Depth transducer liquid, water or oil ?

[Ian_Edwards]

He's talking rubbish, it's nothing to do with air bubbles. The reason for not using silicon is that it absorbs the sound waves and gives incorrect readings. The thicker the silicon, the greater the error.

It's also not just about not getting 100m readings. The readings can be wrong in shallow water too.

Paul, you correct about it absorbing sound, its a very anisotropic material, and because of the mismatch in impedance it'll cause a lot of reflections in the interface between the transducer and the water outside the hull. That will mess-up the waveform on transmission and reception, probably making the pulses a little longer that they should be, with slower rise times, which could give a very small error in very shallow water.
But totally wrong about getting a incorrect depth, the depth is calculated by multiplying the time between the transmission and reception, multiplies by the speed of sound in water, approximately 1,500 m/sec. Having silicon between the transducer and the hull would change that in any meaningful way, you'll just get a lower power messy pulse, but it's still likely to work.

 

[anoccasionalyachtsman]

He's talking rubbish, it's nothing to do with air bubbles. The reason for not using silicon is that it absorbs the sound waves and gives incorrect readings. The thicker the silicon, the greater the error.

It's also not just about not getting 100m readings. The readings can be wrong in shallow water too.

Silicone thickness in my case varies from more or less 0 to maybe 1mm into the weave of glass.

 

[bedouin]

Silicone thickness in my case varies from more or less 0 to maybe 1mm into the weave of glass.

That might cause the depth to be out by up to 1mm - could be dangerous.

 

[salar]

I need to think it over, but am I right in thinking that the water more or less envelops the foam?

The container box would probably hold half a litre of liquid but the foam is so dense that about an egg-cupful poured over the transducer was enough. I was surprised how little went in, I though the foam would be more spongy even though it is closed cell. The liquid needs to be deep enough to fully cover the face of the transducer, more is better than less obviously. I filled it up and the lid of the junction box has a rubber seal so that liquid isn't going anywhere.

 

[Refueler]

The container box would probably hold half a litre of liquid but the foam is so dense that about an egg-cupful poured over the transducer was enough. I was surprised how little went in, I though the foam would be more spongy even though it is closed cell. The liquid needs to be deep enough to fully cover the face of the transducer, more is better than less obviously. I filled it up and the lid of the junction box has a rubber seal so that liquid isn't going anywhere.

Just asking ... given there are different forms of transducer - I assume this 'box' is designed more for the puck style low profile fish finder style ? The older more traditional vertical threaded stem and bulb end would be a bit too high / big for this ??

 

[salar]

Just asking ... given there are different forms of transducer - I assume this 'box' is designed more for the puck style low profile fish finder style ? The older more traditional vertical threaded stem and bulb end would be a bit too high / big for this ??

Yes this is for the puck/transom mount type of transducer. The vertical threaded type are not older (I have one of those too) they are the ones designed for mounting through the skin of the hull. You can mount them internally in exactly the same way as the "puck in a box" but instead of using an electrical junction box, use a section of drainpipe cut at the correct angle and glued to the hull so it is vertical. Fit a cap to the tube with a blanking fitting. You can mount the transducer inside the tube with a foam holder on the same way, then fill with liquid.

 

[Refueler]

Yes this is for the puck/transom mount type of transducer. The vertical threaded type are not older (I have one of those too) they are the ones designed for mounting through the skin of the hull. You can mount them internally in exactly the same way as the "puck in a box" but instead of using an electrical junction box, use a section of drainpipe cut at the correct angle and glued to the hull so it is vertical. Fit a cap to the tube with a blanking fitting. You can mount the transducer inside the tube with a foam holder on the same way, then fill with liquid.

mmmmmm fitting a transducer ... I've lost count how many I've done .. not only for myself but for others as well.

 

[salar]

mmmmmm fitting a transducer ... I've lost count how many I've done .. not only for myself but for others as well.

Very sorry for over-replying then ?? I'll know better next time.

 

[Refueler]

Very sorry for over-replying then ?? I'll know better next time.

No worries ... just seemed your post was teaching me how to mount one !!

 

[salar]

No worries ... just seemed your post was teaching me how to mount one !!

Plenty of people have no idea. It's difficult to tell from a post, plus, about 100x more people read posts than contribute so I tend to add something to the community when it's relevant. I learn a lot from others doing the same.

 

[Refueler]

Plenty of people have no idea. It's difficult to tell from a post, plus, about 100x more people read posts than contribute so I tend to add something to the community when it's relevant. I learn a lot from others doing the same.

No worries .....