No experience, but a comment.

A transom-mounted transducer will give you less notice of dangerous shallows. I know I would not be satisfied with that location here in our skinny waters.

I have installed Garmin transducers in-hull in my last 2 boats(including present c36) with no problems.Accurate soundings to 600+ft.Made an epoxy "well" with circles of silicone bead.This one is port side of engine,slightly aft and up from packing gland.Make tests by putting transducer in a baggie with water in it...move the trans/baggie/water around in likely areas with the unit on..flatter areas work better..in any case the tducer must be mounted level in the "well",stabilized with tape then pour epoxy....btw,any transducer will work,does not need to be the in-hull td.

Don't know if I should start a new topic, but this question applies to sonar transducers.

I'm adding a secondary thru-hull transducer as part of my new Garmin 740s gps package. So, I'll then have two separate transducers sending sonar signals to the bottom and back. Any chance these two separate units will confuse each other - receiving echos from the other transducers? The two transducers will be about 5 feet apart, on the bottom of the hull.

Thanks!

Yes, two transducers operating simultaneously would confuse each other and produce false readings. Depth is determined by the travel time between the ping and the first received return from the bottom. False shallow readings would result if a ping is heard during the listen interval. The path could be through the water or through the hull. If through the water, the beamwidth of the transducer is determined by its diameter in wavelengths. A 4 wavelength transducer would have a 15 degree beam. At 200 Khz, the diameter would be 3 cm, at 50 kHz, the diameter would be 12 cm. If through the hull, most likely, any ping before something from the bottom would be counted as real.

Thanks for the info! I'll just swap out the 22-yr old transducer and unit, then replace it with the new Garmin system. That'll force me to mount the Garmin display by the helm, a more appropriate place for the gps, radar and depth readouts than in the cabin by the Nav station, anyway.

Yes Impag is correct. We currently have 2 transducers in the bottom and one is in the front and one is under the sink area. The one in the front is hooked up to my Nexus instruments and the one under the sink area is hooked up to our Garmin chart plotter. But when turning on the nexus instruments that depth sounder will not read correct if the Garmin is on. But in the other post about installing a inside sounder was great to see as I have that same issue. The one for the garmin went out 3 months ago and I now depend on the front one from the nexus as I did get a replacement transducer from Airmar which is the same as the one for the Garmin. Currently I have it in a bath of veggie oil as I have been talking to Garmin via phone trying to sort out the issue in getting a clear signal. As of right now it is not working well and my next move is to try and move it further aft as I wonder if the wing keel is affecting it or is it to thick under the sink area.

thinking about getting TackTick depth/speed and wind system so should I cut a hole or not?
I'm in a lake in north east Oklahoma that I've sailed for 20 yrs so I know where to go and where not to go. But I do want to be really sure though.

Thanks Impag
This Forum just saved me the 3-year membership cost many times over. Never would have occurred to me that "dueling" transducers could be a problem. I'm not brand new at this, but obviously still have much to learn.
Have a Garmin "fish finder" mini-chart plotter that the PO installed after the old depth display went TU. Now for depth, the Garmin must be turned on. Was going to replace the existing speed transducer (which lives only a foot or so from the Garmin's) with the Nexus combo speed/depth, along with their wind speed and direction unit. Now it seems this won't work for accurate depth info? Now what? Any advice?
Speaking of Spanky's Tacktick wind suggestion, he might want to inquire on the Forum as to the recent experience of others in the unlikely event they have had okay luck with them.
After having two of those POS Tacktick wind systems (well actually three, since the second one was DOA in the box - and Defender refused to take it back, telling me to call Ocean Equipment) on two different boats - NEVER again. The so-called customer service of the wind units from Ocean Equipment was absolutely atrocious. The tech had so many failed units on the bench that he was unable to successfully locate the one I had sent. The problems, he said, were intermittent and impossible to diagnose.
When they worked, both of the display units were fond of switching back and forth between True and Relative wind, and usually locking up on the former. Since there was no GPS input (and no way to program the units accordingly) they simply didn't work until I went forward to toggle the display back to Relative Wind, which repeatedly switched back to True Wind and nothing on the display. Neither units worked in Friday Harbor thanks to interference from something. You couldn't give me one for a present.
I do have a friend in Friday Harbor with the Nexus W/D/S system who is very happy with it.
I'll be curious if others report that Tacktick or Ocean Equipment have cleaned up their acts since three years ago.
Hope this helps.
Jack
Often wrong, but never in doubt

This discussion overlaps some questions that I have relative to depth transducers. I am installing a new Ryamarine gps/chartplotter. For me to get depth on this unit I would have to install an expensive sounder module which would give me full fishfinding capabilties along with depth. Since I am primarily interested in depth, I was thinking of installing an inhull transducer that would work with my tridata.
I was curious if others use and like the fishifinding features and feel it is worth the extra cost to install it? I was also curious where most install their inhull transducers and get the best/most consistant readings. So far I've read about placing it under the sink and aft in the engine compartment as well as under the vbirth?

I installed my inside the hull dept finder under the V-birth about two years ago. It works well. Remember after a depth finder is installed it has to be adjusted. I adjusted mine for waterline depth. Some skippers adjust theirs for depth under the keel.

I sail in a lot of skinny water and the depth finder has never failed me...as long as I keep an eye on it. When I run aground it is reading about 4.5 so I know it is adjusted properly.

Thanks Mike,
I guess that I'll have to find a good spot to run aground after it's installed so I can adjust it

[QUOTE=pmeyers;8164]Thanks Mike,
I guess that I'll have to find a good spot to run aground after it's installed so I can adjust it[/QUOTE]

You could do the first and forget the adjustment.

Think about it. (This comes up all the time with depth sounders.)

If you KNOW what # the sounder reads when you hit, that ALL you need to know, regardless of whether it's water under the keel or from the waterline.

When we bought our boat, I simply found a nice soft spot of shallow water and slowly ran the boat towards it. When it hit, it read 4.4.

That's all I needed to know.

From that, you can do all the math you need for tide height changes from chart datum.

For example, we have a great anchorage that has a shallow bar crossing. From doing the math and experience, I KNOW that if the tide height is 00.00 or less, I can't get in or out. How? By going over the bar and reading the sounder, and knowing the tide height (when it's higher, of course), I just did the math.

I was kidding, but what you say Stu makes sense.