Unusual GPS speed display today...

M

matt_unique

New member
Well it's Spring launch time and this is when we will be chatting about unusual readings!

I was running Napoleon up to speed today and I happened to notice whenever I went above about 35 knots my GPS speed reading would blink to 0 knots, then it would show the actual speed (i.e. 40 knots), then blink to 0 knots, etc. It did this over and over again whenever I was about 35 knots.

Below 35 knots the speed reading was steady, no blinking or anything out of the ordinary. I have a 1 year old Furuno 1834 C/NT with the BBWGPS GPS receiver. My kneed jerk reaction is a loose wire or something but it was no less "bumpy" at 30 knots as it was at 35 knots. I fired off an email to Furuno technical support but I wanted to bounce it off you guys here.

I was following a route based on GPS waypoints I had previously entered. I did not appear to loose my position or chart display it was just the speed reading.

By the way, I topped out at 41.5 knots on the GPS today. Not bad considering I was fully fueled (900 lbs of gas).

Thanks
 
Do you have a paddlewheel-style through the water speedometer and how well does it synch with your (calculated) GPS-based speedo?

Paul Priest
Sequim
J.C.Lately
 
I only have GPS speed. The speeds today matched the speeds that I recorded last season with the same RPM.

I mentioned I was thinking a loose wire but if that were the case it should show erratic readings at 30 knots as it does above 35. It does not make sense that it only happens above 35 knots. In fact, I bounced over some larger waves at the end of my trip today cruising at 22 knots and there were no erratic readings.

It will be interesting to determine the cause/solution....thanks for brainstorming.
 
Let's see. A GPS doesn't measure speed directly, but computes position, differencing successive positions and divides by thyme. Remember dead reckoning? Average speed = change in position/thyme.

Anyway, I assume that for speeds over 35 knts, there is something in the computational algorithm that burps. Or the processor runs out of time to compute the speed in one display cycle. If you can, try it in your car.

Boris
 
Ha ha - well the only way I could try it on the road would be under tow. I need a volunteer to ride in Napoleon and take readings while we cruise down the highway ;)

Mine is a fixed unit with external antenna. Taking a look at the owners manual I see there is something called a "speed/course smoothing" adjustment for the GPS...I'm throwing pasta at the ceiling until I hear from Furuno at this point...maybe it's an adjustment issue. I can also run a GPS system test.

I will figure it out eventually and the ideas are helpful!
 
Pat Anderson":1glb6cm1 said:
Boris - have you ever tried DR with parsley, sage or rosemary instead of thyme? :lol:


journey on":1glb6cm1 said:
Remember dead reckoning? Average speed = change in position/thyme.



Boris
Click to expand...
Click to expand...

Ooh, ooh - I know this one... "Summer Breeze" by Seals and Crofts. Oops, wrong thread. :wink:
 
Jim might know his FD dolphins, but he don't know his Simon and Garfunkle.

Once in a while my Garmin will go screwy on the speed and I turn it off and back on to get it to work. Must have some Windows software in it. The Furuno guys will help you out, I'm sure. They seem to be the best for support.
 
TyBoo":3b2ozwnf said:
Jim might know his FD dolphins, but he don't know his Simon and Garfunkle.

Once in a while my Garmin will go screwy on the speed and I turn it off and back on to get it to work. Must have some Windows software in it. The Furuno guys will help you out, I'm sure. They seem to be the best for support.
Click to expand...

Thanks for the gentle nudge to get the thread back on track :)

Furuno support has been excellent. I'm sure I will hear from them quickly next week.
 
Come on, Pat, you're pulling my leg. Everyone knows that:

Max speed = Avg speed* parsley

Change in elevation = height / rosemary

Depth = fathoms ^ sage

Thyme is the correct unit to use.

Boris
 
Pat Anderson":l6gpwdz2 said:
I feel another thread hijacking coming on!

Nope, "Scarborough Fair" by Simon and Garfunkle.


JamesTXSD":l6gpwdz2 said:
Ooh, ooh - I know this one... "Summer Breeze" by Seals and Crofts. Oops, wrong thread. :wink:
Click to expand...
Click to expand...

:mrgreen: :mrgreen: :mrgreen:

OK, then, was it the Guess Who who did "No Thyme Left for You"? Or who is green, wiggles, and sings? Elvis Parsley. Or... um, nevermind. :oops:
 
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