Should this Lowrance 3500 DF only get a reading if in the water? Odd behavior.

[spencerkechi]

Should the Lowrance 3500 only provide a reading when the boat is in the water? We bought a 2000 year boat with the Lowrance in-dash 3500 depth finder. For whatever reason, the transducer cable was cut, so I had to buy a new cable/puck (part PD-N). In the process of trying to figure out where to epoxy it (near the original puck in the engine bay), I noticed something strange. If I just set the puck on the bottom of the boat, it flashed .5 ft (no signal). If I flip it upside down, it reads 8 or 9 feet. If I hold it over in a 2 foot bucket of water, it reads about 2 feet.

Does the boat have to be in the water to read correctly? The only other depth finder we have experience with is the Hawkeye with an external mount. That depth finder always read correctly in or our of the water and we have owned about 3 of those. I realize there is some air between the puck and the bottom of the boat until it gets sanded and epoxied down, but I am worried that something else is wrong, and that once I epoxy the puck down, I am "stuck" with what I've got. Why would it have a reading when I turn it upside down? There is a lot more air between the top of my barn and the top of that puck than there is between the bottom of that puck and the fiberglass boat bottom. Any advice on this?

 

[GA_Boater]

Transducers do need to be in water to work. No matter what readings you get when it's out of water are meaningless, except temperature. I've never had a transducer work in air and that's a few different makers.

As far as working upside down, the sonar needs something to reflect the sound waves off of. Maybe it's reflecting off the roof - Got a metal roof?

 

[spencerkechi]

It is a metal roof in my barn.

 

[sam am I]

As far a testing beforehand and short of just dropping the xducer over the edge of the boat or a dock in the drink, I've heard some guys having great success in-shop pre-testing their units by submerging and aiming the xducer down a stood up on end length (couple feet at minimum, 6' stick perhaps would do I thnk) of PCV pipe that's capped off and filled with water.

 

[GA_Boater]

I've done that but only used a bucket. As soon as it hit the water, I got a reading.