Transom Mounted Transducer on Twin Inboards

[Norloch2]

Anyone have experience installing a transom mounted transducer to a twin inboard engine setup?  Most of what I've been able to find on line says you can do it as long as you keep the T/D as close to the centerline as possible with counter-rotating props.  Most manufacturers say they don't recommend it and do it at your own risk.

 

The boat is an '89 Princess 35 flybridge.  Twin volvo diesels.  The sounder is a Garmin 721xs and the T/D is a Garmin GT-20TM unit.  My typical cruiser speed is between 8 and 15 knots.

 

Thanks for any help/experience forum-users might have.

[Jori]

Why not use a regular solid bronze hull through transducer? Then you can place in front of the props and problem solved. With your (US) prices on Ebay, you will find a good priced there. I did this last season when I changed out my old one.

 

It's not an anser to your question, however I believe it will be the best sollution for your type of boat. Mine is pretty similar Princess Riviera 346/366.

 

And welcome to us in Norway, nice with some international participants here .  

 

May I ask what part of Canada you're frome? (Taken from your other thread) I have for a decade ago worked a lot in the Quebec area.

[Norloch2]

Thanks for the reply!

 

I agree that a thru hull is another way to go here... but the price difference between transom mount and through hull is crazy (like 450% increase). Besides that, I've already got a number of through hulls in the boat and would rather not add another with another fairing block, etc.  Further complicating my situation is the fact that the boat gets stored on a trailer for each winter - and I'm always worried about tearing one of those thru-hull fairing blocks off as I load it.  I've also considered an in-hull T/D, but I can't get Garmin's famous Down Vu technology with an in-hull T/D.  

 

Where in Canada?? I'm WAY up north in Yellowknife, NWT on the shores of Great Slave Lake.  The lake is the 10th largest in the world and the deepest in North America.  Minimum services but maximum privacy, wildlife and open spaces.  Drop these coordinates into google earth to get an idea of where I'm located.... 62 27' 14.68" N 114 22' 18.10" W.

[Jori]

May I propose you remove one of the old tranducer and use that hull instead? I did it with a bronze round transducer. (you also get them in plastic to the half price) It will assemble flush with the bottom (so no storage problems), and you can measure depth and degrees with it. I needed to wide out the excisitg hull a little bit, but easy, clean and fast job to do. (if anything with boat is fast) I also store my boat on land. In my part of Norway, we still have over one meter with snow and minus degrees.

 

The boat will have a good life in fresh water I understand. Much better condition compared with us that use the boats in salt water, and much better for the engines. Perhaps you can avoid typical challenges like the oil cooler or heat exchanger get stuffed. Typical issue for all VP 40 and upwards.going in salt water.

 

I notice it almost as faraway frome Quebec that you can be in Canada. The lake named after an Indian tribune? Nice with some history

[HerJo]

Hi Norloch2, and yet again welcome to the forum!

I bought a Garmin Echo 551dv (last autumn) with a transom transducer included. To avoid taking the boat ashore for installation I installed it next to the engine inside a in-hull tank I made of fiberglass and filled with non-toxic propylene glycol. This installation method will of course reduce the signals to a certain extent, and will not be a success if the hull isn't solid fiberglass. Anyway, you should weigh the pro's against the con's... It's working fine for me, but then again I'm not an "sonar pro".   

The tank is open in the bottom and shaped to the hull to avoid to "shoot" through more fiberglass than necessary.  I made a see-through removable cover as well. The tank is glued to the hull with Tec7 (if not available in Canada, I'm sure you have a similar multi-bond product). The location of the tank was chosen after trying and failing with the transducer inside a plastic bag filled with water...

 

The tank seen from the top.

Redigert 8.Mars.2016 av HerJo (see edit history)

[Kenneth 81]

Why not use a regular solid bronze hull through transducer? Then you can place in front of the props and problem solved. With your (US) prices on Ebay, you will find a good priced there. I did this last season when I changed out my old one.

 

 

Theres absolutely no reason to use a bronze transducer on a fibreglass boat. The plastic trough-hull transducers have the internal components as the bronze ones, so there no performance difference to speak of. (Years and years ago it was probably a different story, but thats then not now) Bronze transducers are intended for wooden hulls where the movements and flex of the hull can overstrain and damage a plastic transducer.

[Norloch2]

As mentioned earlier, I'm really not interested in using a thru-hull T/D for a number of reasons:

- 4.5 times the price

- if I go with something other than garim's very expensive thru-hull, I give up some of its functionality (Down Vu) in the head unit

- boat is trailered annually so damaging the (expensive) T/D is a real possibility

 

What I'm wondering is if anyone has tried a transom mounted T/D with twin inboards, what their experience was, mounting location, etc.

 

Thx.

[Norloch2]

Ok the purchase has been made.... I ended up going with the transom mounted T/D. Here is my logic....

 

- I've heard enough from various sources that this T/D, mounted in the centre of the two props, should work reasonably well

- the above is further supported by the fact that we typically cruise at low speeds (b/w 8-15 knots)

- if it doesn't work as well as I'd hope, I can try the approach put forward by Herjo and mount it in a liquid bath and have it shoot through the hull (I'll lose Down Vu functionality though)

- if all else fails, I can pull it from the large boat at the end of the season and install it on my tender. Then I can move the head unit from the large boat to the tender and explore new areas. If garmin's new map drawing application works as advertised, this set up will not only allow me to explore, but map otherwise poorly mapped areas while exploring.

 

Will post updates on how well this does (or dies nor) work.

 

Evan

[Kenneth 81]

That sounds like a very good plan to me. Hope it works well mounted on the transom.

[HerJo]

[snip..]

- if it doesn't work as well as I'd hope, I can try the approach put forward by Herjo and mount it in a liquid bath and have it shoot through the hull (I'll lose Down Vu functionality though)

[/snip..]

 

Loose DV functionality? That's news to me. As far as I can tell DV works perfectly on my Garmin as far as I can tell, but then again it might have been even better if the transducer was installed the way it is actually designed to be installed. Is this DV functionality loss your own experience or...? 

[Norloch2]

Hello again.  Garmin advised me that if I try to have the t/d shoot though the hull that I'll lose Down Vu functionality... I guess I just assumed they knew what they were talking about.  

 

Your set-up works reasonably well and you maintain Down Vu when shooting thru the hull??

 

What t/d are you using and what's the frequency (if you know)?  What sort of performance (depth etc.) do you get from your setup?  

 

This is good news... if it works, it'll solve my problem!!

[Norloch2]

By the way, the T/D I've purchased is Garmin's GT20-TM unit.  Here is a link to the specs if your interested..... 

 

https://buy.garmin.com/en-US/US/on-the-water/transducers/garmin-gt20-tm-transom-mount-downvu-500-w-chirp-455-800-khz-traditional-500-w-77-200-khz-transducer-with-temp-8-pin-/prod540580.html

 

Evan

[HerJo]

I'm at work in the North sea right now, and i can't remember exactly the T/D model nor the max. depth right here and now. However, the T/D was bundeled with the 551dv unit and hence probably a relatively cheap T/D.The specs listed in the webshop I bought it from says it's a 500W 4-pin T/D with 77/200 kHz & DownVü. 
 
As for the DV function I get "the same" picture as below with my installation method (as mentioned: it may be even better with design installation - I don't really know), and it was actually the guy in the shop that suggested to install it that way when i mentioned that i wasn't that keen on landing the boat just to install the T/D where it's designed to be installed. With regard to depht, I'm quite sure that I've had at least 150m (seawater) - probably more, but I have to check the log to be sure.
 
I tested the T/D (mounted on a stick outside the boat...) directly in the water as well as in a plastic bag filled with water in-hull (shallow sea water - approx 50m) before I chose the in-hull installation. I couldn't really tell the difference with regard to the screen output. That, and the simple fact that the T/D cable was to short to reach to my steering console, made the decission rather easy;  in-hull in a tank.
 
 

[Norloch2]

Thanks for the update.... I think I'll follow your lead and try to shoot thru the hull first.

 

Stay safe, and warm, working on the North Sea.

[Norloch2]

Quick update on this..... I cleaned off a section of the hull in the engine compartment, sanded it down to bare fiberglass and added about 1/2 a tube of 100% marine silicone. Then I just gently placed the T/D into the wet silicone, being careful about air bubbles, and let it set up.

 

The unit has worked perfectly since then..... And I put almost 100 hours on last year.

 

Evan

[reheat]

Hi,

 

I know this thread has gotten a little old but if you are still around... Are things still working out for you with the mount? Also, how is it in low depth say under 5'? I'm thinking of going the same route.