# Airmar P 79 in hull transducer not reading depth



## SanDiegoChip (Jun 12, 2007)

Hi,
We have installed a Airmar P 79 in hull transducer. It is in the bilge of our 1978 Islander Freeport sail boat. 
The Airmar P 79 transducer is connected to our Garmin network and as soon as we connected it we saw the Depth on the Garmin 740 chart plotter, but with no numbers. There was not any depth readout before so we are thinking it is working on the network fine.
We followed the direction in how much fluid to add 2.4 fluid ounces and we used 99 percent Antifreeze.
We do not get and numbers for the depth. it reads like this __ __.
Any one got an idea why we are not getting a reading? 
We are at our slip in about 13’ of water. We have not gone out to test this is deeper water.
Currently in Paradise Village Marina in Puerto Vallarta Mexico.
Thanks,
Chip


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## ambianceack (Aug 27, 2006)

Is the bilge above a lead keel? If so, perhaps the keel is not allowing a good reading of the ground.


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## chucklesR (Sep 17, 2007)

Did you do the recommended test - before installing lower the unit into the water and make sure it was working?

I'm going to assume you are running the depth in through a NMEA 0183 connection - or are you straight NMEA 2000. 

I have a P79 hooked to my Raymaring e7d, excellent low cost choice for a transducer. I get depth and good fishfinder data.


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## SanDiegoChip (Jun 12, 2007)

ambianceack said:


> Is the bilge above a lead keel? If so, perhaps the keel is not allowing a good reading of the ground.


 Yes the bilge is above a lead keel. Well it is not _above_ the bilge where the transducer is over to the side but I get you point. The lead may be stopping the reading?
Thanks,
Chip


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## SanDiegoChip (Jun 12, 2007)

Hi,
No we forgot about the recommended test! We can still do that but of course we need to un-snake the cable all the way along the boat to do it  This may well be what we will have to do.

Our network is a NEMA 2000 Garmin network. The extra cable we attached to the transducer cable is a backbone cable 5 pin.
Thanks,
Chip
Chip


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## chris_gee (May 31, 2006)

Two possible points. It only shoots through a limited thickness of fibreglass, 1" from memory but check their site. No wood. I also think that the cable is fixed in length. That is the signal processing relies on a fixed known length.
I don't know the details of using a network. Just straight into a fishfinder plotter you also enter the type of transducer. You can also test it over the side before fixing it in position. I take it you have it offset to the side so the beam doesn't hit the keel (though it might if you are heeled).


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## SanDiegoChip (Jun 12, 2007)

Hi,
We will email Airmar and see about cable length.
I am not sure how thick our hull is at the point it is installed but I doubt it is over an inch.
Thanks,
Chip


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## overbored (Oct 8, 2010)

P79 is good up to 5/8" solid fiberglass
Airmar FAQ - I want to install an in-hull transducer. What is the maximum hull thickness that I can shoot through?
put it in a bucket of water it should read the bottom of the bucket. if you can hang it off the side of the boat just in the water it will read mooring depth.


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## SanDiegoChip (Jun 12, 2007)

Here is what I got 

FYI
From the Airmar FAQ

What affect does hull thickness have on the performance of an in-hull transducer?

The thicker the fiberglass the more signal is lost passing through the hull. However, our in-hull transducers are designed to more than compensate for this loss.


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## overbored (Oct 8, 2010)

the thickness does have an effect on both the max depth and the resolution. if you want to use it for serious fishing then you will want a thur the hull sensor. if only for depth to keep your keel in good shape then the hull thickness will not be a problem for the in hull sensors.


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## Kajungizmo (Aug 5, 2012)

Sorry to hear of your problems, but the best course of action is to undo what you did. Hang the transducer over the side and make sure it's working first. Then you can work out where to place it in the hull. 
Depth sounders work off of sound waves. Sound travels differently through water than it does through air. Air is the enemy of your in-hull transducer. Air in wood fibers, air in foam core, air between laminates will all hinder performance of your P-79. The keel will also hinder performance, locations forward of the keel or 2 feet away (port or stbd) are best in my opinion. 
You didn't mention, but I assume this is sitting at dock and still reading _._
If it works at dock but not underway, you're getting air (turbulence) under the hull in the transducer area. In that scenario, relocating the Xducer is the only option.

Hope this helps, 
KG


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## SanDiegoChip (Jun 12, 2007)

Thanks, that is good news about hull thickness. We have been working on out Garmin under deck autopilot. New Drive A unit and re-installing it. Soon back to the depth transducer 
I think we will:
Try adding more fluid.
Removing and hanging over side, lots of wire ties to cut and un snake the cable etc.
Then if it works add extension cable and try again.
Any way that's the plan and will keep you posted.








Shows the transducer and cable and backbone cable we used for an extension.









Installed and not quite working 
Thanks,
Chip


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## SanDiegoChip (Jun 12, 2007)

We got depth!










Yes the transducer is now working! When installing the transducer we had sanded the hull smooth and in doing that the hull in that spot became a little concave. We also bedded the transducer with silicone and this raised the housing a bit. We then put in the recommended amount of 95% or so antifreeze and it never worked. We did see the transducer on the Garmin network though. So before un-snaking the 20' cable from the bilge and then doing the water test we decide to try more fluid.









I of course I did not measure I just poured in antifreeze till it over flowed and put the top back on. The transducer then worked! So it was a fluid problem, not enough fluid. We then had to sop up some fluid with a paper towel to get the level down some and re-secured the top.









The tide is going out.​
We have a 20' Garmin backbone cable attached to the 20' (I think it is 20') cable that is attached to the transducer and this is not causing any problems.










This is the first time we have had depth in 10 years! We had a Catalina 30' for five years without a working depth gauge. And we have had this boat for five years and have sailed from San Diego along the Mexican coats as far down as Melaque\Barra-Bahia de Navidad and then back here to Paradise Village Marina in Puerto Vallarta Mexico with a depth gauge but it will be much nicer to have one now.
Thanks,
Chip


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## ambianceack (Aug 27, 2006)

Great!


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