Speedometer 4MPH Off According To GPS

[dtescher]

Mt speedometer is off by 4mph according to my GPS. Is there a way to test speedometer? It's original to the boat. 1997 Reinell 4.3GL PLKD #4110144649

 

[matt167]

Re: Speedometer 4MPH Off According To GPS

4 MPH is nothing. Supprised it's not reading 10 MPH or more off. Normal boat speedometers are not accurate and that is why the market is switching to GPS speedometers. The speedo you have is basically an air speed gauge that measures air pressure. The water pushes against the air in the tube and makes it work, but they are never 100% accurate

 

[Don S]

Re: Speedometer 4MPH Off According To GPS

The speedometer for your boat has nothing to do with your engine or drive. It's just a pressure pitot tube mounted on the transom. Very inaccurate.

 

[Nickypoo]

Re: Speedometer 4MPH Off According To GPS

Yes conventional boat speedometers measure stagnation pressure at the tip of a pitot. This isn't a very precise way to measure speed but it's simple and reliable.

GPS speedometers are more accurate, but only on land. What you are seeing on the GPS is your speed relative to land. You could be in a current where your water speed is different than the land speed. In this case the pitot may be more accurate.

 

[Don S]

Re: Speedometer 4MPH Off According To GPS

You could be anchored in a 10 mph current with the engine off, and the speedometer on your boat would show 10 mph. But you are anchored and going nowhere. The GPS gives you speed over the ground, the speedometer gives you speed the water is passing the pitot tube.

 

[dtescher]

Re: Speedometer 4MPH Off According To GPS

Good enough. I won't worry about the difference then. Thanks for the info.

 

[82rude]

Re: Speedometer 4MPH Off According To GPS

another name for them is lie o meter.

 

[rallyart]

Re: Speedometer 4MPH Off According To GPS

I thought the Lie-O-Meter was the fuel gauge.

 

[roscoe]

Re: Speedometer 4MPH Off According To GPS

I thought the Lie-O-Meter was the fuel gauge.

No, thats the "Do you feel lucky" meter.

 

[rallyart]

Re: Speedometer 4MPH Off According To GPS

Oh well, at least I know that Port means a red wine.

 

[etracer68]

Re: Speedometer 4MPH Off According To GPS

And not to be confussed with, RED, "RIGHT", RETURN.

 

[cuenta]

Re: Speedometer 4MPH Off According To GPS

My brother made ​​a bigger hole to pilot tube connection
to trick the speedometer
he gain 10 MPH
jajajajaja..

 

[tpenfield]

Re: Speedometer 4MPH Off According To GPS

FWIW - I have found that the pressure speedometers are most accurate in the mid speed range, like 30 - 40 mph.

it under states at lower speeds and over states at higher speeds versus the GPS. I often see wild claims of top speed for boats in Ad listings. . . I'm thinking they got those from the pressure speedo and not the GPS

 

[Campylobacter]

Re: Speedometer 4MPH Off According To GPS

I often see wild claims of top speed for boats in Ad listings. . . I'm thinking they got those from the pressure speedo and not the GPS

You are a far more charitable than I am, I assume they are lying. Or that all the 3.0's around here can do 50.

 

[coolbri70]

Re: Speedometer 4MPH Off According To GPS

when i'm checking my top speed with gps i like to run upriver then down, i figure the diffirence is the rivers current speed and my top speed in the middle, so even if your speedo is correct, it will be off from your gps speed if the water is moving too

 

[Capt Ken]

Re: Speedometer 4MPH Off According To GPS

I'm surprised the difference between running in hard water and soft water hasn't been discussed. We all know the boats run slower in hard water due to more hull resistance. Extensive studies in prop wash samples has proven this theory.

 

[dan02gt]

Re: Speedometer 4MPH Off According To GPS

FWIW - I have found that the pressure speedometers are most accurate in the mid speed range, like 30 - 40 mph.

it under states at lower speeds and over states at higher speeds versus the GPS. I often see wild claims of top speed for boats in Ad listings. . . I'm thinking they got those from the pressure speedo and not the GPS

That's exactly how mine is. It's within 1MPH of my GPS between 30-50, but by the time I get to the high 50s it's as much as 5 off.

I like to say the that the GPS slowed a lot of boats down.

 

[agallant80]

Re: Speedometer 4MPH Off According To GPS

Remember your GPS is going to show speed over ground, the meter in your boat will show speed over water, if there is a current it will add to your speed or take away depending on direction.

 

[phonfish]

Re: Speedometer 4MPH Off According To GPS

Make sure you are not reading mph on one and knots on the other.

 

[emilsr]

Re: Speedometer 4MPH Off According To GPS

Check your boat's speed on radar and you may find the GPS speed to actually be higher.

My first 2 boats didn't even have a speedo. Now I know why.