Depth Transducer problem

[Neddie_Seagoon]

When underway my depth sounder rapidly and erratically cycles through readings - I have learned that the deepest reading it gives is probably right, but I assume that the tranducer is not adequately mounted - it is stuck to the inside of the hull in a glassed-in oil bath. At first assumed that there was a lack of oil - but there is plenty. While it is stuck to the hull it can be wobbled a bit - so it's not as stuck as it might be. I thought about pulling it free and suspending it in the oil bath, but before I do that I thought I'd ask for suggestions. I have only used it under motor so far - could the problem be electrical interference (no evidence on other devices such as radio)? Going slowly (3 knots) in calmer water it is more stable, going faster (6 knots) in open water it is totally erratic. It is mounted in the bow a little ahead of the keel.

Any thoughts?

Ta,

Steve

 

[dmayes]

Possibly bubbles flowing past the transducer. The better results at a slower speed would indicate this. Try taking the transducer out of the oil bath and putting it into the water over the side of the boat (or the stern) tied to a stick. This should show how the electronics perform. If it is a steady reading, try changing the position of the internal oil bath getting it as low as possible and as near to the centre of the boat as you can, keeping the actual transducer vertical, but make sure it is not too near the keels. Also make sure that the hull is not double skinned where you eventually mount the transducer.

 

[Channel Ribs]

Sounds like the installation is iffy, shooting through the hull can be tricky to get right. As well as the stick idea, you might like to try various places inside with a lump of plasticine.

 

[simonfraser]

if it wobbles there is likely to be air between the bottom of the transducer and the water, that's no good
try resticking with plasticine or silicone, it will work before the silicone is set, so you can try different locations, away from turbulence

 

[oldsaltoz]

G'day Steve,

This is an odd installation, the oil bath method is normally used to allow the transducer to swing when the boat heels thus maintaining an accurate depth indication, but you say it's stuck (if a bit loose).

Try dropping the transducer into a plastic bag part filled with water and wet the bilge to eliminate air bubbles, then move around till you get a good signal, that's the spot to locate it, if you don't need a swinging transducer just stick it with a dob of Sikaflex, make sure no air is trapped though.

Avagoodweeknd......

 

[PBooth]

Hi, try adjusting the 'gain' setup on the sounder, increasing the gain will make the sounder ignore the echo from immediately below the transducer where there can be turbulence/bubbles that can give the effect you have. This sorted out a Nasa sounder for me.

Peter

 

[Danny]

[ QUOTE ]
I have only used it under motor so far - could the problem be electrical interference

[/ QUOTE ]Unlikely to be electrical interference but it could possibly be acoustic interference. Stopping the engine for a minute or two will tell you...

 

[pampas]

I expect that your receiver has no averaging circuit fitted, this problem is quite noticable and is commonly left out of the cheaper models in a manufactires range, unless you go.for the exspensive makers.

 

[macnorton]

I stuck a through hull fish finder transducer to the inside of the hull with silicone four years ago, still works perfect!

 

[Dougal]

I had a motor boat boat once that did this, just as you describe. Did indeed turnout to be electrical intererence from charging system. Fine at low rpm, but as soon as the old dynamo kicked in, away it went!

 

[john_morris_uk]

[ QUOTE ]
This is an odd installation, the oil bath method is normally used to allow the transducer to swing when the boat heels thus maintaining an accurate depth indication, but you say it's stuck (if a bit loose).


[/ QUOTE ] Golly, they must do things a bit different down south. I have never seen a transducer 'swinging' in oil. Only ever seen the oil used to facilitate the sound conduction between transducer and hull and onwards to the water.

 

[Lakesailor]

I fitted a NASA Clipper which is nearly the cheapest you can get and you can adjust the sampling rate, the averaging rate and the gain.

I'd certainly suspect air turbulance on the hull surface. On the electrical interference point, does it happen when sailing at 6 knots?

 

[Neddie_Seagoon]

Dunno whether it is a problem when under sail - I haven't had an opportunity to find out yet /forums/images/graemlins/frown.gif The turbulence idea makes a lot of sense, I will try playing with the gain before doing anything more drastic..

 

[Guest]

Re: Depth Transducer problem ... so to differ but ....

"This is an odd installation, the oil bath method is normally used to allow the transducer to swing when the boat heels thus maintaining an accurate depth indication, but you say it's stuck (if a bit loose)."

A proper installed transducer in-hull should not "swing" in its tube ... The tube is only slightly greater diameter than the head ... in fact it should need q resonable push to get head to sink into the oil. So much so that you should wait for oil to dissipate any bubbles so induced. One mistake some make is to put Tranducer head in and then pour oil .... No - oil first then head.
Head should never touch hull in a oil-tube installation ... it should be a fraction of the bottom ... held by its nut and tube cap.

Old oil can get contaminated ... with water / crud and that can affect its working.

The effects described by original post are most likely IMHO to the effects of wrong positioning and aeration / disturbed water under hull ...

As advised by others ... remove from tube ... hang over side and try again .... if it's still erratic - then its connection or equipment. Borrow another transducer from a friend !! Try that ..
If your head produces good reading over side ... then it's down to finding the "sweet-spot" in-hull to mount it ...... as others describe ....

 

[pampas]

I think that you will find that the clipper is fitted with the averaging circuit and the target not,at least my target isnt, perhaps on latter models it is.