Here's one for Maine Sail Through VS In Hull Transducers

[caguy]

I have Googled and searched the internet for some empirical information on how much is lost with an in-hull transducer. Logically I can accept that some is lost, but enough to make it worth drilling a through hole. Even side by side comparison test would be helpful.
I currently have my old transom mounted transducer bees waxed to the inside of the hull and it seems to be working fine, but compared to what. I don't want to epoxy it to the bottom until I have more information. I had it transom mounted on the Mac 25 but did experience some turbulence problems at high speeds or when the ob was on.
A separate question: I have an old through hull circa 1984 in the C27 that was attached to an old unit. I snipped the wire and left it in place. Could that transducer be used or is there a problem with soldering on a new wire. I thought I read once that there can be no breaks in the cable or you will get a false reading. Haven't seen that article or warning in the last 6 years. Is that unit generationally speaking outdated or are they still made the same?
Thanks Maine Sail for all that you do.

 

[Don12364]

Many years ago when I designed an echo sounder for Raytheon the sounder's output stage was 'tuned' to suit the transducer and its co-axial cable. However this was a very 'flat' tuning response and nothing like the critical tuning of a radio set.
If you make a nice neat joint and use self amalgamating tape to waterproof it and use a similar length of cable to the original (or on the current transducer) then you will probably get away with it and even find it better than the in hull one.
Due to the relatively low frequencies involved you are not trying to make a joint that does not interfere with the characteristic impedance of the cable at that point anyway.

If the signals have to pass through fibreglass you loose signal both going out and coming back and the glass might not be solid laminate either.
Anyway what is there to loose? So why not give it a try?

Again, unless you check your position using depths, and nowadays GPS has made this unnecessary, then all you need to know is "is there enough water". So indications up to, say, 30 feet are all you absolutely must have. Accuracy is never a problem its just a matter of whether the sounder can 'see' the bottom or not.

 

[caguy]

If the signals have to pass through fibreglass you loose signal both going out and coming back and the glass might not be solid laminate either.
Anyway what is there to loose? So why not give it a try?

Again, unless you check your position using depths, and nowadays GPS has made this unnecessary, then all you need to know is "is there enough water". So indications up to, say, 30 feet are all you absolutely must have. Accuracy is never a problem its just a matter of whether the sounder can 'see' the bottom or not.

The depth sounding part is pretty accurate. I am more concerned about the fish finding feature. The hull is layed up pretty solid with out a core. It is in the engine compartment of the C27. I believe the transom mounted tranducer that I am using as a in-hull transducer is dual frequency these are the specsL Dual beam 80/200 khz 40*/14* cone angle. The unit is a GPS/Map Garmin398.

 

[Maine Sail]

Nothing wrong with "shoot through" ducers. As long as your hull is solid glass, no core, no entrapped air, not more than about 5/8" thick the can work fine.

I prefer the Airmar P-79 style, which are designed for shoot through applications. All manufacturers pretty much use Airmar for transducers these days. You may lose some performance in deep water in a shoot through application but not a whole lot... To test it try a toilet bowl wax ring to mount it temporarily then use it for a while to be sure the location is good.

Our own boat has an in-hull mounted 34 year old Radarsonics transducer that has outlasted numerous depth displays. It is currently wired to a Raymarine ST-60. I also have a P-79 installed and ready to go should the "antique" transducer give up the ghost.. They both read identically...

 

[caguy]

Thanks Maine, good to know. I assume that the dual beam comes from the garmin unit and not the transducer.
I'll try soldering up a new cable in a couple of weeks.