Transducer Angle

[TunOFun]

On the way to Browns on Saturday my sounder (Lawrance LCX18C) lost bottom at about 170 metres whilst trolling. I stopped the boat and with the boat at rest the sounder found botom again. Just wondering if you think it maybe the transducer angle which may be causing this. The sounder is supposed to be capable of reading to 915 metres. I fiddled around with 50 and 200 megaherts with 50 not having much luck finding bottom at all. Possible transducer problem?? Any advice??

[Ken A]

Without knowing your set up it's hard to say but if your getting air bubbles around your transducer at trolling speed that can cause this problem.

More info on your set up would help.

[Wetpatch]

I have found with my Hummingbird that if the angle is out the bloody thing would lose all its bearing and give ridicilous depth until I stopped

It was trial and error till I found the happy ANGLE just be careful as hanging out the back of the pod can be fun trying not to fall in

Edited November 14, 2005 by WetPatch

[pogo]

Angle might be a problem, but if its off by too much youll get a incorrect depth reading all the time, you can check this by using a chart and the gps to check the depth, another problem can be the angle your boat sits at different speeds, if your trolling at a speed where the boat sits up at an angle this can fire the sounder pulse forwards and at certain speeds the pulse from the transducer hits the bottom and reflects further forwards ( think like a cushion shot playing pool) and doesnt get picked up by the transducer on its return cause the signal comes to the surface in front of the boat, this is usually only a problem in deep water

200 Mhz is the best for deep water, the pulse penetrates better and if you check your manual you will probably find that the 200 Mhz pulse is at a 10 or 12 degree cone angle where the 50 Mhz signal is at 30 to 40 degrees cone angle, this wider angle means that the pulse doesnt penetrate as far, or is dispersed faster if you like

the old 1 in 60 rule works, with the 10 degree cone angle your sounder is generating a pulse that will be about 10 metres wide at 60 mtres, 20 at 120, 30 at 180 etc, whereas the 50 Meg transducer will be 30 at 60 etc

you can run this rule on where the signal ends up as well. if your boat is sitting up at say a 6 degree angle( compared to sitting level) as youre trolling, the signal will reflect off the bottom at 12 degrees so the core of the signal will return to the surface 12 metre ahead of the transducer in 60 metres depth, 24 in 120 and 36 mtres!!!! ahead in 180 mtres. If your boat sits 12 degrees nose up at trolling speed the core of the signal hits the surface 72 meters in front of the transducer

If you can trim to stay level you might should be able to hold the signal better. Hope all this makes sense, its easier to explain with a pen and table napkins and beer

Regards Pogo

Edited November 14, 2005 by pogo

[Guest Jewel]

This is straight off the Lowrance website, sorry Pogo not tryng to have a shot at you as you are sortof there!

"Typically, high frequency (192 or 200 kHz) sonar units provide the best resolution and definition of structure and targets. They excel at showing minute details of the underwater world. 50 kHz units have much greater depth penetration capability, but show less definition. 50 kHz transducers also usually have a much wider cone angle than 192 or 200 kHz transducers."

This is all true as Pogo has said, AS LONG AS YOUR Tx IS POINTED IN THE RIGHT DIRECTION!!!!!

If it doesnt get back, it doesnt matter how deep it gets!!!

Additionally you may find that your settings could use tweaking to get the most out of the unit.

[pogo]

D'oh,

Of course you are right jewel, lower frequencies penetrate better than High, sorry about that.

The minute I reread my post I spotted the obvious error.

regards Pogo

[Guest Jewel]

Its a shame really this would be a great discussion with a few and a coaster!!!!

Whos shout!!!

[TunOFun]

Thanks for the advice guys, ill make some slight adjustments to the angle the next few times i go out and see what works best.

Cheers