Transducer Signal Loss

[Tug]

It seems that i am having the same problems with my newly installed AirMar P66 transducer as i did with the last transducer i had on my boat.. I am wondering if the problem is because the transducer is mounted on the Port side. The problem is that i loss the signal when i trim the motor up to the point where the boat is running at optimal plane and RPM.If i trim down to a point where i feel the boat is dragging a bit i regain the transducer signal. Another annoying thing is that i can be be anchored,i have the bottom, i bring up the anchor and slowly move off at trolling speed and suddenly i loss signal again. I can continue to proceed at trolling speed for a minute or two before i acquire the signal again.The flat hull of the C-Dory creates a lot of turbulence and that may be part of the problem.The transducer was installed as per instructions, for those who have installed the Airmar P66 transducer on their C-Dorys do you remember if you used the wedge. ( shim ) that came with the transducer.I plan on moving the P66 to the Starboard side but that may not be the solution to this problem. Tug

[starcrafttom]

Tug, I have never had a transducer that always saw bottom. In fact most will lose bottom as you trim up the boat. Its just to much air and turbulence passing under the boat.

make sure the bottom edge of the transducer is at least a 1/4 to 3/4 of a inch below the hull. This puts it in clear water. the only other way is to have a thru hull unit put in and even then you will loose bottom at high speeds. its just normal.

[Aurelia]

Before mounting our latest Garmin transducer, I rigged it up on a board and C-clamped it in various positions on the transom to see how it acted. I could not get a reading on that thing above 1knot anywhere near the edge of the hull while not extending it bit below the hull edge. I ended up putting the new one where the old one was, at the lowest point of the hull and extending about 1/4in below the hull edge. I feel like it is a bit exposed but with it mounted that way I get a solid reading up to and even while planing sometimes.

[Wandering Sagebrush]

Tug, when I had a Lowrance system on my boat, I rarely had a good solid lock on the bottom when at speed, and often even when trolling.

I put a Raymarine C80 system, including the depth module on the boat, plus I installed a Humminbird gps/sonar as a backup. I now rarely lose contact with the bottom on either system. I typically will leave one of the sonar units off so that they don't interfere with one another. Now, about the only time I lose bottom contact is when there is any sudden change in depth, like in the canyons at Lake Powell.

With the transducer for the C80, I was very careful to install just as directed. It is about a foot away from the leg on the Honda 90, and just a tiny bit below flush with the hull. The Humminbird transducer is outboard of that. Again, just a tiny bit below flush.

I think that placement of the transducer is critical. If there is any chance that it is located in an area where there will be air bubbles instead of a clean flow of water, there will be problems. BTW, when I had the Lowrance system, the transducer was as far outboard as I could get it... Thinking that getting it away from the engine was best. Obviously, a wrong placement.

[Sarge]

The transducer on my boat sits quite low, maybe 3/4" and it works awesome, well it did until recently when I lost the bottom at all but a dead stop. Pulled the boat out and found the transducer hanging on by the wire! I guess I ran over something. I don't remember any loud bangs.

As was said earlier, placement is important.

[tpbrady]

My experience with the Raymarine C-80 DSM30 is similar. The transducer is about 1/2 below the hull. Losing contact with the bottom is more a function of depth than speed. In water 100 ft or more I lose contact generally above 20 knots. Yesterday I recorded a depth of 1120 feet while at 3 mph. That I thought was impressive.

[Tug]

Thanks for all the replies and information. The next time i pull the boat i will lower the transducer from 1/4 " to 1/2 " and see what it does. Its a little stressful when your in a shallow water channel and the transducer decides to go on strike. Tug

[Captains Cat]

[Alok]

Just a few thoughts about my own experince with the Raymarine C-80 DSM 30 transducer on my TC 255 which was kept in a slip year round in hot, humid Texas weather. Deep water is not an issue in Galveston bay or in the intra-coastal waterway- we consider 12 feet to be "deep." Grounding, though, is an occupational hazard and if the transducer loses bottom the pulse rate begins to go up...

Overall, the transducer has served me well. There are four situations in which it would lose bottom:

1. Following a towboat in a narrow, shallow channel because of the silt kicked up by the towboat's big engines.

2. When the transducer had barnacles on it. This huge problem was completely eliminated by putting a coat of regular bottom paint (Micron CSC) on the transducer every time I touched up the boat. Did not seem to harm the transducer housing or affect its performance in any way. By the way, the regular "transducer paint" did nothing at all. In fact, Texas barnacles seem to regard it a a special treat.

3. In rough water, the transducer can "kick up" out of horizontal position. It needs to be pushed down until it clicks back into its normal position. This can be checked for and done on the Tomcat by lying flat on the Armstrong bracket and reaching waaaay down.

4. The pins on connectors on the transducer module inside the cabin need to be cleaned periodically otherwise the transducer will act flaky

[Matt Gurnsey]

Also be sure that the trailing edge is lower than the leading edge so that there is no low pressure area on the transducer face at speed.

[Tug]

Went out fishing this morning and the transducer ran flawlessly. The only thing that i did differently this morning was i didn't trim the bow up as far as i usually do. There must be a sweet spot where the boats is running level with the transducer. I will still lower the transducer a 1/4 " the next time i haul the boat.

Where is my new trailer....3 weeks delivery time is now six weeks this coming Friday. Maybe they build them in China!

[NCPete]

After struggling with similar issues of poor operation from the transom mounted transducer, I removed it and mounted it in the small bilge inside the cabinets under the stove. I contacted Garmin and they said it would work fine if it is mounted in an area where the hull is not cored. I tested it before mounting and the readings were OK. It still reads water temps also but it take a few minutes for the hull to catch up with the water temps. There was enough room in the small bilge to allow me to epoxy it to the hull next to the pump.
Now I have flawless performance.

[Catch 22]

In general, is there a speed that a transducer should still perform at before loosing signal. I seem to lose the bottom at about 13 knots. I wish it was high so that in unfamiliar water I could cruise faster and feel comfortable...At what speed does your transducer lose bottom?

[starcrafttom]

Kevin, along with all the other thinks listed to check for you should check to make sure your unit is not in front of the skeg on your boat. You have a older flat hull just like I do and you should have 2 skegs under your hull. If the unit is in line or to close to the skeg it will cause turbulence that will degrade the signal at speed.

[Tug]

Went out fishing 5:30 AM, took me a hour to do 18 miles because of the heavy fog. The transducer was not working very good at all ,i kept losing the bottom,at all speeds. My next option is to lower the transducer,move it to the Starboard side and also make sure that the transducer is not in-line with the skeg. Tug