Depth Sounders - Transom Mount or Thru Hull Sender?

[Boatman]

I'd like to install a depth sounder/gauge in my Classic 16 and understand I need to choose between a "transom mounted" sender and a "thru hull" sender.

Anyone with any practical experience to lend? Accuracy, especially once on plane is my key concern.

Thanks for any help. Brad.

[marcdups]

Brad, I installed a Lowrance 3500 with thru hull transducer, mounted the transducer on the starboard side under the engine and have yet to have a problem at any speeds unless you not in the water at the time, prep work is the key, sand the puck, make sure you have a puck, and also the area where you will install, It is not the easiest thing to do in the sixteen while you are on your head, and make certain you do not have any air pockets in the epoxy, and you will be OK, transom mount transducers account for more holes in the boat and can get snagged, do not like em!!

My .02 cents, hope it helps wink

[Ranman]

There was an earlier thread on this subject with lots of good info. Click the Search link, do a search for "depth finder" and see what comes back.

[FASTEDDIE]

Brad,
I have had both types in my boats over the years and thru the hull is the only way to go. It reads depth when the boat is at full speed and the outer transom unit may not and usually doesn't. The outer mount requires a PERFECT installation so that the water flows under your hull pefectly in a straight line then under your tranducer but if your mount is a hair off up or down from a perfect installation, water flow is interrupted and air bubbles will occur under the transducer and transducers can't read thru bubbles. You then must pull back on the throttle and stop to get any readings. By the time you stop to get a reading, you may lose a prop or clip your outdrive and be in shallow water. The black puck is held in a stainless steel set of brackets with sliding slotted holes with two screws to move them up or down in case you don't mount them perfectly flush , you then can adjust them. You then are instructed to put silicone in any gap between the transducer and boat hull to prevent bubbles or water shooting up straight like a rooster tail behind the boat. What happens is the screws loosen and it drops down or you bump the transducer putting it on and off the trailer or hit a floating twig or get weeds caught on it. The silicone drops out and bingo, it's a nightmare. Go for the thru the hull but the secret is before you permanently place the puck in epoxy, place the puck in a couple of different spots in the far rear of the engine compartment (thru solid fiberglass with no air in between the hull) holding it down with duct tape to see where the best reading occur. Once you put the a and b epoxy to it there is no moving it to a better spot. If you want to talk to transducer experts, talk to any guy with a Ranger Bass boat. The new boats have 3 transducers on them. :D :D

[RPD]

ditto on the thru hull comments... I have one on my sailboat and it's worked perfectly for years... plus, a tansom mount would be ugly on your 16, I certainly wouldn't put one on my 16OB... also, before you trust it too much at speed, remember what I guy told me about mine on my sailboat.... "a depth sounder usually tells you that you just ran aground"...

[pmreed]

Years ago I was looking for a way to hull-mount a transducer without punching a hole in the hull. I found a way! I took a plastic bowl that would fit flush against the hull in the engine compartment. I then mounted the transducer to the bottom of the bowl ( which when inverted becomes the top) angled so that it aims straight down after hull mounting, drilled another hole in the bottom of the bowl to fit a plug and then siliconed the bowl down to the hull. Fill with water (or mineral oil as I used), plug the fill hole and you're off to the races without a through-hull hole.

I had read about this procedure in some boating magazine back in the '70s, but I can't remember which one. All I can say is that it worked perfectly. Just be sure to mount it far enough towards the stern so that it's over the planing "contact patch". I used this on a 20' Reinell I used off-shore as a fishing boat. Read depth and bottom contour perfectly at 40+ mph.

[RPD]

Mounting the transducer in a small tank (glassed in pvc pipe worked well) of mineral oil inside the hull was an old trick to avoid cutting a hole in the bottom.... most depthsounders today have puck transducers that can simply be epoxied to the bottom... just check the instructions.... either way, there must be no voids in the glass or the epoxy used in the installation.

[CDMA]

Thru hull - At 90+ mph Geoo's still worked..nuff said.... :D :D :D

Chris

[Digger]

any opinions on what type of epoxy to be used? I have a Lowrance unit w/ thru hull sender. It has come unfastened from the hull, looks like someone used plain old caulk to "fasten" it in the first place. I'm thinking a true epoxy would be better than polysulfide or polyurethane sealant...

[pmreed]

My bad guys, you can see how long it's been since I installed a depth sounder/recorder. I was talking to Madpoodle yesterday morning over breakfast at Mt. Dora and got educated into the new century. Ain't it great how technology just keeps truckin' along. Transducers that you can run dry, what'll they think of next? Phil

[BigGrizzly]

Thne epoxied in my criterion has been there for at least since new at least 20 years.
Hey Reed ever get a Donzi?

Randy

[David Ochs]

This is a dumb question I'm sure. Doesn't the transducer have to be mounted somewhat parallel to the waterline?

[marcdups]

Digger, use some 3M 4200 will set in 24 hrs, and still removeable unless you never want it to come out use 3M 5200 but will take 7 days to set!!
either way I thing they are the best for your application.

You have not been anywhere if you have not ran aground eek! eek! eek!

[GEOO]

I used a plastic transom mount transducer and caulked into the bilge. The depth sounder manufactures say to use epoxy. I used a plastic safe, water proof caulk. A lot of the caulks will attack plastic. (read the directions). The trick is not to get air bubbles in the caulk under the transducer. Clean the inside of the hull with a good cleaner to get rid of any oil. Put a good amount of caulk down and push the transducer in. Make sur you mount the transduce in an area were it shoots only through the glass. ( not above a running strake or plywood core ). GEOO

[marcdups]

Geoo thought Digger had a thru hull transducer, which goes thru the boat instead of a puck which shoots thru the hull, epoxy would be too brittle in this application and does not adhere as well to plastics, I stand corrected.

[RickR]

Add some water to your bildge when looking for the best (PUCK TYPE) transducer location. In front of the engine a few inches off the keel has been a good location on my Classics.

I use regular epoxy (not the fast set), some companies call theirs "2 Ton". It has fewer bubbles and sets harder.

FYI
Clean and rough up the gel coat.
Do NOT use solvents on the puck.
Make a dam (so the epoxy doesn't run all over) out of plumbers putty. The putty can be removed after the epoxy has set.
Most of the time you can knock the transducer lose if it's in the wrong location with a slight rap from a chisle and hammer.
For a professional looking installation use wire loom and stainless adels on the transducer cable.

[CrackerJack]

I have a 16' classic and mounted the puck type
were RickR described. It works great and seems to
give an accurate reading. Compared it to Ted's this weekend. Mine is a Hummingbird model. Was
not very expensive. Jack

[pmreed]

No Randy, still no Donzi. Been kicking myself for not grabbing Ted's 18 last year :( . It was just what the doctor ordered. I didn't find out about it until it was gone...so...still lookin'.

Phil

[marcdups]

So is Ted still looking for it eek! eek! eek!

Hey Ted let's see that new avatar :D :D

[CrackerJack]

Marc,
Ted isn't looking for it.
I was able to hopefully capture the moment with
his camera. Jack :D