different water temps reported from NMEA2K and garmin sonar sensor

[vas]

talking about depth sensors, I today added a garmin black box I bought s/h (GSD22) to my system.
So amidship on port side I have a N2K airmar triducer hooked up to the N2K bus
on stbrd side absolutely symmetrical I have a garmin whatever sounder sensor (6pin) 200KHz
both are obviously thru hulls 0degrees, on custom made pads to correct the slope (you call it deadrise?) of the hull there.

Up till yesterday GPSMAP4008 as well as the small GMI10s reported water temp of 17-18degrees C. I was pretty impressed and happy thinking that summer is coming.
This morning once I hooked up the GSD22, water immediately turned a freezing cold at 12-13C!

I can only assume that the data of the two dont really match and the system picks up the GSD over the N2K triducer. Other than swimming in the (for me!) freezing cold water with a normal thermometer, is there any other way of finding the real temp?
Or to put it another way, is it normal to have such deviations between two sensors effectively 1m apart?

cheers

V.

 

[jfm]

My limited experience of this is my current boat that has a pair of rather nice airmar chirp transducers. The garmin gsd26 takes data from both, and they both send temperature but of course the system only needs one temperature source. The difference is always zéro to 0.1 degree so you must have a bad thermistor or connection in one of yours

Anyway you can hot swap. The garmin menu allows you to select either transducer as the one to take notice of - you basically tell the gsd26 which one's temperature information to inject into the n2k bus. . I can't remember how but it was garminishly easy from the 80xx menu, on the gsd26 page obviously.

In your case you are putting two temperature sentences onto the n2k bus, which is a slightly different scenario. I would expect the garmin system lets you choose which to ignore. It does on my system that has 2 gps mushrooms on the same n2k bus. The menu lets me choose which gps to listen to. I'd expect same with any duplicated talker onto the bus

 

[vas]

In your case you are putting two temperature sentences onto the n2k bus, which is a slightly different scenario. I would expect the garmin system lets you choose which to ignore. It does on my system that has 2 gps mushrooms on the same n2k bus. The menu lets me choose which gps to listen to. I'd expect same with any duplicated talker onto the bus

yep, seems so...
Was away, just came back so no chance to visit MiToS again. However, I'm sure I can find the way to decide which one to pump to the N2K bus, I'm also pretty sure that last year I edited and added an offset as I thought it was way too much what it was showing. I wonder if the s/h black box GSD22 I got from the states hadn't a similar offset put that increases the diffs. I'll go through the menus carefully, zero both offsets, get a decent comparison and then decide once I get a thermometer that I can dip in the sea and watch it's value from the deck

TBH I didn't know the el cheapo B60 or whatever 6pin thruhul sensor I got had a temp on it. Nor did I thought that the GSD22 was going to get that value straight to the N2K bus, but then again, how else would it do it?

I'll report tomorrow or if dodgy when I get a reliable way to measure temps, without having to swim!

cheers

V.

PS. where is everyone, was away for 5 days and thread is still on the first page, ts ts ts...

 

[vas]

update,

if I turn the system on (N2K bus and GMI10s, DST800 and all paraphernalia getting 12V from the N2K bus) water temp is 18C
As soon as I give 24V to the GPSMAP4008 plotter and fire it up, the GSD22 wakes up and temp goes straight down to 13.4C.
Tried to choose on the GMI where to get it's temp source from, no option to choose device.

Tried from the GPSMAP marine network screen, I can indeed change from DST800 to GSD22.
Same for depth, there's 1m difference from the DST to the GSD...
Now, need to do some studying on the manuals to find if the GSD has some preset values, or PO had configured something somehow. It's interesting that I don't have to give info on what throughhull transducer I have installed (just as well as I cannot remember ). I'd have thought there should be a menu page where I can setup the internals of the GSD22.

I'll give it another go and if I fail I'll email Garmin support, there's a really nice guy that JFM introduced me to in a previous conversation on GMIs and anchor alarms.

cheers

V.