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Alright, what do you have to do..........

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Old 12-02-2005, 11:56 AM
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and then you go to the Detroit River with a 7 mph current, you do not have a 75mph boat because your GPS said so on that particular day?
Good question. Then, how fast was it on that particular day?

And, if you always boat on the detroit river, and so do your friends, how fast is your boat if it reads 75mph on your way to the bar?
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Old 12-02-2005, 12:09 PM
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Default Re: Alright, what do you have to do..........

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Originally Posted by Wobble
I have found the best way is to stick the GPS on the dash of my truck, record a speed and then take it back to the boat. Take a picture of the recall and post it here
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Old 12-02-2005, 01:04 PM
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Default Re: Alright, what do you have to do..........

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Originally Posted by Emaginashun
Good question. Then, how fast was it on that particular day?
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Quote:
Originally Posted by Emaginashun
And, if you always boat on the detroit river, and so do your friends, how fast is your boat if it reads 75mph on your way to the bar?
79.5

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Old 12-02-2005, 01:45 PM
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Default Re: Alright, what do you have to do..........

This might expain how the donz jr. got a straight bottom top gun to go 108? NK
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Old 12-02-2005, 01:45 PM
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Question Re: Alright, what do you have to do..........


I guess perception is reality.

Last edited by Emaginashun; 12-02-2005 at 01:48 PM.
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Old 12-02-2005, 02:19 PM
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Default Re: Alright, what do you have to do..........

I drag raced boats for the past 20 years before going "offshore" style boats.
In the early years, our timing systems consisted of 2 cops with radar guns on a pontoon boat beyond the course, in the shutdown zone. Pretty crude stuff. Some boats, particularly those with large inboards did give a decent radar target and reflection. Some, particulary streamlined boats, like a STV or Mirage outboard did not. We ended up putting metal duct tape on some of these boats to get a "reasonable" reading.
Radar can be accurate, but it requires a highly reflective target. There is also an issue with cosine error if not shot directly (0o) at the boat.
Later, and much better, most sanctioning bodies put into use automotive timing equipment like Chrondek systems. These are very accurate and give RTs, ETs, and top speed measured over the final 100 feet of a 1/4 mile course, just like car drags.
Like any electronic device, these weren't perfect, and did occaisionally give some bogus #s, but by and large were very accurate. I'm sure that's why UIM uses a similar system for the official kilo records.
I began using 12 channel handheld GPS about 10 years ago in my race boats to test. The earlier 4 channel units updated so slow, particularly on a drag boat, they were useless. The 12 channel units were usually within a few tenths MPHs of the Chrondeks that we used. The GPS was usually slightly slower, which could have been calibration of the Chrondek system, or
even with the 12 channel units, a slightly slower update.
GPS can be fooled by flowing bodies of water, since they are measuring SOG/speed over ground. Other than that, I have found the 12 channel units very accurate.
Regards,
Steve

Last edited by Steve Zuckerman; 12-02-2005 at 02:25 PM.
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Old 12-02-2005, 02:44 PM
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Default Re: Alright, what do you have to do..........

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GPS can be fooled by flowing bodies of water, since they are measuring SOG/speed over ground
Question; how can the GPS determine the difference between water and land?

It is simply measuring distance traveled with a combination of movement per unit time and computing the doppler shift in the pseudo range signals from the satellites.

The speed is smoothed and not instantaneous speed.
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Old 12-02-2005, 03:33 PM
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Default Re: Alright, what do you have to do..........

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Originally Posted by Emaginashun
Question; how can the GPS determine the difference between water and land?
It can't; therein lies the problem.
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Old 12-02-2005, 03:51 PM
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Default Re: Alright, what do you have to do..........

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Originally Posted by birdog
In 10 footers !!
So the rule is 1 MPH per beer, and 1 foot per shot. NOW I get it


Last week was my birthday, and I swear I was doing 140 in 15 footers

For a real world GPS speed, just backup the run going the other direction and average it like the big boys do in the kilo runs. I'm always up for 1 more high speed run.....that's a perfect excuse for the girlfriend.....
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Old 12-02-2005, 04:09 PM
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Default Re: Alright, what do you have to do..........

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Originally Posted by CigDaze
It can't; therein lies the problem.
Horizontal speed remains constant and surface conditions do not factor in on GPS measurement.

Last edited by Emaginashun; 12-02-2005 at 04:17 PM.
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