Another depthfinder question

[spdracr39]

I have a Lowrance LST3800 in dash unit with thru hull transducer. It will occasionally read depth but only once every 5 minutes or so whether I'm underway or not. All the rest of the time the depth reading just flashes with the last known depth. I have checked the transducer mounting and it is tight. How can I test this to see which component is bad? It is not very expensive I guess I could just buy a replacement and change the head unit first to see if it fixes it but I hate just throwing parts at problems without understanding them.

 

[pyrotek]

Re: Another depthfinder question

I have pretty much the same problem with a cheap hawkeye depth finder. I tried playing with the connection near the depth finder. On mine, they have what looks like a DC power connector like on a laptop. That didn't change anything. I preferably don't want to have to touch the through hull fitting. I'm thinking of sanding the bottom of the transducer to get any paint off it. I'll try that out for one time, and if that works, re-paint with bottom paint. That's the only idea I came up with so far. Hoping to hear better ideas...

 

[Silvertip]

Re: Another depthfinder question

Check the entire length of the hull in-line with the transducer. If there is a line of rivets or any protrusions that can cause air bubbles the unit cannot work properly. Transducers cannot shoot through air. If the transducer (or hull in the shoot through area) is coveered in slim or build up of any kind it needs to be thoroughly cleaned. Before I replaced a head unit I would borrow or buy another transducer and simply hang it over the side (at rest in an area of known depth) to see if it or head unit is the problem. Transducers are cheaper than the head unit.

 

[spdracr39]

Re: Another depthfinder question

Its a smooth bottom fiberglass hull with a factory installed transducer that reads through the fiberglass. I don't know if it ever worked correctly because I just got it. It is glued to the bottom of the bilge so I cant really clean it.

 

[Lyle29464]

Re: Another depthfinder question

My guess is a void in the glass. I would move it

 

[spdracr39]

Re: Another depthfinder question

Well I just noticed today that if I put the key in the acc position the depthfinder works fine. It will not work with the engine running even stopped in neutral. Does something need to be shielded? It is mounted near the rear of the engine away from any electrical devices. I am sure the cable runs with all the rest up to the dash.

 

[spdracr39]

Re: Another depthfinder question

Okay I have been trying to tackle this for a while. I found that the depth finder would work with the key in acc. position perfectly. If you turn the key to run with or without starting the boat no dice it will not read except every few minutes then goes back to flashing. I rewired the ground to a known good ground and positive straight to the power side of the switch and it got a small amount better but still not enough to be usable. I am going straight to the battery next and will post the results.

 

[Georgesalmon]

Re: Another depthfinder question

It often helps to run seperate fused wires direct to the battery, not following the same path as the engine harness.

 

[spdracr39]

Re: Another depthfinder question

Well I did that and it made no difference. I am going to remove the transducer and if it doesn't destroy it I will test it with the whole unit out and if it does destroy it i will replace the transducer.

 

[spdracr39]

Re: Another depthfinder question

As a final test I moved the cables away from all the rest of the harness and it made just a little difference. It would read occasionally instead of never. I am now going to remove the transducer and see if it works if I just drop it in the water. If it doesn't work correctly do I replace the whole unit or just the transducer ? Guess I'll flip a coin.

 

[spdracr39]

Re: Another depthfinder question

Latest update. I bought a Hummingbird depth finder to replace the existing one (it stopped reading in any conditions after I hammered on it and I couldn't even knock it loose) Following the directions for in hull install I could not get a reading anywhere. I will be doing a transom install if I can figure out where to put it.

 

[Thalasso]

Re: Another depthfinder question

Latest update. I bought a Hummingbird depth finder to replace the existing one (it stopped reading in any conditions after I hammered on it and I couldn't even knock it loose) Following the directions for in hull install I could not get a reading anywhere. I will be doing a transom install if I can figure out where to put it.

To be put in properly you have to use an epoxy. It has to be applied to both mating surfaces and twisted when you put it in the bilge to make sure all air bubbles are removed. If not you will get what you are describing. Some if not all depth finder that have the capabilities of thru hull also have built in the finder a program to adjust the keel angle

 

[spdracr39]

Re: Another depthfinder question

Following the Hummingbird instructions to fill the bilge with water and try it by moving the transducer around to different locations in the hull I could not get any reading in any location with the boat in the water and stationary. I mounted it to the transom and it works perfectly. No rooster tail and works at all speeds. Problem solved.