Erratic Depth Readings

[TBOT422]

On our latest cruise, we had erratic depth readings in water depths less than 8 feet. In depths greater than 8 feet readings seemed normal, steady and accurate. Below 6 feet the gauge would generally start up with just dashes for a depth. When going from 8-9 feet to shallower depths, the gauge would loose track of the bottom and flash, sometimes showing 14-15 feet when I knew full well that the depth was 5-6 feet. The ST60 manual says this problem could be associated with a poor electrical connection of the transducer to the gauge. After returning to our dock, I cleaned the connections, but as the dock depth was 12 feet at high tide, I didn't learn much. This evening at low tide, the gauge showed 17 feet when turned on and took about 10-15 minutes before sinking in to the proper 9 foot depth cycling from 16-17 feet to 9-10 feet several times. Is it possible that bottom growth on the transducer could be contributing to the problem? Does the transducer protrude through the hull or shoot thru the hull? I can find no other electrical connections from the transducer other than those directly at the gauge at the helm.

Any thoughts or suggestions would be appreciated.

[KenKrawford]

Gary my Raymarine transducer is mounter in a cutout of the hull and I suspect yours is too. Pull up the small access panel on the floor of the V berth to verify.
Unless your transducer is completely covered with growth, it still should work.
The only way to determine whether your problem is with the transducer or the display would be to buy a new transducer, connect it to the display and dangle the transducer in the water. If you get a correct reading, there’s your answer. Unfortunate you’ll need to haul your boat to install the new one. Let us know what you find out.

[wolfe10]

Yes, on the 2004 350, the depth transducer has a separate thru hull. A separate one for knot/temp next to it. Accessible by lifting the sole in the forward cabin.

[TBOT422]

OK, I bought a new depth transducer, plugged it in and dangled it over the transom. I slowly lowered it into the water and depth readings were accurate all the way down. So now its time to install it. Haul out is next week. I plan to cut the wire to the old transducer, then install the new transducer. Hopefully I can use the old wiring to pull the new wiring the full length of the boat.

If anyone has done this, do you have any idea where the transducer wiring may run, and are there any locations along the way where the cabling may be visible or reachable to make intermediate stops or inspections? I suppose I may have to remove the cover under the helm on the ceiling of the aft cabin, but would certainly like to avoid that if at all possible since I have converted the aft cabin into the aft garage with lots of storage and shelving. I can see where the cabling leaves the forward area where the transducer is, but I don't see it under the head sink, or along the side of the bilge, or anywhere else until it connects to the gauge. Does anyone have any idea of where it runs?

Here's hoping that some nice person didn't tie wrap the depth transducer cable to the speed transducer cable somewhere along the way.

[KenKrawford]

Gary I replaced my speed and depth transducers a few years ago and used the method you are considering. That part was easy and straight forward. I used electricians tape to secure the new and old ends together. Use plenty of tape and wrap it as tightly as you can. For me the hardest part was threading the cable through the tubing of the pedestal guard. I tied a messenger line to the end of the old wire at the back of the instrument display and pulled that down to the bilge and then connected the messenger line to the cable coming from the transducer. It's still a tight fit.

[TBOT422]

I tied a messenger line to the end of the old wire at the back of the instrument display and pulled that down to the bilge

Where in the bilge? Somewhere near the transom? Did you access that area via the panel on the ceiling of the aft cabin, or through the lockers in the cockpit (I.e. above hot water heater)?

Does that imply that you were easily able to pull the new cable aft to somewhere in the bilge by using the old cable as the 'messenger' line?

[scott.monroe]

Good morning Gary,
I installed a new speed transducer recently (as part of a full electronics overhaul to NMEA 2K) and with some hunting found the path that the installers took for both the speed and depth transducer. I opted to use an electrician's snake to run the transducer cable. Running it from the thru hull aft isn't too bad. It went behind the head, and under the port bench up to the battery box, which is easily accessible by lifting covers. From there it took some hunting. The 2" PVC conduit pipe that runs aft is accessible by removing the battery switch panel under the desk. Again used a snake to pull the cable from behind the batteries and to the pvc conduit and then it was easy to pull it aft through the pipe using a snake. Once in the aft lazarette its just a matter getting up to the pedestal, which will require removing the cover in the aft berth.

Hope this helps,
Scott

[TBOT422]

I poked around a little without dismantling anything and I can't see anything that appears to look like a transducer cable anywhere along a likely path. There is no visibility behind the head. There doesn't appear to be anything under the head sink where some other wiring runs. I don't see anything behind the port settee battery area or above the port window behind the large table storage location. I did see one wire similar to the transducer cable in the port cockpit locker (where the main power breakers are), but I think it is the GPS antenna cable as it is tie wrapped to the TV antenna cable. Lots of tie wraps everywhere I looked. I can't really imagine the transducer cables run the full length of the boat and aren't tie wrapped to something somewhere that is inaccessible. I guess I will find out. After the haul out is done and the transducer replaced, I will begin removing the access panel under the helm on the ceiling of the aft cabin and see what I can find out. Something tells me this simple task will take a week.

[KenKrawford]

Gary it's been quite a while since I did my replacement so the details are a bit foggy right now. This project was part of a lightning strike repair and I had quite a bit of the boat torn apart at the time. The only thing I'm fairly certain of is the cables pulled easily. Have you taken the mattress out of the aft cabin and poked around by the fuel tank? I have a vague recollection that they were in that area.

[TBOT422]

Thanks Ken,
That was going to be my next place to poke around. But, that is going to have to wait. Haul out is today. We have converted the aft cabin into the aft 'garage' with lots of storage and removable shelving. So I figure it may take me a day to unload the aft garage, and get access to the fuel tank area and under the helm. I will post what I find, so that others may have a road map if they ever need to go through the process.