Trip meter reading double?

[Capt. Jack Sparrow]

We've got a TZT14 (dual displays) getting GPS from a GP-330B. The vessel also has a FI-70 display. When re-setting both the TZT14 and the FI-70 trips to zero, we find that the TZT14 distance is double that of the trip reading on the FI-70. All sets are set to NM ad using same GP-330B for GPS/trip info. We did a short trip and FI-70 reads 7nm and TZT14 reads 13.29nm. The trip was about 7nm so we're assuming that the FI-70 is showing correct reading?

 

[Johnny Electron]

The TZT14 and FI-70 will never exactly read the distance the same way as they use different methods of calculating the travel. The FI-70 will use STW or SOG while the TZT14 will calculate based on your Lat/Lon movements. While they won't perfectly match, they shouldn't be so far off from each other. I expect that your GPS must have lost position at some point after you started the trip meter and it jumped GPS location or something that contributed to a lot of extra mileage. You might want to check your Position, COG/SOG, and Date and Time sources in the DATA SOURCE selection to ensure you have your best position source selected and monitor what might be happening with your GPS data.

 

[Capt. Jack Sparrow]

The TZT14 and FI-70 will never exactly read the distance the same way as they use different methods of calculating the travel. The FI-70 will use STW or SOG while the TZT14 will calculate based on your Lat/Lon movements. While they won't perfectly match, they shouldn't be so far off from each other. I expect that your GPS must have lost position at some point after you started the trip meter and it jumped GPS location or something that contributed to a lot of extra mileage. You might want to check your Position, COG/SOG, and Date and Time sources in the DATA SOURCE selection to ensure you have your best position source selected and monitor what might be happening with your GPS data.

Thanks for the reply. I'm sure we checked that the DATA SOURCE on both the TZT14's (there's two) and the FI-70 was set to GP-330B as there is no other GPS or speed source on the vessel (unless something coming from AIS model FA-30).

Regardless of the distance travelled, the Captain reported that he was consistently getting "double" the distance reading (NM) on the TZT14 as to what he was getting on the FI-70. We believe that the TZT14 is correct, given the distance travelled. To ascertain the problem, we reset the trips on all units, checked data source and we did a trip of approx. 14nm. The results were as per the attached photo.

Funnily enough the vessel next door to us has a GP-1971F and a TZT2, both get GPS from SCX-20. The TRIP meters are also a few NM different after each trip

It seems crazy that different plotters / GPS sources used different methods to calculate TRIP meter distances.

PS, it would allso be a great idea for Furuno to include at least two decimal points in the TRIP meters of the FI-70 and GP-1971F data screens, like they have on the TZT plotter data boxes.

 

[Johnny Electron]

Yes, we are aware they calculate differently and it can be confusing being they are from the same company. We made this point with the parent company and they plan to start standardizing the ways of calculating. It stems from FI70 being more designed for the sailboat market and the TZT being made for the power boat market. TZT14 hasn't had new software in awhile and unlikely to go beyond v6.03 but I recommend you check that you are running that newest version. Based on GPS, unless GPS is lost or the unit is placed in DEMO the TZT14 would be correct. FI70 because STW can override SOG in the calculations can be a bit more problematic because water paddle wheels tend to faul easier.