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Accurate water temp.

Old 06-26-2017, 11:20 AM
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Default Accurate water temp.

I have a dedicated Sitex temp gauge on my boat along with a Raymarine E120 with a B258 transducer. I was out fishing Friday and the temp on the Sitex said 64.4 degrees while the Raymarine was a 67.3.
How would one go about determining which is right.
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Old 06-26-2017, 01:28 PM
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Set at the dock with a pool thermometer on a string... Drop it down in the water and calibrate one or both to match the mercury thermometer.... You could probably even use a kitchen thermometer dipped into water. The theory with thermometer on a string is you get it into the water at a depth comparable to your temp sensor.


Another sometimes more accurate, other times not. Get a digital laser thermometer (like HVAC guys use) point at the water and pull trigger.... Use that temp to calibrate. Those things are super accurate, but depending on turbulence and sunshine sometimes the top layer of water is slightly warmer than under the boat.
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Old 06-27-2017, 01:02 AM
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Are they always that far apart, even underway? Or only when idling and perhaps one sensor is closer to the warmed engine exhaust and/or in sunlight?
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Old 06-27-2017, 07:07 AM
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Originally Posted by TTaxi View Post
Are they always that far apart, even underway? Or only when idling and perhaps one sensor is closer to the warmed engine exhaust and/or in sunlight?

I added the Sitex this past off season, did not compare them before, (need to go to another page on the E120 to see temp).
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Old 06-27-2017, 08:11 AM
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no idea why a pool thermometer would be more accurate than a thermistor. I would guess some are and some aren't.

check to see if you have a nearby noaa data buoy, and if so, take the boat over close to it and use that to calibrate.
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Old 06-29-2017, 04:17 AM
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My Garmin always reads 2.5 -3.5 degrees warmer than my Lowrance. I don't know which is right.
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Old 06-29-2017, 09:03 PM
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Originally Posted by general View Post
Set at the dock with a pool thermometer on a string... Drop it down in the water and calibrate one or both to match the mercury thermometer.... You could probably even use a kitchen thermometer dipped into water. The theory with thermometer on a string is you get it into the water at a depth comparable to your temp sensor.


Another sometimes more accurate, other times not. Get a digital laser thermometer (like HVAC guys use) point at the water and pull trigger.... Use that temp to calibrate. Those things are super accurate, but depending on turbulence and sunshine sometimes the top layer of water is slightly warmer than under the boat.
pool thermometers and laser ones are not all that accurate from my experience
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Old 07-03-2017, 11:55 AM
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So the boat is in the water for the fourth of July weekend, I walked the docks asking several people what temp their transducer was showing, 5 out of 8 showed the same as my Sitex one Garmin was 1.2 degrees higher a Furuno was .point one higher and another Raymarine was point two lower.
I calibrated the Raymarine to match the Sitex.
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