Thread: Can you test a new fish finder for proper operation w/o putting it in the water?

It has to be in the water

Barnacle Bill is right: it has to be in the water to verify the installation and operation is correct.
I do have a concern though. You stated:
“Transducer is mounted inside the hull, sitting on a bed of about 1/2" marine goop with (hopefully) no bubbles.”
I am hoping that there is not ½ inch of marine goop under the bottom of the transducer. The thickness of the layer of material (epoxy, marine goop, etc.) that is surrounding the transducer does not make any difference as to the operation; it is the amount of material that is between the transducer and the hull that makes all the difference. The thinner the better here and of course – no air bubbles.

find a container that you can mold/modify to fit fairly tight to the floor (large foam cup, etc) and make a swimming pool for the transducer. You will probably have to do this everytime you use it to fool the unit into thinking its in the water. Plumbers Putty will work as well (from Lowes/HD), just have to build it high/deep enough to have the xducer under water. Then fill it up with tap water, and see what happens. The putty will not harden from what I've read, but you will have to "fill it up" everytime you go fishing.

We used to "test" our ice fishing units by hanging the transducer off the edge of the table....like a plumb bob....it has to be in-line up and down(level) because air is not as dense as water (sound travels better in water)your mark or return signal is about 4 times the distance...off a standard height table around 30 " I get a signal at 10 '...so off your saw horses 4 times the distance you should get a blip....the only problem I can for see with this is if your transducer is not completely level you'll have to slowly rock it back and forth to "see" the blip.....start with your gain or sensitivity up to get a return...hope this helps

That could work with a manually controlled sonar unit but less so with an automatically controlled sonar unit like the PMax 175.
The output power of the unit would affect this as would the material that the floor (or floor covering) is made out of.

Greg can you enlighten me on that unit...it has no control for sensitivity??...should still shoot through the hull correct.??.. does that application then make the entire under side of the hull a receiver... just curious.....never mounted a through hull transducer myself...but have a good command of depth finders and their workings...never tire of learning...

It does have a Sensitivity control Professor but it is more like an offset control as opposed to a direct control. All you do when you adjust the Sensitivity menu is offset what the unit is automatically setting the sensitivity to. There is no direct control with the actual receiver sensitivity as all you are doing is adjusting what the unit is programmed to display. When you stated “ice fishing units” I thought about a mechanical flasher type unit. These used to have (I have not opened one up lately) a direct manual control for the receiver sensitivity such that if you went into deeper water you may not even get a bottom reading. Try that with a PMax unit and it will automatically vary the transmit power, receiver sensitivity and some filtering to display a bottom reading (that is why some sonar units will show hundreds of feet deep when the transducer loses contact with the water). It is this same ‘automatic’ programming that works against being able to reliably test the PMax and other units out of the water.

It still should shoot through the hull of a kayak (or fiberglass boat) as long as it has a good transducer installation.

Only the hull directly under the transducer becomes the transmitting/receiving area. The entire hull could be a transmitter/receiver for any sound but the frequency, power and returned signal strength would not match what the sonar unit is looking for.