Shoot thru hull transducer advice

[beancounter]

Well last week I went across the Chesapeake to fish and it was rough as a cob. Bottom line bad visibility and I ran into a net and broke the transducer bracket off my transom. Can't fix stupid!
Anyway thinking of cleaning up a bit and try mounting the transducer in a glob of silicone to shoot thru the hull bottom. Guessing some of you guys have done this and would appreciate all advice/warnings.

[Diablo]

When shooting through the hull you loose some of the transducers power so you may not see as deep as before. I have done it and it works. It wasn't on an Arima. You will have to mount the transducer on the actual hull not the liner or anything with foam.
Personally I would fix the transom mount and put it back there. What are the chances that will happen again. 

[davidsea]

   I'm using mine only as a sounder, not a fishfinder, so I can't comment on how a more sophisticated transducer would be affected.  In any case, the 'glob of silicone' method won't work well.  The bond between the face of the transducer and the hull needs to be as thin as possible, free of any trapped air bubbles, and using an epoxy that cures hard.  This minimizes the loss of energy from the transducer to the water.  Any silicone or polyurethane (5200 type) is too flexible, and will cause signal loss.  I used a simple round puck-style transducer bonded directly to the bottom, right beside the Arima factory bilge pump mounting pad.  Using a cheap ($90) Hawkeye digital sounder, I can generally hold bottom to at least 200' while underway, often more.

[FishAddict]

Just drill the hole and get a thru hull and be done with it.  Your a little far away otherwise I'd be happy to drill the giant hole for you

[croaker stroker]

Think of the transducer as a speaker.

+1 what Diablo said.

[beancounter]

Thanks guys I guess I need to find and order a new bracket. Not an emergency right now as the season closes here 12/31 for a bit and the water is still about 45 degrees. Not too cold for a ho hand for a spot check now and then.

[Yachter Yat]

    Bean;  DON'T DO IT!  Best place for the transducer is inside the boat.   I don't understand all this talk about lost resolution.  I've never had a problem in that respect.....at least in the max of a few hundred feet we're generally searching.  If your attempting to mark "extremely" deep with a shoot-through, then you would simply choose a transducer of sufficient power in order to overcome whatever loss you might anticipate.  When I say "extremely" deep, I'm thinking something like "four figures" deep.  Ha 

   Installing a shoot-through is a relatively simple job.  I mounted mine as far back in the bilge as I could reach; meaning, through the access panel in the floor hatch.  All you have to do is clean the area well.  I used alcohol, then lacquer thinner.  Cleaned several times, then lightly sanded and cleaned again.  BTW, I would advise against using straight silicone.  I used that once, and discovered it was permeated with tiny air bubbles.  Long story short:  Had to remove the ducer and start over; this time with LifeSeal.  Worked great! 

   So, get yourself a small tube of LifeSeal and cut the "tail end" squarely-off with scissors.  This will give you (for lack of better words) a "wide mouth" that will enable you to more easily spread the LifeSeal on the face of the transducer and lessen the potential for trapping air.   Now don't go thinking this is that crazy, but you may actually want to level the boat.  I did this only side-to-side across the sponsons.  (Had to let the air out of one tire, but it worked....Ha) 

   Okay?  Now, if you don't already have one, get yourself one of those small "torpedo levels".  With the hull cleaned and prepped, spread the LifeSeal over the face of the transducer. Do this in sort of a "sweeping motion", in order to avoid trapping that air I mentioned.  When putting the transducer in place, carefully set it down on a angle....again, so as to avoid trapping any air.   You know your boat is level, right?  So, simply level the ducer side-to-side.  Some may laugh at this, but if you happen to be radically off-angle on this......well, you can do the math at hundreds of feet down, right?   I've done a number of mine like this and never, ever had a problem.   As I've mentioned in the past, one of the beauties of using LifeSeal is:  Not only does it stick quite well, but it also has the benefit of allowing for easy removal without the potential of hull damage in the future.   For my money, there's almost no other way.  Unless, of course, you just happen to be absolutely crazy about "transom spaghetti".   


Yat

Edit:  BTW, we understand the transducer will be placed dead-center of the bottom, right? 

     

[beancounter]

Too late Yat ordered another plastic bracket a bit ago. Hey the screws are still there. Makes an easy install anyway.

[croaker stroker]

Everyone is entitled to an opinion.....but "resolution" loss is a fact.

[disposable]

Just drill the hole and get a thru hull and be done with it.  Your a little far away otherwise I'd be happy to drill the giant hole for you

when i had a similar problem, my replacement bracket was $21 shipped to my door. when i bought my most recent fancyish transom-mount ducer, it was $300. my next transducer will be a $1500 through-hull and presumably, that will also be the last.

[Barnaclebob]

In the kayak fishing community its very common to mount transducers in the hull using duct seal putty.  Ive mounted a transducer this way and it works great.  Given its a thinner plastic hull so a thicker fiberglass barrier might be different.

Duct seal isnt permanent but also wouldnt be fun to remove.  Could be something to try.  Depending on how rough the inner hull is, the duct seal may not get into any nooks and crannies.

[Yachter Yat]

      One of these fine days, someone is going to actually test the difference in resolution between transom mounted and shoot-through transducers.   Obviously, this test would have to be performed with 'identical' transducers, connected to 'identical' fish finders, on 'identical' boats.  (Whew!)    Sure, you could lie, and tell me you see a "big" difference........then I'd have to tell you to remove those "wine glasses" your wearing ahead of your eyes.    


Yat

[croaker stroker]

      One of these fine days, someone is going to actually test the difference in resolution between transom mounted and shoot-through transducers.   Obviously, this test would have to be performed with 'identical' transducers.... 


Yat

There are results on the Airmar website.

[Salmon Hobo]

I run 2 shoot through hull transducers...both originally made for transom mount. Both work fine. The Lowrance works fine to about 500 feet when trolling and works fine while running the boat up to about 30 miles and hour.  The Hummingbird is great for bottom when trolling and bait balls, fish etc..but loses bottom as soon as I pick up any speed. But with the combo it has been amazing for years of fishing and traveling through water I had no idea of the bottom depth. So seems like a win when I have never had to worry about bumping or knocking something or mounting on the transom. Both are mounted just inside and behind the bilge pump inside the fish holder tray access hole.  I am sure they would read better on transom but don't mind the small loss. I did have the hummingbird on an older boat before on the transom and it did pick up reading clear under speed...so I know that has been lost on that while travelling at speed for one of the 2.

[calcoast]

I run an Airmar M285HW shoot through hull transducer. It is fantastic. I hung it over the side one trip and then ran it inside one trip. Then installed it. I could not tell the difference on my Simrad evo3 unit. I fish in the salt up to 300 ft or so. I have no hesitation recommending this transducer for my type of fishing.

[croaker stroker]

You would probably loose less than 10%. You might not notice.

It is a trade off. Slight depth/sensitivity loss versus ease of installation.

My FF is only 600 watt. I can't afford any loss. A 1000 watt in-hull FF/transducer would outperform mine even loosing 10%.

[Yachter Yat]

   Airmar is based here in N.H.......just a few towns West of us.    I've actually been there on a number of occasions.  Got a bit of an education from some very nice people.   It was quite a number of years ago now, but in fact, this subject of signal loss is something that I asked about on one of my visits.  As I recall, the engineer I spoke with pretty much verified what calcoast just posted, with respect to the minimal level of signal loss with the through-hull installation of these transducers.  From what they tell me, much of it has to do with the relatively thin hulls of these smaller boats.  Additionally, minimizing the amount of sealant between the face of the transducer and hull also plays a fairly significant role in their performance.   

   Notwithstanding the above, if a through-hull installation, along with the highest possible resolution, is of paramount importance, then I'm sure a transducer with a bit more power would probably serve the need.  Personally, I'd never really have a need to know the eye color of the species I'm attempting to hook. Ha   But....if need be (without actually inquiring), I'm guessing Airmar might direct you to that M series as well. 


Yat   

[croaker stroker]

This chart shows an example of what you might loose...

Interesting, maybe due to wavelength?..... the most loss is in the thinner fiberglass. (3/8")


I agree with Davidsea,  a glob of flexible adhesive between the hull and transducer would increase the loss.

[Hunter]

To eliminate any further interference or loss of signal....... some installs use a housing system filled with liquid like antifreeze.   Here's a really good video of this type of install.   

https://www.youtube.com/watch?v=bMp_cmbdhYw&t=4s

[Yachter Yat]

     Mineral oil works well also.  Back in the 70's I used it to fill a short piece of 4" PVC that was glued to the hull, and housed my transducer for the installation in my 21 Stamas.  A boating buddy of mine did the same thing in his 20 foot Grady.  We were "crazy creative" back then.   


Yat 

[Hunter]

     Mineral oil works well also.  Back in the 70's I used it to fill a short piece of 4" PVC that was glued to the hull, and housed my transducer for the installation in my 21 Stamas.  A boating buddy of mine did the same thing in his 20 foot Grady.  We were "crazy creative" back then.   


Yat

I think that using pure antifreeze as the liquid medium is self explanatory.    Other liquids could freeze and create other issues....  For you California folks that never get a hard "freeze".... then other options might be just fine....   Maybe, Gray Goose Vodka or Petron Agave.       

[calcoast]

The Airmar M285HW comes with a housing that you fill with antifreeze. So the sounds shoots though the antifreeze and then the fiberglass. It is like an upside down plastic bowl/cup with the transducer on top. I tried several spots in the bilge in front of the bilge pump. They were all equally good so the fiberglass must be pretty solid in those areas.

[headduck]

The Airmar M285HW comes with a housing that you fill with antifreeze. So the sounds shoots though the antifreeze and then the fiberglass. It is like an upside down plastic bowl/cup with the transducer on top. I tried several spots in the bilge in front of the bilge pump. They were all equally good so the fiberglass must be pretty solid in those areas.

I like this...new to me...always assume transom mounted was the way...

I have been dreaming of 2 transducers (tm185 and SS3D)  plus trim tabs (eventually) and there is just not enough space. I also get some interference/shadowing with the main. Also less transom spaghetti as Yat suggested.

Thanks for the share.

More info re:fiberglass signal distortion
https://www.thehulltruth.com/marine-electronics-forum/804755-airmar-m285hw.html

[straiteagle]

     Mineral oil works well also.  Back in the 70's I used it to fill a short piece of 4" PVC that was glued to the hull, and housed my transducer for the installation in my 21 Stamas.  A boating buddy of mine did the same thing in his 20 foot Grady.  We were "crazy creative" back then.   


Yat

I did the same originally on my 22SL, in 2006, with a transom style transducer- 4 inch diameter pipe, about 3" high, around the ducer mounted in silicone, then the pipe filled with mineral oil.
used this until 2018 when I bought a new Garmin 1040 GPS/FF with a universal puck style ducer, came with 4 different mounting bases/outer rings of varied degrees to match your hull slope, fasten to the bottom of a well cleaned hull with a special silicone as the plastic is made of a compound that does not adhere with the special type, then fill the inner with the recommended mineral oil, set in the puck and screwed it down to the mounting ring.  works great!  Still have the original 2006 ducer mounted and cable still run with the old Garmin FF held as a reserve, set in the rear....and still using the original Garmin GPS as dual system at the helm for when I want to use the 1040 on full screen as a FF.

[stinger]

I have this shoot thru the hull Airmar P79 for sale if anyone is interested. Bought it a few years ago and never installed it. $75.00 plus shipping