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Author Topic:   Thru The Hull Transducer On Classic Outrage 25
msl posted 05-28-2006 09:32 AM ET (US)   Profile for msl   Send Email to msl  
I have a 1983 OUTRAGE 25 with an open transom. My transom mounted transducer broke off the other day, and I'm in the process of deciding how to replace it. I did a search and have found that some say the OUTRAGE 25 has a spot where a thru-the-hull transducer can be mounted. Are there any pictures of a thru-the-hull transducer? Relate your first-hand experience in mounting a thru-the-hull trnsducer? If all else fails I will just go with a transom mounted transducer.
jimh posted 05-28-2006 01:00 PM ET (US)     Profile for jimh  Send Email to jimh     
It is not clear if you are asking about a transducer which is mounted on the exterior bottom of the hull and needs a large hole drilled into the boat bottom, or if you are asking about a transducer that is installed in a bilge space and directs its SONAR beam through the hull, without making any hole in the hull.

In general, with a boat that is used on a trailer, as most Boston Whaler boats are, you have to be careful about installing a transducer on the exterior hull bottom. Such a transducer could be damaged when loading the boat on the trailer, even if it is located in an area that normally does not contact any trailer supports. Boats often tend to skew quite a bit when loading on the trailer. Because most trailers have support right on the keel centerline or close to it, you would have to locate the transducer to avoid those supports.

Transducers which try to direct their sonic energy through the hull do not tend to work well at all with Boston Whaler boats because of the interior foam and the Unibond construction. In order for an in-hull transducer to work, the hull material has to be a reasonably good sound conductor and not have a lot of changes in its acoustic impedance. The acoustic impedances of foam and fiberglass resin laminate are quite different, and sound tends to be reflected from such a boundary. Even in areas of the hull which have been specifically manufactured without a foam filler (often called a "putty box" area), shoot-through transducer results have been poor.

Here is a prior discussion on this topic which may be useful:

Transducer Mounting Area

msl posted 05-28-2006 04:46 PM ET (US)     Profile for msl  Send Email to msl     
Sorry Jim, I'm not great with wording. I'm going to be replacing my depth finder/fishfinder transducer, which is currently located on the outside of the transom. A few friends of mine have recommended getting a thru the hull transducer(none are whaler owners), which would require drilling a 2" hole thru the flooring in the back two foot of the boat. I know there has been discussions on this before, but cannot find it.
oroseiwhaler posted 05-29-2006 04:41 PM ET (US)     Profile for oroseiwhaler    
i had on my '98 Outrage 23 the transducer first mounted tru-hull (drilling a 2" hole tru the hull) and after i've lost the pizo-cristal underway, i switched to a transom mounted transducer.
Also my buddy has the same deepsounder and the cheap transom mount (also called "skimmer")transducer and mine is inox tru-hull with PU fairing block mounted on a self made L-shaped mounting. There is almost no difference between both readings up to 1500 feet so the transom mounted skimmer transducers work quite well.
As Jim mentioned, tru-hull installation especialy of transducers is not a easy job on boston whalers due their thick foam core wich creates 2 problems:
1. bad results with in-hull or shoot-tru transducers
2. Tru hull transducers have to be mounted on the transducer mounting location due to the thick foam core wich is thicke than the stem of a normal tru-hull transducer.

Check Jim's article about Transducer Mounting Area and check on your boat if it has one.

Very good mounting instructions and a broad view of different transducers can be found on the site of AIRMAR, the leading transducer manufacturer for allmost all deepsounder brands.
The Instructions can be found here:


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