Airmar DST810 Always Reads Slower Than SOG

[DragonflyBob]

I have a chronic issue with a relatively new (about 6 months old) Airmar DST810 speed and depth transducer consistently reading 1-2 knots slower than the SOG shown on our B&G Triton chartplotter and MFD’s. We sail predominately on Lake Pontchartrain and in the middle areas of the lake where we sail, there is not that much current to cause that kind of difference and the delta we see is always the DST810 lagging behind the SOG. We’ve checked the boat’s electronics SOG against our iPad Navionics app and they nearly always match. We have taken the boat through some inlets and channels that have significant current and seen the delta change accordingly to how the current is flowing against the boat so it appears the unit is responding correctly.

I’ve cleaned the DST810 impeller several times and always make sure the directional arrow is dead nuts parallel to the centerline of the boat. Our boat is a trimaran so never heels more than about 5-10 degrees and we see the issue whether the boat is flat in light air or flying the weather float if the breeze comes up. The sensor is located about 12” off the boat’s centerline.

I do have the CAST app on my phone and admittedly I’ve never tried using its calibration capability so this could be the path to a solution.

Anyone else had this chronic issue or can it be cured through calibration using the CAST app?

Thanks!

[GordMay]

Originally Posted by DragonflyBob

I have a chronic issue with a relatively new (about 6 months old) Airmar DST810 speed and depth transducer consistently reading 1-2 knots slower than the SOG shown on our B&G Triton chartplotter and MFD’s ...
... Anyone else had this chronic issue or can it be cured through calibration using the CAST app?

I'd, certainly, try calibrating the instrument.

[Dr. D]

Your chart plotter (or other instrument) should permit adding a multiplicative term to the readout from the DST810. My Triton2 has that calibration feature. Now, the correction isn't strictly linear, so it is a bit off at low speed and high speed, but closer than what you are seeing.

[DragonflyBob]

Originally Posted by Dr. D

Your chart plotter (or other instrument) should permit adding a multiplicative term to the readout from the DST810. My Triton2 has that calibration feature. Now, the correction isn't strictly linear, so it is a bit off at low speed and high speed, but closer than what you are seeing.

Cool, that’s a feature I will try to use. Thanks for the feedback!

[SailingHarmonie]

SOG is always right, there is no calibration involved. It is as accurate as GPS location.

Paddlewheels are notoriously difficult to keep precise. Not just the wheel itself, but the hull around it needs to be clean for good numbers.

Your MFD manual will have a calibration procedure for it.

[DragonflyBob]

Originally Posted by SailingHarmonie

SOG is always right, there is no calibration involved. It is as accurate as GPS location.

Paddlewheels are notoriously difficult to keep precise. Not just the wheel itself, but the hull around it needs to be clean for good numbers.

Your MFD manual will have a calibration procedure for it.

Understood and agree but it would be nice if we can get a read on boat speed relative to SOG to see if we are being set negatively or positively by current.

[SV Confianza]

You're not alone. Mine showed 1-2 knots slow right out of the box into the boat. I've just been too lazy to calibrate it on my chart plotter.

[Fuss]

I’m sure Cast can alter the speed of the impeller… take a look, it’s very good

[Quadrille in JB]

Cast does not alter the impeller speed, it simply allows you to change the multiplier in the impeller to speed calculation.

My DST810 read 1.5 knots too fast when I first installed it. Cast has a calibration feature to correct any speed offset caused by hull configuration, etc. even though it is somewhat difficult to get right. I think it even has a 2-way feature that allows you to overcome any current while calibrating the instrument to agree with your GPS SOG which is always pretty much dead on.

Always believe your GPS SOG as it has nothing to do with any currents.

[Fuss]

Originally Posted by Quadrille in JB

Cast does not alter the impeller speed, it simply allows you to change the multiplier in the impeller to speed calculation.

My DST810 read 1.5 knots too fast when I first installed it. Cast has a calibration feature to correct any speed offset caused by hull configuration, etc. even though it is somewhat difficult to get right. I think it even has a 2-way feature that allows you to overcome any current while calibrating the instrument to agree with your GPS SOG which is always pretty much dead on.

Always believe your GPS SOG as it has nothing to do with any currents.

Oh, that’s good to know…I thought the cast app had an electric motor to speed up the impeller and perhaps also a brake to slow it down accordingly…so much technology in such a small device, no wonder the early DST810 versions often stopped working!!

[Quadrille in JB]

Smart a—