Mounting Transducers, Do Thru Hull Transducers Work? Mounting Transducers, Do Thru Hull Transducers Work?
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    Mounting Transducers, Do Thru Hull Transducers Work?
from Ken (  
4/27/2000 11:49:00 PM


 Well I have a bayliner runabout and I'm a bit weiry about drilling holes in my hull to mount a transducer. I've seen ads for "Thru-Hull" transducers, do these work? Is there any drilling required?

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   Names from Thom  4/28/2000 8:35:00 AM
 If you go back in the archives of this board or vist other boards you'll find that the use of the term thru-hull seems to mean different things to different folks. Let' get it right here. There are true thru-hull transducers and these have their face in contact with the water and require you to put a hole in your boat for their mounting stem. Then there are transom mount transducers and they too have their face in direct contact with the water. There are also shoot thru the hull transducers. These have their face in contact with some medium other than the water and the sound they produce has to pass through the hull of the boat. Often transducers intended for true thru-hull or for transom mounting are pressed into service as shoot thru the hull service. In order of efficiency from the most efficient to the least its goes like this 1. True thru-hull; 2. transom mount; 3. shoot thru the hull.

As a personal note it has never made sense to me for a person to spend a great deal of time finding out which is the very best bottom machine they can get for their hard earned bucks and then laying out a sizeable sum of cash, and often quite a sizeable sum indeed, for the best they could find only to couple it to the least efficient transducer type they could use.

There are certainly other considerations to the transudcer sort a person picks out. Folks that operate in very shallow water or water with many obstructions (flats and bass boats mostly) have good reason not to want something sticking out from the bottom of their hull. No question about that one. Another thing that there is simply no question about is that it takes more time and care to mount a true thru-hull correctly. Its is absolutly unquestionalbe that you really want to get it right the first time on a true thru-hull too. There are very good reasons you see so many transom mounted transducers; anyone can do it, the transducers themselves are the least expensive, they aren't much prone to water born damage from strikes. On the other hand they are easily hit by non-water stuff, the often suffer from turbulence at the back of the hull and so don't work correctly at speed, and of course the usual mounting schemes have you breeching the integrity of the transome with the mounting screws and that is eventualy going to lead to water in the coreing - the death of many a good boat. As to the shoot thru the hull mounting you get the trade off of loosing acoustic quality but gaining mounting ease. Basically you're just glueing it down and that's the height of simplicity. Some folks will contain the things in some liquid or another to give intimate contact and I guess that is a good thing to do but the process is basically the same. Aside from loosing power and sensitivity when using this mounting method you also loose, if the transucer being used has it - and all expensive one do - any speed or temperature reading capability the thing had.

Hope this helps ....


   My Experience with Shoot Thru from saul (  4/28/2000 10:14:00 AM
 I agree with everything Thom says. I decided to mount a shoot-thru on my last boat five years ago for most of the reasons Thom mentioned. I wanted to avoid physical damage, more holes in the transom, etc.

Before epoxying the tranducer in place, I tested it with a weighted rope to 25'. The depth range I fish in is 5'-50'. The unit read acurately (a H'bird Wide Eye, definitely not an expensive unit). I also had no bottom loss at high speeds, but that may depend on the boat. I was happy with the result. An effective shoot-thru installation will depend on keel contruction, so a test is essential.


   Word from Garmin from CKnick (  4/30/2000 4:44:00 PM
 I recently called Garmin tech support with this very question. I have a GPSMap 235 and due to hull configuration can't use a transom mount and don't like the idea of drilling a hole in the bottom. I was told if I use the Garmin plastic 200/50 KHz thru-hull mount and epoxy it to the inside of my hull. I would experience approximately a 1 to 3 percent loss of signal. Based on a guess that there would be approximately 2 inches solid fiberglass in the bottom of my boat. (It may actually be more or less I don't know, it's solid when thumped is all I can say, and the transom which is solid fiberglass is roughly 2 to 3 inches thick.)

Make sure you have a solid fiberglass hull if it's cored with wood or foam it won't work. To my way of thinking a 1 to 3 percent signal loss doesn't seem too bad, but I'm still debating on it and may decide to drill a hole in my 1 year old boat anyway. The transom mount just gets too much air and turbulance at planing speed.


   Might Want to Check That from Thom  4/30/2000 5:56:00 PM
 I suspect that you may have misunderstood what he told you. I would guess, simply because Garmin is a company I wouldn't expect to get garbage information from, that what he told you was that you'd experience a 1 to 3 decibell loss rather than a 1% to 3% losss. There is quite a bit of difference.

As to your hull's thickness I think that unless it has Buddy Davis' name on it somewhere you're looking at something a lot closer to a half to three quarters of an inch on the bottom and maybe 3/8" on the sides of the hull. If its a Bayliner or something similar just divide those numbers by 2 and it should give you a good idea of how thick it actually is.


   shoot thru the hull from sonars (  4/30/2000 6:15:00 PM
 Tests that we have done here at Genetron Technologies have shown a significant percentage loss of your acoustic window when you shoot thru any type of material.If your goal is to "see" fish be forewarned that you will be defeating the purpose for which you want to use the sonar
   ducers from nightides (  4/30/2000 10:19:00 PM
 I have been told that the signal loss of in a shoot-thru- the-hull application would be approximately 15%-20%.

It is almost as though you are insulating the responsiveness of your sensitive electronic sonar equipment. that in my opinion is not something that I would want to do especially if I intend on locating fish.

Stick with the transom mount.I have two fish finders with each of their respective ducers mounted on my transom. My results are consistent, reliable, and most of all, not restricted by the need to shoot-thru- my hull.

Just my opinion.

   Thru Hulls from CKnick (  4/30/2000 10:27:00 PM
 Thom, I really don't know (yet) what my hull thickness is, haven't drilled it yet. You're probably correct even 1 inch seems mighty thick for fiberglass. No it's not a Bayliner.

As for the loss when I spoke with Garmin I am pretty certain he did say 1 to 3 percent, but maybe I had the new guy or I did misunderstand what he meant. As I said I'm still debating whether I want to drill a hole. I know lots of people do it and I'm in salt water with few obstructions (logs etc.) but the general idea of a hole below the water line just plain worries me. Most of my fishing is in Delaware Bay where it's fairly shallow so I'll probably try to shoot thru the hull first. If I don't like the performance then I'll drill. Thanks for the input.


   why not try this? from reelmadnezz (  5/1/2000 6:41:00 AM
 take a small piece of wood, teak, pine, whatever, anything but plywood and epoxy it to the back of the transom. then mount the transducer to that. you won't have holes in the core of the transom and after the epoxy cures you will never get it off unless you want to. and a heat gun will work to soften it at that stage. good luck.
   Hull Configuration from CKnick (  5/1/2000 9:32:00 AM
 The problem for me is, I have a stepped hull design. Any where I mount it on the transom it will get air under it and won't work when on plane. I know, the dealer tried it last year in multiple locations on the transom. I finally called the manufacturer and was told to use a shoot thru the hull or a thru hull type.

I've dropped the transducer over the side and then held it against the hull inside (with a little water in the bilge to keep air out from under it) and did not see any difference on the screen. Course I was anchored at the time. I know from discussions with the manufacturer that the transducer must be in front of the step to work on plane, just not too far in front or it'll be out of the water when on plane.

Seems the more people I hear this from the more different answers I get. The boat manufacturer said they use shoot through the hull all the time and they work fine. I've had some people tell me this is BS and others say they've done it also and it worked fine. I've got the epoxy so I'll find out this next weekend if the weather co-operates.




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