depth transducer

[howard armstrong]

I am getting ready to install an new dept sounder. The location on the transducer is going to be in the seat base,starboard side, just behind the vee birth bulkhead. the question is,do the oil bath transduces work as well as a thru the hull type. The tech support person says yes but i would rather have you guys oppinion.
Thanks.
Howard
Angelina

[Rodney]

In my experience, mounting a transducer through hull is always preferable over trying to do some sort of oil-bath (or other non-through hull) scheme. I'm not sure who your talking to, but if manufactures really thought that mounting the transducer inside the boat works as well as drilling a hole in your boat and poking a transducer through it, they certainly would exploit that and design all their transducers accordingly.

Back when I used to do Marine Electronics for a living, it was always explained to me that fiberglass had a significant dampening effect on the ultra-sonic sound waves generated by, and received by transducers. And in virtually in every case where we had customers who complained of poor sounder performance, it was because they tried to get away with mounting their transducers "inside" (and believe me, I've seen some pretty "voodoo electronics" like attempts do so).

As far as location, I would make sure that transducer is mounted reasonably aft. In a C34, that would mean keeping it out of the vee-berth area at least.

On my boat, some previous owner mounted the transducer under the vee-berth. I'd like to hunt him down and do some serious ear chewin'. It's too far forward and because of this, I get a fair amount of aeration over the surface of the transducer when the boat is only slightly heeled or even in very moderate sea state conditions. This aeration causes significant falsing of the sounder often putting me in 2 feet of water when I'm really in the middle of a channel with an Aircraft Carrier going by. Putting the transducer further back significantly reduces this problem.

Another advantage of putting the transducer further back is, because of hull shape, you can get the transducer to mount to a plane that is more parallel with the ocean bottom. Again, on my boat, because it's so far forward into the vee, the transducer is mounted at a fair angle, turning it into more of a danged sonar than a depth sounder. I'm exaggerating here a bit, but you get the idea, the more the transducer is mounted at an angle, the less accurate the "true bottom depth" reading will be.

Of course, too far back, and you'll start running into problem with the things that the prop is doing so you can take this too far.

Hope this helps.

[Roc]

I used to have a Precision 23 and I installed a Standard Ds40 (I think that was the model)depth sounder.  Standard told me they had three types of transducers. Aft mounted (like what is on power boats mounted on a bracket off the stern), another that is mounted in a hole in the figerglass, and (this is the one I installed) a transducer that shoots 'through' the fiberglass by being mounted inside the boat.  I installed this 'puck-looking' transducer by using marine tex to bond it to the hull.  Standard told me the only drawback by shooting through the hull is that you limit the maximum range from 250 ft. to about 150 ft.  The minimum range of 2.5 ft. stays the same.  I have to say that I had that depth sounder for 4 years and it never gave me false readings.  The shallow readings were not compromised.

To Rodney.  I don't know what type of depth sounder you have, but my Raytheon ST-60 (again, I think that's the model, or it may be ST-50) did exactly what you mention.  Saying I was in 2 feet of water when I actually was in 60 feet.   I called Raytheon and they told me that their program version was bad (I verified I had the version they mentioned, you do this by pressing a sequence on the buttons).  Anyway, they sent me a new head unit (transducer was good), I swapped it out on the pedestal and now everything works fine.  This happened after the unit was working correct, then it started giving me weird readings.  This was a new boat and all electronics came from the factory.  

About location, my C34 has both the knot wheel and depth transducer located under the v-berth, on either side of the centerline of the hull.  I understand that these units are mounted forward of the keel so not to be in the wake of the water passing from the keel which would affect the readings.  Also, the depth transducer is giving readings before your keel could hit the shallow water (granted it's only a few feet ahead and you would have to be going VERY slow to use that as an advantage).

Roc-

[dsavary]

I have a Navco instrument system in which the depth transducer is mounted inside with the tube fiberglassed on the inside of the hull.  the mounting location is the same were you intend to mount yours. I bought the boat new 1991, and had the same unit working all this time.
Why inside instead of through the hull?  An old salt once told me that the least amount of holes you can drill through the hull the better.  The mounting instructions gave me this option and I thought if it didn't work then I could always drill the hole.  Never had to. I check the fluid once every spring (castor oil) to make sure that it is full. Transducer must be in a liquid medium for it to work correctly. A previous member mentioned you loose maximum depth shooting through the hull. I can tell you I have been in water over 200 ft and never lost the signal. This is the best solution if you replace your unit, no hole has to be filled or re-drilled.  good luck!!! :cool:

[Rodney]

Typically, when I give advice to put a transducer through hull rather than inside, I'm usually greeted with a chorus of "mines been inside for years and I've never had any problems etc."

While I'm sure that is true, let's examine the context. First of all, the original poster explained that his advisor had suggested that mounting the transducer inside would "work as well" as mounting it through hull. That simply is not accurate. It will work, but simply not as well. Again, that is why you will ALWAYS see a through hole transducer installation in any demanding or professional depth sounder installation.

Also, there's more variables to depth sounding than just sending a signal out and calculating the return time from bottom. First of, often times simple digital readout sounders can be confused by which reflection it is receiving actually represents the bottom! There are many things that can confuse a sounder. Things like thermoclines, thick pools of fish, large plankton schools and other factors can often lead to a false reading. There isn't a one of you out there that hasn't been mystified by an odd reading occasionally by your sound because of these things. By sticking your transducer inside, you weaken the power your signal has to punch through some of the aquatic "murk" giving you the potential for more false reading than you would otherwise have. So it's not simply a depth issue you will be dealing with by sticking your transducer inside, but also the power for your transducer to work at it's best.

As a matter of fact, I used to be quite biased (and still am a little) about digital readout depth meters. I always felt the video readout units gave you more information about what you were looking at and certainly gave you a better idea of historical trends.