speedometer vs. GPS

[Happy Gourmand]

Originally Posted by chipj29

So what would happen if you were going 55 (which you thought was 45 due to your faulty speedo) and you got a ticket. How can you know your actual speed if your speedometer is that far off? I know one thing...I would be taking that one to court to let the judge decide. As far as I know, GPS is not required equipment...

Probably the same thing that would happen if you were actually doing 76 on Rte 93, but you THOUGHT you were doing 65. It is your responsibility to know how fast you are travelling. I doubt you would find a sympathetic judge.

[ossipeeboater]

keeping stock pitot is the key, on my old speedboat the oringinal pitot was within 2 mph of the GPS, the bracket broke and the new one that replaces it was off by 5-7 mph, not sure if the pcikup was longer on the old one or shorter. On my toon it's off by a consistent 5 mph at just about all speeds.

[brk-lnt]

Originally Posted by The Phantom Gourmand

Probably the same thing that would happen if you were actually doing 76 on Rte 93, but you THOUGHT you were doing 65. It is your responsibility to know how fast you are travelling. I doubt you would find a sympathetic judge.

I somewhat disagree. Measuring speed accurately in a vehicle is much easier than on a boat, and speed limits have been a much more predominant item in automobile law vs. boating law.

It should be fairly clear by now that the reality is you're not likely to find yourself in this scenario. You would pretty much have to be traveling near the speed of light before you are going to get a speed limit ticket.

[Slickcraft]

My Garmin GPS steady state speed accuracy is 0.05 meters/sec or 0.1 mph. Position data is updated once per second. I might accept the GPS reading over the speedo.

While there are position errors in GPS, those errors change slow relative to the once per second update rate so distance traveled in one second is very accurate.

[Kamper]

I have bought 2 "paddle-wheel" speedometers for 2 different boats. The packages included directions on how to accurise them. Basically you needed a measured distance so you could "clock" the boat and adjust the gear accordingly. There is probably a similiar requirement for "pitot tube" versions.

I doubt most factory boats have this procedure performed on them. Speed precision apparently was not considerred that critical since speedo/GPS discrepancy is occasionally discussed on other boat forums I visit.

If you want to accurise your instrument it is simpler to use a GPS than a measured course. During a calm period (no wind or chop) operate your boat at various speeds on a lake or large pond. Compare the readings. Adjust your speedo according to the directions. Repeat the procedure until you are comfortable with the results.

If you don't have, and cannot get, directions for your version examine the back of it for calibration access. Make a note of the current settings if possible. Then expiriment to see what makes it show higher or lower.

If you are not comfortable working on these systems then make a mental note or written table of the discrepancy at various speeds.

That's all I think I know about that.

Good luck!

[BroadHopper]

I was reading an article posted in 'Heloise' the other day. A LEO from Texas says to never use the GPS as a spedometer as it is inaccurate????

He claims to be pulling people over who says: 'Officer, My GPS says I am going the speed limit!' They were traveling over the speed limit. He hinted on Heloise that people should not use their GPS as a speedometer as they are inaccurate.

As stated in this thread I find the boat's speedometer readings off from my GPS reading. I am planning on using GPS to keep within the speed limit on the lake. I have observed my GPS as 'dead on' with the speedometer readings in my truck. I also heard that stored data in GPS is being used as evidence in court cases.

Should I be confused?????

[ishoot308]

Originally Posted by BroadHopper

I was reading an article posted in 'Heloise' the other day. A LEO from Texas says to never use the GPS as a spedometer as it is inaccurate????

He claims to be pulling people over who says: 'Officer, My GPS says I am going the speed limit!' They were traveling over the speed limit. He hinted on Heloise that people should not use their GPS as a speedometer as they are inaccurate.

As stated in this thread I find the boat's speedometer readings off from my GPS reading. I am planning on using GPS to keep within the speed limit on the lake. I have observed my GPS as 'dead on' with the speedometer readings in my truck. I also heard that stored data in GPS is being used as evidence in court cases.

Should I be confused?????

When going in a straight line your GPS is extremely accurate. The problem becomes if you take readings while taking turns. Since your GPS only works on forward momentum, accuracy diminishes while turning. The sharper the turn the less accurate it becomes. I would trust my GPS whlile going straight way more than any speedometer.

As far as GPS being used as evidence in court cases, I have not heard of this, but who knows, in this day and age of "big brother" looking at everything we do I wouldn't doubt it. I have heard of On Star being used in court cases however.

Dan

[OCDACTIVE]

ishoot308, great explaination of the gps speed. I have seen in many situations that in a slight turn it will actually show a greater speed then the true speed. This is why when racers are trying to break speed records they have to complete two passes to ensure accuracy.

My gps speedo needs a new battery, but livorsi wants $200 to do the replacment. However, there is no law that I have to have a speedo on the boat. So frankly I don't know how fast or slow I am going. Would be very hard to make that stick in court.

[VtSteve]

On Saturday, I tested mine out. The speedo is accurate up to around 45 to almost 50, then it goes my way

I will be testing the Garmin against the Tom Tom next weekend. As of now, the best GPS I have in my boat is the iPhone, with a $9.95 Navionics East app in it. I can see everything better, including the marker buoys, than with the Garmin 440. Interestingly, I have the optional $200 card in the Garmin.

[brk-lnt]

Originally Posted by OCDACTIVE

My gps speedo needs a new battery, but livorsi wants $200 to do the replacment. However, there is no law that I have to have a speedo on the boat. So frankly I don't know how fast or slow I am going. Would be very hard to make that stick in court.

$200? Depending on the model, that is like 70-80% of the price when new. You should bring it by, my guess is the battery could be replaced for about $10.

[OCDACTIVE]

Originally Posted by brk-lnt

$200? Depending on the model, that is like 70-80% of the price when new. You should bring it by, my guess is the battery could be replaced for about $10.

I have been online and apparently if you send it back to livorsi they give you a new model for $200 as an exchange. I have been told I can run a line to my new GPS once I get the network up and running which may negate the need to replace the battery or unit at all.

But frankly, I don't care what speed I am at. I am driving safe and prudent. Until there is a law that says I have to have a speedo it really doesn't matter.

[Excalibur]

I put a portable GPS in my boat for a weekend and wrote down the tachometer revolutions for particular speeds.
My pitot tube kicks up over 60 on Lake Winnisquam..

[lawn psycho]

My speedometer sucks. It doesn't even read until about 25 MPH and then when it does, it's off by 10MPH when compared to my GPS.

However, my boat tops out at 48.5MPH according to my GPS, and that's on flat water with only two people. I don't see a ticket in my future anytime soon

[ApS]

Originally Posted by The Phantom Gourmand

Probably the same thing that would happen if you were actually doing 76 on Rte 93, but you THOUGHT you were doing 65. It is your responsibility to know how fast you are travelling. I doubt you would find a sympathetic judge.

The statement ignorance of the law is no excuse is centuries old:

"...Ignorance of the law excuses no man; not that all men know the law; but because 'tis an excuse every man will plead, and no man can tell how to confute him.
—John Selden (1584-1654)...

If a defendant were allowed to escape legal responsibility for his acts, merely by saying "I didn't know it was wrong/illegal", the system of using law to regulate human conduct would collapse. So the doctrine is a practical necessity...This doctrine still has vitality and validity today..."

http://www.rbs2.com/cc.htm

The same source continues:

"...A related concept in law is "wilful blindness": the criminal defendant who should have known, and could have asked, but deliberately chose not to ask. The law regards "wilful blindness" as equivalent to knowledge. U.S. v. Jewell, 532 F.2d 697, 700-701 (9th Cir. 1976), cert. denied, 426 U.S. 951 (1976). Cited with approval in U.S. v. Lara-Velasquez, 919 F.2d. 946, 950-951 (5th Cir. 1990)..."

[chipj29]

Originally Posted by Acres per Second

The statement ignorance of the law is no excuse is centuries old:


http://www.rbs2.com/cc.htm

The same source continues:

Please explain how someone on a boat is supposed to know exactly how fast they are traveling if their boat does not have a speedometer? There is no law that requires a boat be equipped with a speedometer. That would be my challenge to a judge if I were to get a ticket.

I am not being ignorant of the law, as I am perfectly aware that there is a speed limit. Without a speedometer, I might be ignorant of my exact speed however.

[Capt. Quint]

Originally Posted by chipj29

Please explain how someone on a boat is supposed to know exactly how fast they are traveling if their boat does not have a speedometer? There is no law that requires a boat be equipped with a speedometer. That would be my challenge to a judge if I were to get a ticket.

I am not being ignorant of the law, as I am perfectly aware that there is a speed limit. Without a speedometer, I might be ignorant of my exact speed however.

Yeah, I suggest you don't try tellin that to the judge. My pickup doesn't have a speedo or doors for that matter. I got a speedin ticket that night when that college boy Hooper just kinda rolled out'a the truck on the salt pond road, and it didn't do no good when I told judgy I couldn't tell how fast I was going cause I aint got no speedo. No, give up on that excuse mister.

[chipj29]

Originally Posted by Capt. Quint

Yeah, I suggest you don't try tellin that to the judge. My pickup doesn't have a speedo or doors for that matter. I got a speedin ticket that night when that college boy Hooper just kinda rolled out'a the truck on the salt pond road, and it didn't do no good when I told judgy I couldn't tell how fast I was going cause I aint got no speedo. No, give up on that excuse mister.

Absolutely would bring it up to a judge. It is a lot easier to gauge ones speed in a vehicle on a road than in a boat. For one, in a car you can compare your speed to other vehicles. You can judge your speed based on time/distance to fixed objects. In a boat, there are way to many variables to even think about guessing speed.

Are speedometers required equipment in cars?

[Happy Gourmand]

Seems like if you don't have a clue how fast you are going....maybe you shouldn't be behind the helm.
If you want to captain a vessel, you should be ready to accept responsibility for all aspects of the operation of said vessel. Short of that, keep your boat tied up to the dock. That will help make the lake safer for the rest of us.

[OCDACTIVE]

Originally Posted by The Phantom Gourmand

Seems like if you don't have a clue how fast you are going....maybe you shouldn't be behind the helm.
If you want to captain a vessel, you should be ready to accept responsibility for all aspects of the operation of said vessel. Short of that, keep your boat tied up to the dock. That will help make the lake safer for the rest of us.

I have been driving boats my entire life. If you don't have a speedo it is difficult to know exactly what your speed is. If you know your boat you know that based on the RPM level where around your speed is but no one knows exactly without a speedo gps or otherwise.

As an example going at cruising speed on a flat windless day at 3000 rpms feels slow (in my boat at least)

You change that into a strong head wind with 2 - 3 foot chop it feels like warp speed. It is all relative. However, you may actually be going slower.

As long as you are traveling at a safe and prudent speed for the conditions the # is arbitrary.

[Skip]

Of course if enough folks complain that is is wrong to have a speed limit but not require speedometers on boats, some intrepid legislator will listen and file legislation to require speed measurement devices on boats travelling on waters with limits.

And then some of those same folks will complain about "nanny state" and "ridiculous legislation".

And this, my friends, is a perfect example of how we get all these rules and regulations that we are all (most of us anyway, myself included) so fond of complaining about!

[OCDACTIVE]

Originally Posted by Skip

Of course if enough folks complain that is is wrong to have a speed limit but not require speedometers on boats, some intrepid legislator will listen and file legislation to require speed measurement devices on boats travelling on waters with limits.

And then some of those same folks will complain about "nanny state" and "ridiculous legislation".

And this, my friends, is a perfect example of how we get all these rules and regulations that we are all (most of us anyway, myself included) so fond of complaining about!

agreed Skip... However that would be extremely tough to regulate considering boats may not or may not have been manufactored with them. The logistics would be crazy.

[Capt. Quint]

Originally Posted by The Phantom Gourmand

Seems like if you don't have a clue how fast you are going....maybe you shouldn't be behind the helm.
If you want to captain a vessel, you should be ready to accept responsibility for all aspects of the operation of said vessel. Short of that, keep your boat tied up to the dock. That will help make the lake safer for the rest of us.

Aye, Not like going down the pond chasin' bluegills and tommycods...we're talkin' 'bout up around 40 knots or so- or maybe 22 in the wee hours. You certainly know if you're approachin' the max legal speed- 'specially if there's a small 3-4 foot chop on the lake. If you have the urge to go max legal speed and not a prudent one- then get yerself a good working speedo or one o' them new GPS things. Any keep yer eyes open an' not on tha' damn electronics stuff!

[Mee-n-Mac]

Originally Posted by chipj29

Absolutely would bring it up to a judge. It is a lot easier to gauge ones speed in a vehicle on a road than in a boat. For one, in a car you can compare your speed to other vehicles. You can judge your speed based on time/distance to fixed objects. In a boat, there are way to many variables to even think about guessing speed.

Are speedometers required equipment in cars?

Yes speedos are required equipment on cars. One of the times this topic came up I even listed the Fed regulation to that effect. There's also an accuracy requirement, I think it was +/- 2%. In any case you might plead to the judge "I didn't think I was going that fast" and if you were only 5-10 mph over, he might believe you. On the other hand if you doing 80+ mph in a decked out 300K$ gofast with twin supercharged engines ... my guess is he's not going to buy the story.