = 19.36
45 = 24.5
50 = 30.25
60 = 43.56
Of course, you would need a very accurate gauge as a master reference

[BigBoyToys]

Good stuff!!! :D

[TX19]

Do you think I could send my Nordskog in for recalibration. I'm sure it is about 20 mph slow - the same amount my GPS is off. :smile:

[LVjetboy]

Just to stay on track...Lawlers first post to this thread... "Just wanted to get some info out of everyone on GPS vs Mechanical speedometers." I'm thinking from his reference to a friends claim vs. handheld GPS he wanted to know why the difference? Implied was top speed, as in no acceleration, just top speed. Or that Lawlers post was based on the 1/4 mile, racing or et.
Duane and LVjetboy first responded to Lawlers post.
Then BBT modified the original thread by questioning his experience with the timing lights at ming citing his 1/4 mile mph not equal to his gps mph.
Both Rexone and Duane posted possible errors in BBT's 1/4 mile acceleration mph versus steady state GPS measurements.
Both good posts by Rex and Duane.
Then LVjetboy responded to BBT's post...citing again the accuracy of steady state GPS compared to pitot, which after all was the original issue posted by Lawler, not BBT. Obviously, steady state pitot vs GPS different than acceleration pitot vs GPS because of update delay. But then who reads pitot accurately at the lights? Are you reading that gage or focusing on the track? And BBT said he didn't even read my first post, although I've cited GPS update errors in the past on this board and others...maybe if you read my posts BBT? Sorry if I assumed you've read my posts on this thread or in other GPS threads in the past.
Her454, "Blah, blah, blah...thank you <jer> for your contribution to ***boat."
You're welcome Her454. Maybe some actually read and welcome my comments, even if a bit controversial. Either way, I take no offense.
jer

[LVjetboy]

Old guy, I still have that from your original post. Even though your data may be boaring to some, at least it's information not bs.
BBT, you got information not bs?
My point, if GPS matches Vette speedo, matches boat VDO Speedo, matches Magellon Speedo, then maybe accurate?? That's my experience tho boaring to some such as yourself. And maybe an answer to Lawler's original post? Not that all mfg speedos are accurate as there can be a calibration error. Not that all GPS's are accurate as there can be update and signal strength error.
You say to Old Guy, "Good Stuff"
I'd agree. Sure numbers are a table of boaring data just short of a boaring chart as you may think or claim not worth reading. But Old guys post is useable data and relates more to Lawlers original question (not yours) than the superficial acceleration contradiction between 1/4 mile mph and GPS mph you mentioned. If you factor out accerleration then compare? In other words, if you're not topped out then duh? There WILL be a difference between pitot and GPS.
Your question.
But that's a given I assumed.
jer

[LVjetboy]

Marlin455, "I lurk most of the time, but have seen some pretty negative stuff from jer- Reminds me of my alcoholic brother."
Why lurk then? Why not contribute if you have something worthwhile to say about jets or tech? Or the subject of this thread?? Speak up. If you can contribute you're certainly welcome to join in. What does your sober self, or your alcoholic brother for that matter, think about Lawlers post on "GPS vs Mechanical speedometers."
Just curious? If you have anything worth contributing?
jer

[BigBoyToys]

Jer,
No worries man.....Just to clarify, no, I have not read your posts in the past on GPS or on the pitot thing. Actually, I never even knew what a "pitot" was unil this thread :confused: So now I do. To be honest with you, I've never read any topics in the past about speedometers and/or GPS but since I recently got a GPS and have used it 2 times, I decided to read this thread and was interested in the numbers difference between my "new" GPS and my knowledge of the numbers that I ran at Ming last year. I did not read your original post in this thread until I said I did, which was later when all of this BS started, after I was called a few select names by you. I did, however, read Rexones post, at least the first half of it anyways, as it pertained to what my interest was in this thread. Then just because you asked if I even read your post (Which I didn't originally because it didn't seem to have the info I was interested in), I went back and read your post....because you asked if I did. As it turned out, your post did NOT contain the same info as what Rexone's post did, as far as what my main interest was in this topic. SO, in the end, I ended up with a general understanding of my questions/ interest in this thread were, while at the same time, got blasted by you for not reading your post :confused: No hard feelings here on my end, just ask me next time what my concern is before attacking my character huh? :cool:
Here's an edited Add on; The Irony of this deal, is that my boat has a speedometer and one of those pitot thingys in it, but it has never worked since I've owned the boat (4 years) and I have never had any desire to fix it. It doesn't matter who's going faster, what matters is who gets there first :D :D :D :D Oh yeah, I also had a radar gun until I sold it in May, but that thing wasn't EVEN close to real numbers since the boat had to be coming straight at the gun and I couldn't find anyone that was daring enough to sit out in the middle of a lake holding a radar gun, while I was coming straight at them at top speed :eek: LOL

[Mr.&Mrs.Budlight]

Now I'm so confused LV jetboy, I don't think I can trust GPS, Mech, or Vdo. I think I'll leave my boat on the trailer, drive down I-40, wait for Smokey in the sky and get a speeding ticket for doing 100mph, check my truck speedo, have my wife read the speedo in the boat. And recieve a ticket for speeding, unsafe passenger in boat, go to court and claim I was calibrating my speedometers!!! the judge will let me go cause he was so impressed! [and he liked my wife] Budlight :idea: :idea: :idea:

[BigBoyToys]

Now I'm so confused LV jetboy, I don't think I can trust GPS, Mech, or Vdo. I think I'll leave my boat on the trailer, drive down I-40, wait for Smokey in the sky and get a speeding ticket for doing 100mph, check my truck speedo, have my wife read the speedo in the boat. And recieve a ticket for speeding, unsafe passenger in boat, go to court and claim I was calibrating my speedometers!!! the judge will let me go cause he was so impressed! [and he liked my wife] Budlight :idea: :idea: :idea:
That's funny!! :2purples: :cool: LMAO!!!

[LVjetboy]

Either that Bud or we can run?
:D :D
jer

[Her454]

Now I'm so confused LV jetboy, I don't think I can trust GPS, Mech, or Vdo. I think I'll leave my boat on the trailer, drive down I-40, wait for Smokey in the sky and get a speeding ticket for doing 100mph, check my truck speedo, have my wife read the speedo in the boat. And recieve a ticket for speeding, unsafe passenger in boat, go to court and claim I was calibrating my speedometers!!! the judge will let me go cause he was so impressed! [and he liked my wife] Budlight :idea: :idea: :idea:
ROTFLMAO! :D :D Be sure and post your ticket so we can see the numbers...some on here are non believers and require such documentation. ;)
Just to stay on track..
Her454, "Blah, blah, blah...thank you <jer> for your contribution to ***boat."
You're welcome Her454. Maybe some actually read and welcome my comments, even if a bit controversial. Either way, I take no offense.
jer
LV, There is hope for you yet. I promise I wont let it out that there is a soft side to you and when you put your mind to it you can be downright nice.....sometimes. :)

[LVjetboy]

BBT you posted: "Here's an edited Add on; The Irony of this deal, is that my boat has a speedometer and one of those pitot thingys in it, but it has never worked since I've owned the boat (4 years) and I have never had any desire to fix it. It doesn't matter who's going faster, what matters is who gets there first Oh yeah, I also had a radar gun until I sold it in May, but that thing wasn't EVEN close to real numbers since the boat had to be coming straight at the gun and I couldn't find anyone that was daring enough to sit out in the middle of a lake holding a radar gun, while I was coming straight at them at top speed LOL
There's errors in all three of course. Pitot (mechanical based on location and calibration), GPS (triangulation or positional assuming signal strength), and radar (signal timing assuming straight on or adjusted for angle) Of those three, all can be accurate if installed, calibrated and used right. All three have their drawbacks.
But Lawler ask about GPS vs mechanical. He sited a "friend" who claimed such-and-such on mechanical, though his GPS show 6 mph less. Then he wondered what was accurate. I suggested why the difference.
BBT, you later stated: "my boat has a speedometer and one of those pitot thingys in it, but it has never worked since I've owned the boat (4 years) and I have never had any desire to fix it."
Maybe you should fix it.
"It doesn't matter who's going faster, what matters is who gets there first"
Sure, but with jets, he who goes faster also gets there first. More thrust = more acceleration = get there first. On plane acceleration's short lived believe me. In fact, that may apply to more than just jets?
jer

[LVjetboy]

Her454, hope for me? I'm not waiting.
jer

[steelcomp]

I've been reading this post, and the conclusion I come to is at best, speedos aren't reliable. I have a Nordskog "competition" 120 mph speedo that is my only ref to speed, since I haven't borrowed or bought a GPS. I rely on it to indicate changes, and hope that it's fairly accurate, but I also know that it's probably not.
My point, if GPS matches Vette speedo, matches boat VDO Speedo, matches Magellon Speedo, then maybe accurate?? That's my experience tho boaring to some such as yourself. And maybe an answer to Lawler's original post? Not that all mfg speedos are accurate as there can be a calibration error. Not that all GPS's are accurate as there can be update and signal strength error.
Hey Jer, way to go...you did it again. :yuk: Instead of keeping things to the topic, you managed to turn another useful post into one of your personal pissing partys. :argue: FYI...you sort of make a valid point, but then you cancel it in your own post. The only thing you really offered to anyone is that YOUR speedo happens to be accurate, but then you state correctly, that not all mfgs speedos are accurate. DUH!! So really, all you told us was ??? that was useful? You get into these "absolutes" and argue symantics that no one really cares about. Everything is relative, and there's nothing new under the sun!!!
Nothing is "perfectly" accurate, and I would venture a guess that everyone here is intelligent enough to understand that. :cool: The question, I think, is which is most reliable? One thing you forgot to mention in all your wisdom and analysis, is that a pitot dosent take into consideration any kind of current, so if you're in a river or any other kind of moving body of water, you can throw your pitot numbers out the window unless you know exactly what the speed of the current is.
Easae up, Jer. There's nothing personal on these boards, until you make them so. Or maybe that's exactly what you intend. :confused:

[steelcomp]

Either that Bud or we can run?
:D :D
jer
Jer,
We've been trying to get you to bring that scow of yours to Ming...there's plenty of guys who would LOVE to run you (including me). Recorded, relatively (by your standards) accurate, irrefutable results. In front of a crowd, God, and everyone. You could be king of the hill... :D
...or just disappear into the crowd of obscurity and mediocrity! :sleeping:

[Squirtin Thunder]

LVjetboy,
Jer,
I want to hear your sterio while running down the track.
Jim

[Lawler]

....well I never expected this thread to get into all of this.....but anyway. The only thing I was curious about was to see if anyone has experienced anything as far as a regular difference between the two types of gauges. I know I spent a decent penny on my Auto Meter GPS gauge but I think it was money well spent. I feel that it's acurate and now I can fine tune my motor using the GPS and the RPM gauge..almost like using a dyno if you know what I mean. I have just heard a few things about mechanical gauges that I didn't like and I was lokking for accuracy/consistancy.

[Squirtin Thunder]

I have used GPS and a pito tube Speedo, I am not going to say that all speedos are accurate but I will say that it is another tool to help diagnos problems and help in tuning. It seems that a lot of guys out there think they have 113mph jet boats. When it all comes down who really cares. When a kid comes up to you at the gas station and asks how fast it is it is not that he really wants to know he just thinks its cool and wants you to talk to him. Which makes him feel good, because he thinks your cool. I have heard fathers talking to there kids as they walk up to the boat saying, Look son thats a Raceboat !!! And I proudly say no it is a family ski boat. Well how fast is it, it must do at least 100mph !!! I say no it is right at 74mph, then the no way your kidding me right??? thats for the insurance guys right ??? No sir thats how fast it really is. Yes I have a goal of 90mph but that is just one of my goals in life. It is just something to strive for. Some say that I will never see it and I just say we will see. Anything is possible. Desk top dyno and JPC give you some possible numbers, again just numbers. You may have a 790hp engine at 6800rpm on a real dyno but as Jer(LVjetboy) has said many times dyno and lake HP are two different things. Controled by boat set up, impeller and hydrodynamic load and airo dynamic load. All of these are not couculated by Desktop Dyno or a real engine dyno, to my understanding.
I really have no idea what I am trying to say but who really care excet in the 5mph no wake doze. I have not seen anyother speed limit signs on the water yet !!!
Well 28mph-36mph on a slolom course, but hell we don't use these boats for that anymore.
Jim

[berk]

I didn't read your post because your crap usually goes way over my head with all the charts and numbers and crap. Just say it like it is, direct and to the point and maybe I'd understand what in the hell you're trying to say better. In as much as I didn't read your post, I didn't dismiss it as anything. Maybe I'll read it and see if I can make heads or tails of it.
Hey Jer, way to go...you did it again. :yuk: Instead of keeping things to the topic, you managed to turn another useful post into one of your personal pissing partys. :argue: FYI...you sort of make a valid point, but then you cancel it in your own post. The only thing you really offered to anyone is that YOUR speedo happens to be accurate, but then you state correctly, that not all mfgs speedos are accurate. DUH!! So really, all you told us was ??? that was useful? You get into these "absolutes" and argue symantics that no one really cares about. Everything is relative, and there's nothing new under the sun!!!
Easae up, Jer. There's nothing personal on these boards, until you make them so. Or maybe that's exactly what you intend. :confused:
THANK YOU

[LVjetboy]

Berk you're full of shit as usual. Lawler, Squirtin and Steel comp all make valid points...you just quote then ride on others posts. Have you no real thoughts in you head? I'll explain later...
jer

[Mr.&Mrs.Budlight]

I got it guys! Call the Bureau of Reclaimation & get output from dam, mulitply depth of river X the width of river in yards,divided into cubic acre feet released from dam, subtract number of cans of Budlight left in cooler. make another pass and float back from dam while using my laptop wireless connection to access Mapquest to satelite in space, to triangulate GPS for last speed pass. Fire up blender & make a drink while listening to thumper stereo[LV Jetboy]. Then go to bar and brag about how fast my boat is while consumming more Budlight. :D :D

[Squirtin Thunder]

Budlight,
"Thats it in a nut shell", but you have to call them right before you run, not 4hrs before, but then again it takes that long to get all the info right????
LVjetboy !!!!!
Jer,
I want to here your stereo going down the track, Now that would make it a real RiverRacer, and you would make the class of the field.
Jim

[steelcomp]

Now that's what I call proper calibration!!! :D :D :cool:

[Her454]

Her454, hope for me? I'm not waiting.
jer
I should have known. Thanks for helping me prove my point. :rolleyes:

[CrazyHippy]

Not a jet boat, but still valid info.
My mechanical speedo is within 1mph of my Handheld GPS from 45-105ish.
In really calm water it stays acurate too 110, with just a little bit of chop, mid 90's.
from 105ish through120ish, gps reads 2-3 mph higher than the speedo, and above 120, the speedo reads WAY low. I assume it is because the boat is a tunnel, and the speedo pick up is coming out of the water, or possibly cavitating.
Below 45 mph, the speedo reads roughly 5mph high... dont know why.
BJH :cool:

[LVjetboy]

"only reason I ask is that a friend of mine claimed his boat went 70 MPH for the longest time. Well we finally got a chance to run the boat with a hand held GPS and he only hit 64 tops on a calm day although his speedometer said he was doing 70."
Like I said, there's "claims" then reality. I've experienced both. Are you sure his speedo said 70? Sure he said that, but what did it truly read? Pitot often get's the blame for bragin' rights and egos, right or wrong. GPS or radar the great humbler...why's that? Because the pitot's wrong or the person reading it has a bias?
Steelcomp posted: "One thing you forgot to mention jer in all your wisdom and analysis, is that a pitot dosent take into consideration any kind of current, so if you're in a river or any other kind of moving body of water, you can throw your pitot numbers out the window unless you know exactly what the speed of the current is."
Actually, no. Pitot accounts for river current unlike GPS. In other words, pitot measures over-water speed regardless of current speed...directly correlated to jet boat performance gain or loss, unlike GPS. An accurately calibrated pitot will display truer performance than GPS or radar with river current.
Pitot is a more accurate and repeatable measure of performance gain or loss, especially in a river current situtation compared to a lake. Both GPS (and radar) by comparison, depend on upstream or downstream river current. So if you use GPS or radar alone, measuring your latest speed performance upgrade may depend on whether your gps (or excuse me radar) is shot upstream or downstream. And what the river current speed is at that time??
Sorry for the analysis part, not sure about the wisdom part...
But did you not know that?
jer

[Squirtin Thunder]

THEY ARE JUST TOOLS !!!!
and bragging rights too

[LVjetboy]

THEY ARE JUST TOOLS !!!!
Yes they are. Not insignificant as most tools, but often misunderstood and wrongly used or interpreted. As I said...
"Pitot accounts for river current unlike GPS. In other words, pitot measures over-water speed regardless of current speed...directly correlated to jet boat performance gain or loss, unlike GPS. An accurately calibrated pitot will display truer performance than GPS or radar with river current."
Does everyone use and interprete GPS or Radar accurately in the same context as pitot??
jer

[Squirtin Thunder]

LVjetboy,
I will have to get a new speedo soon it only goes to 75mph and will push to 85mph, no numbers but unmarked to stop. I love all my TOOLS!!!! My wife does tooo !!!!
Jim

[LVjetboy]

New speedo? Go for 100+ As most wifes or g/fs would admit, tools only enhance the experience, tho few admit. No matter the top speed. I say, go for the gold.
jer

[Squirtin Thunder]

LVjetboy,
Do you have a link to that speedo from VDO, thats what I am using now and it is acually real close 1mph-3mph sometimes slower sometimes faster but a good average. Hell most people think that there torque wrench is accurate because its new. Hell have you ever checked one those Flippin thing are so far off it sick. I ave one of the electronic ones that I put on my torque wrench and I have seen 10lb-22lb on my good snappon . I have sent it to Craftsman three time in the last 5 years to get recalibrated. It does make a difference on that.
Jim

[LVjetboy]

I could find a link to my vdo if anyone cares. My point was, mechanical or GPS or radar can be accurate or not. Depends on the user, GPS or gage and the user's understanding and accuracy of reporting true measurements.
Yes, like you, I've had my torque wrench checked for accuracy. It was right on. I've also compared it to other wrenches...again very close. Not that torque wrench calibration is the end-all in proof of speed measurement accuracy. Just that GPS and pitot speed are not and will never be the same speed thing...for obvious reasons. Even if both are a perfect match to reality...
jer

[Squirtin Thunder]

Jer,
I am serious on the speedo thing. My torque wrench get out of tune because I use it a lot. Believe it or not my old needle torque wrench is alway very close. I have been using VDO gaudges for years and they always seem to be closer than some others.
Jim

[kojac]

....well I never expected this thread to get into all of this.....but anyway. The only thing I was curious about was to see if anyone has experienced anything as far as a regular difference between the two types of gauges. I know I spent a decent penny on my Auto Meter GPS gauge but I think it was money well spent. I feel that it's acurate and now I can fine tune my motor using the GPS and the RPM gauge..almost like using a dyno if you know what I mean. I have just heard a few things about mechanical gauges that I didn't like and I was lokking for accuracy/consistancy.
Lawler,
When you make changes to your combination (rideplate, shoe, wedges, wear rings,impellars, or engine combintions, etc) have you observed whether your GPS has given concrete changes up or down in top speed? So far I have only used the decatuar radar gun to find which combinations work best in the quarter mile.
A bad experience with the pitot pickup being yanked out of the stern of the jet caused a hole in the boat. I don't use the speedometer anymore.
Problem as stated previously with the radar is only me and a few others are
foolish enough to sit and wait for a boat to come straight at them at 118 + miles an hour to get what we hope is an accurate reading.
I have had more than one boat start to hop and skid and slide uncontrollably
while coming at me and would like to be able to rely on a safer solution for getting information to the changes I make in my combo.
Course this don't help me much when I radar others.
Kojac

[Lawler]

I haven't made a ton of changes to the jet yet but the changes I have made have shown and made a difference on the GPS. I personally have found it to be very responsive and consistant with changes. Here's the style I went with. They match real nice with my boat.
http://shopping.rexmar.com/Merchant2/merchant.mvc?Screen=PROD&Product_Code=AUT200837-40&Category_Code=ProCompMarineCFSpeed

[kojac]

I haven't made a ton of changes to the jet yet but the changes I have made have shown and made a difference on the GPS. I personally have found it to be very responsive and consistant with changes. Here's the style I went with. They match real nice with my boat.
http://shopping.rexmar.com/Merchant2/merchant.mvc?Screen=PROD&Product_Code=AUT200837-40&Category_Code=ProCompMarineCFSpeed
Thanks,
I think I would prefer a digital readout in smaller increments of one mile per hour like on the radar gun. The changes I make on the boats may not show up in increments of five miles per hour.
Some of the changes to the boats only show up or down in 1/2 or one mile and hour on the gun. If the milage changes were not decernable I might tend to disregard them and not use the changes if they proved to be a little awkward or bulky.
But, The GPS could still be an added asset if used in conjuction with the radar especially if and when you reached the increased 5 mile an hour marks.
Also during times radar was not availible.
So one is on order.
Kojac

[Squirtin Thunder]

Why is it the presure speedos have a short sweep compaired to the GPS ones?
Jim

[steelcomp]

Actually, no. Pitot accounts for river current unlike GPS. In other words, pitot measures over-water speed regardless of current speed...directly correlated to jet boat performance gain or loss, unlike GPS. An accurately calibrated pitot will display truer performance than GPS or radar with river current.
Jer, This is one of those cases where it's right, but it's not. What I was referring to when I said the pitot didn't account for current was in the area of "real" speed or 'observable' speed. What you say is true as far as "relative water speed", but it does not take into consideration actual speed (ground speed, if you will). It reads in mph. Add or subtract the speed of the current, and the mph is wrong, from point a to point b. . It's the same with flying. Relative air speed, true air speed, and ground speed. Ground speed is the one that counts, since it's all about getting from point a to point b. But you're right...a pitot is really the only accurate measure of a boat's performance in a moving body of water, unless you have accurate corrections for your electronics, and since the river is completely dynamic, there's no way you could really accurately compenssate for that. The pitot is infinately intelligent when it comes to that.
Good post!

[berk]

you mean the gps is infinately intelligent, right?

[Mr.&Mrs.Budlight]

Does GPS mean gas pedal speed? :confused: :confused:

[Mr.&Mrs.Budlight]

Hey dragboats, Do you have another boat? A black&purple
baker jetboat. Budlight :devil: :devil:

[Squirtin Thunder]

LVjetboy,
Jer, Steel comp ran 92mph@5500 with a MPD "B" impeller. What does this equate to in HP ???
Jim

[REGISTERED USER]

Staying on topic here, even though a few days late, in all this discussion (???), nothing was ever mentioned about the differences in pitiots themselves. From the cheap nylon ones supplied with the Teleflex speedo to the expensive stainless ones supplied by Eddie, Rex and others, how about some input on differences in accuracy?
The one that came with my T-flex speedo when first installed worked well and the system was acurate within about 1 mph from 20-60. Now after a few years the pitiot kicks back about 15 degrees from its normal angle after use, and the readings are off and flutter like hell above 40.
Are all the different pitiots the same or are they matched to the speedo. Common sense says the pressure wouldn't change if the opening sizes were different, but I've been wrong before.

[steelcomp]

you mean the gps is infinately intelligent, right?
Berk...no, the gps reads in increments of measurement translated from digital information. No matter how close the increments, there's always an area of "no information' between increments. A speedo reads a constant (infinite) pressure that moves a needle through a mechanism, and no matter how slight the change, it will register, wheather perceptable or not. Does that make sense?

[steelcomp]

Staying on topic here, even though a few days late, in all this discussion (???), nothing was ever mentioned about the differences in pitiots themselves. From the cheap nylon ones supplied with the Teleflex speedo to the expensive stainless ones supplied by Eddie, Rex and others, how about some input on differences in accuracy?
The one that came with my T-flex speedo when first installed worked well and the system was acurate within about 1 mph from 20-60. Now after a few years the pitiot kicks back about 15 degrees from its normal angle after use, and the readings are off and flutter like hell above 40.
Are all the different pitiots the same or are they matched to the speedo. Common sense says the pressure wouldn't change if the opening sizes were different, but I've been wrong before.
As long as the opening remains perpendicular to the water, the opening size sholdn't matter. Pressure is even and equal in all directions, and water will not compress.

[REGISTERED USER]

As long as the opening remains perpendicular to the water, the opening size sholdn't matter. Pressure is even and equal in all directions, and water will not compress.
That's what I was thinking about the opening size. As far as water being not compressable, what about the air trapped in the tube. Since there is no way to bleed the air out in any system I have ever seen, how does the trapped air affect the readings?
Thinking that even when the air compresses, that the pressure remains equal in all parts of the syatem. Am I on the right track?

[steelcomp]

yup

[Squirtin Thunder]

Steelcomp,
forgot to ask what did the speedo say as you were running down the course???
Were is your crew sir????
Jim
Ron (Jeanyus, Zevron) sorry for using a (32oz) hammer on your boat.

[steelcomp]

Steelcomp,
forgot to ask what did the speedo say as you were running down the course???
Were is your crew sir????
Jim
Ron (Jeanyus, Zevron) sorry for using a (32oz) hammer on your boat.
It said, "faster, faster, faster!!!

[Squirtin Thunder]

Steelcomp,
I am so sorry for not catching the throttle linkage. It is pissing me off that I missed it or didn't check it.
Jim

[steelcomp]

Steelcomp,
I am so sorry for not catching the throttle linkage. It is pissing me off that I missed it or didn't check it.
Jim
No worries...I have no one to blame but myself for that one. Thanks again for the help. :cool:

[Jeanyus]

Steelcomp,
forgot to ask what did the speedo say as you were running down the course???
Were is your crew sir????
Jim
Ron (Jeanyus, Zevron) sorry for using a (32oz) hammer on your boat.
Don't worry about it, you saved me, and I got my best run of the day, hammer boy.

[Squirtin Thunder]

Jeanyus,
Now you have called me a oaky, hammerboy, redneck, and Ford boy. I can live with the last one because I am.
Jim

[LVjetboy]

"But you're right...a pitot is really the only accurate measure of a boat's performance in a moving body of water"
The problem with gps and radar on the river is current. Does the river runner understand and compensate for current, midstream or near shore, same run location as in narrow or wide river, early morning, noon or afternoon flow, each month, year by year? How would you measure and compensate for current??
On the lake no big deal with current. At least radar and gps means no reader parallax or squinting-at-the-needle-and-wishing error. Digits display, accruate or not, like them or not...
jer