Airmar P79 Issue

[Dino]

Hi,
I’m away cruising at the moment and my depth sounder has stopped working. It’s a Raymarine i40 Depth with an Airmar P79 transducer. I have replaced the connectors on the wires and occasionally I get an oddball reading of 4.1ft and then it flashes for a bit and then I get three dashes.
I just inspected the transducer in the hull. It’s an in-hull unit with a greenish blue liquid in it. The liquid looks dirty and it looks to be low.
Is there anything I can replace this liquid with to see if I can get it working again?

 

[Boathook]

I think that I filled my P79 up with antifreeze. Can't remember the type recommended as manual's are down on the boat. If the liquid is dirty that could affect performance along with a low level.

 

[emmalina]

Propelene glycol BP

 

[PaulRainbow]

Hi,
I’m away cruising at the moment and my depth sounder has stopped working. It’s a Raymarine i40 Depth with an Airmar P79 transducer. I have replaced the connectors on the wires and occasionally I get an oddball reading of 4.1ft and then it flashes for a bit and then I get three dashes.
I just inspected the transducer in the hull. It’s an in-hull unit with a greenish blue liquid in it. The liquid looks dirty and it looks to be low.
Is there anything I can replace this liquid with to see if I can get it working again?

As a temp fix, any cooking oil will do. If it works, change it for antifreeze before the cooking oil goes rancid.

 

[Dino]

Thanks folks, I had antifreeze onboard so I cleaned out the old gunge thoroughly and cleaned everything. Put Vaseline on the o ring and put around 75ml of antifreeze into the bath. Refitted the top and hey presto… we have depth again.
Delighted to be able to repair it on the go.

 

[Moonbeam]

Good to hear you have it fixed... just for info...Our P79 worked with just being stuck to a nice bed of window putty/plumbers mate on the inside of the hull. It was meant to be temporary install until I got the oil bath sorted, but it worked so well I left it... it was still going strong after 12 years when the boat was sold.

 

[salar]

You can use any liquid. Antifreeze is recommended because...it doesn't freeze in winter. That's the only reason.

 

[PaulRainbow]

You can use any liquid. Antifreeze is recommended because...it doesn't freeze in winter. That's the only reason.

It's obviously true that anti-freeze doesn't freeze, but the main benefit over oil is that it doesn't go rancid.

 

[graham]

It's obviously true that anti-freeze doesn't freeze, but the main benefit over oil is that it doesn't go rancid.

And that may explain the faint rotting vegetable type smell I have recently noticed in one of our boats lockers which has an oil bath depth transducer with vegetable oil in it.

 

[penfold]

The transducer for our fishfinder is fastened to the inside of the hull with about half a tube of silicone sealant.

 

[PaulRainbow]

The transducer for our fishfinder is fastened to the inside of the hull with about half a tube of silicone sealant.

Which is against the manufacturers fitting instructions. Foft sealants between the transducer face and the hull absorb some of the sonar signals and give inaccurate readings.

 

[penfold]

Wasn't me, Sir; it was like that when I found it. Seems accurate enough, although the brown water navy on the east coast may need better fidelity.