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Author Topic:   Sonar transducer location
Livingwater posted 04-22-2006 04:01 PM ET (US)   Profile for Livingwater   Send Email to Livingwater  
Looking for pictures of transom mounted transducers for a 190 Nantucket (Outrage). My 150 XL Optimax has a paddle wheel (Speed sending unit) mounted on the transom. I'm looking for the optimum location to mount my transducer for my Navman 6500 chartplotter. With the hull resting on the bunk and the existing speed sending unit there is only one other area that I could mount the transducer but it would be approx. 12" from the starboard side of the boat when I mount it onto the transom inside the strake.

Also the plug on the end of the transducer cable is going to require that a 5/8" diameter hole be drilled through the transom. (OUCH):(

Need more advise from my Whaler family :)

Livingwater posted 04-22-2006 04:13 PM ET (US)     Profile for Livingwater  Send Email to Livingwater     
Found this link:
bsmotril posted 04-22-2006 10:12 PM ET (US)     Profile for bsmotril  Send Email to bsmotril     
Rather than drill a hole through the transome for the cable, run if over the top, and then bundle it in with the rigging cables for the motor and feed it in through the same rubber boot the motor cables use. From there, you can either guide it up the rigging tunnel, or up under the stbd gunnel depending on the boat model. BillS
Royboy posted 04-23-2006 01:46 AM ET (US)     Profile for Royboy  Send Email to Royboy     
LW, Those NAVMAN plugs are huge, aren't they? I ran mine over the top as bsmotril suggests. I figure, the boat will long outlast the transducer, so why do a custom routing? I ran it over the top of the notch and then picked up the rest of the rigging.

Sounds like we are in a like state of rigging on our boats.


rumrunner posted 04-23-2006 08:23 AM ET (US)     Profile for rumrunner  Send Email to rumrunner     
Make sure you check if your manufacturer specifies a specific mounting side. My Garmin unit required a starboard side mounting, due to prop rotation.
jimh posted 04-23-2006 10:38 AM ET (US)     Profile for jimh  Send Email to jimh     
rumrunner--do you have the transducer mounted astern of the propeller? In most outboard installations the transducer is mounted forward of the propeller. When the boat in making headway, it seems very unlikely that bubbles from the propeller could be able to move forward several feet from the propeller to the SONAR transducer against the flow of water. Even at a low trolling speed, say 2-MPH, I do not think that a bubble coming off a propeller blade can be thrown upstream a foot or more against a 2-MPH flow of water.

I have read recommendations such as those that you cite, but they are intended for installations on hulls where the propeller is located upstream from the SONAR transducer, such as might occur on an inboard powered hull.

jimh posted 04-23-2006 10:40 AM ET (US)     Profile for jimh  Send Email to jimh     
The topic of SONAR transducer installation is covered in this REFERENCE article:

SONAR Transducers

"This article is a comprehensive explanation of SONAR transducer operation and installation with special emphasis on their use with Boston Whaler boats."

The article also provides an index to further resources on transducer installation.

jimh posted 04-23-2006 10:42 AM ET (US)     Profile for jimh  Send Email to jimh     
The topic of the cable path is also covered in the above article. See the section with the sub-heading Cable Path.
rumrunner posted 04-23-2006 11:23 AM ET (US)     Profile for rumrunner  Send Email to rumrunner     
Good point, mine is an outboard application and ahead of the prop, and as you point out, cavitation should not be an issue in that application.
highanddry posted 04-23-2006 01:56 PM ET (US)     Profile for highanddry  Send Email to highanddry     
I just read a similar recommendation to place it on the LH side. This, it was explained, was because propeller torque would tend to push that side down and lift the other--ok--whatever---what if youn have trimtabs which the Nantucket/Outrage really does need? In any case I don't think it matters as long as it has good contact with the water, clears your swim platforms, paddle wheels, trim tabs and all that stuff. J
Kencvit posted 04-24-2006 09:22 PM ET (US)     Profile for Kencvit  Send Email to Kencvit     
The Navman 4380 paddlewheel transducer on my 190 was installed by the dealer on the starboard side over the motor well. It`s located on the flat portion of the lower strake. The Navman manual recommends this general location, but also says to stay away from strakes,hull projections,etc. I`ve also read in the reference articles here to stay away from these locations.
First season everything seemed to work well so maybe while not ideal it still works. I would hate to move it now, there are 4 screws holding it!
I'm going to add a GPS unit that has a transducer and I am thinking of locating it on the starboard side again but over to the right further to be between the lower and upper strake. I would bundle the two cables together to near the bottom of the transom to reduce the additional number of holes for cable supports. Is this OK? How close together can two transducers be?
Thanks, Ken
bsmotril posted 04-24-2006 10:57 PM ET (US)     Profile for bsmotril  Send Email to bsmotril     
Back when Raymarine was Raytheon, their instructions said the transducer should be mounted on the staroard side at least 12 inches from the outer edge of the circle of the propellor's rotation. Their reasoning was the transducer would be less likely to pick up shockwaves and acoustical noise from the prop blades if they were moving down and away from the face of the transducer. This was on a dual 50/200khz unit. BillS
Livingwater posted 05-08-2006 02:14 PM ET (US)     Profile for Livingwater  Send Email to Livingwater     
We mounted the sonar transducer on the starboard side of the transom and it worked flawlessly on our first trip out on the water. No further adjustments were required.
jimh posted 05-08-2006 08:14 PM ET (US)     Profile for jimh  Send Email to jimh     
Ken--What sort of transducer does a Geo-Positioning Satellite receiver use that is immersed in water? Can you explain?

Most GPS receivers are designed to receive signals in the 2,000-MHz region. Most SONAR devices work in the 0.2-MHz region. These signal bands are in a ratio of 10,000:1 and generally do not cause mutual interference.

Kencvit posted 05-13-2006 01:21 AM ET (US)     Profile for Kencvit  Send Email to Kencvit     
Jimh, meant to say GPS/sounder combination unit. I`m looking at the Garmin 198C , not much more expensive than the 192c(GPS only). That would give me a back up sounder if one of my units went down. Also, it would give me the option to switch the Navman screens to show the Smartcraft guages only.
So in my question they would both be sonar transducers.
Thanks, Ken
jimh posted 05-13-2006 04:53 PM ET (US)     Profile for jimh  Send Email to jimh     
I have seen many fishing boats with dual SONAR's. I don't have any real-world experience with using two SONAR's at once. I am sure it would not be a problem if the frequency of the transducers being used were kept separate. For example, 50-kHz and 200-kHz transducer should not interfere with each other. My suspicion is that using two transducers of the same frequency at the same time might cause some mutual interference.

Perhaps someone who is an avid fisherman can help with this question.

If one of the SONAR units is a modern Raymarine digital unit, it may work better. These modern digital units are very frequency selective and tend to zero in on the precise frequency of their transducer pings.

Also, if two SONAR's are in use simultaneously, it will probably be necessary to separate the transducer locations. You won't want to have them mounted next to each other on the transom, particularly if they are at all close in frequency.

Kencvit posted 05-13-2006 05:22 PM ET (US)     Profile for Kencvit  Send Email to Kencvit     
Jimh, thanks for your reply.

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