Garmin FishFinder240

[Fishin' Rod]

I have a Garmin FishFinder240. There are times when I am moving 20 mph and faster I get readings i am in water 300 plus feet when I know I am in water between 10 to 20 feet. Most of the time when I slow down my the display will stop flashing and will stabilize to an accurate display and reading. Is this a common problem with this model? I have talked to other boaters and heard they have similar problems.

 

[enfish]

I have the Garmin 240 Blue, and it's able to hold bottom readings when the boat is on plane in depths less than 150 feet or so. In deeper water, it loses bottom and we'll get sporadic readings of around 300 feet or so.

The erroneous readings are most likely caused by the transducer getting some turbulence around it at it's mounting location. Is the transducer mounted in an area with the smoothest water you can find when on plane?

 

[Fishin' Rod]

It's mounted back on the transom right on the edge of the hull. I couldn't think were else it should be mounted externally. I have heard of the transducer being mounted inside the hull. Do you know anything about that?

 

[catch22]

Transducer mounting is the key. They recomend that it should be on the starboard side of your motor, (single). Atleast a foot away from the motor. The bottom face of the transducer should be about 1/8" to 1/4" bellow the boats running surface, at the center of the transducer.

This is on the port side, but....

 

[Fishin' Rod]

That sounds about were mine is mounted. I have the boat in a slip for the season so I will have to double check were exactly it is mounted when I pull it out at the end of the season.

 

[enfish]

Catch22 has it right about location. It took a few tries to dial in our transducer location, moving it up and down slightly. When we first mounted it, it kicked up a big rooster tail and did not read anything when on plane. Here's a photo that shows the mounting location, though not in great detail:

The inboard top edge of the transducer is about even with the hull. That's just the location that ended up working the best.

 

[Fishin' Rod]

Again, that about were mine is but I won't be able to tell until I pull my boat. So I guess I will have to tweak the location of my transducer.

 

[catch22]

I have heard of the transducer being mounted inside the hull. Do you know anything about that?

You can mount your transducer inside the bilge area, if the transducer has a relatively flat face. This method is called, "shoot thru". If it's not flat, you'll need to purchase a shoot thru, or "puck" type. You will lose water temp and speed, unless they have seperate pick ups, which are mounted outside, where your original transducer is, (not sure if that's available for the 240). You will also lose some transmitting power, but imo, the 240 would be fine. I had one and had to adjust the gain down to 40 - 50% because of all the "noise" on the screen. A Garmin service tech actually recomended that.

If you decide to do the shoot thru set up, you should be able to find a decent flat area infront of your bilge pump/float switch. Clean the area with acitone, sand it a little and clean again with acitone. They recomend that you use an epoxy to mount the ducer, but you really don't need it. Just use a good marine sealent like Life Seal or 3M's 4200. This way, if you ever need to remove or replace it, it won't be too difficult. I've done a few like this and they worked out great.

Since your in a slip, this might be a good option. Leave your existing transducer in place, purchase and mount the shoot thru ducer. Just disconnect your transom ducer and plug in the shoot thru. You can deal with the transom mount later.