Mounting a Thru Hull transducer

[Murf'n'surf]

My comment was in response to @tdonoughue guessing the arrow might face forward.

Your hole's edge should be sealed with resin not embed the entire transducer in resin. Life caulk or 5200 will work splendidly for your hull to transducer adhesion.

Sorry that auto correct and my random babble confused you. lol.

 

[txav8r]

Sorry again @Murf'n'surf , so your saying to just paint the edge of the cut hole with epoxy or fiberglass resin, let cure, and then install the T/D, bedding the flange and side threads in a caulk? Life Caulk is comparable to 4200, a poly based waterproof caulk. 5200 is too rigid I think and if the T/D were to go out, would be harder to change, I'll use life caulk.

 

[Murf'n'surf]

You got it!

 

[utahrd]

I wonder if the factory mounted theirs incorrectly? Perhaps someone else on this forum with your boat can look under the hull and see which direction the arrow is pointing?

 

[Bruce]

The factory transducer is only for depth so mounting direction is likely to be less of an issue. Or they may want to measure the depth further forward and account for the angle in the display.

 

[txav8r]

Any angle other than straight down would alter the accuracy of depth. Why does my Yamaha thru hull T/D arrow point to the bow...it appears to be the same T/D that came with my Garmin 70S and...the stock T/D also measure temperature but I am betting it isn't, or function not used as a dual beam.

 

[Bruce]

Any angle other than straight down would alter the accuracy of depth. Why does my Yamaha thru hull T/D arrow point to the bow

Does the Yamaha display provide an accurate depth reading?

It would be easy to account for the dual angle correction in the software or hardware that displays the depth.

The instructions for the Airmar transducer state "From inside the hull, point the arrow on the top of the transducer (and the cable exit) toward the KEEL or centerline of the boat (see Figure 1). This will align the angle of the element inside the transducer with the deadrise angle of your hull."

 

[txav8r]

I don't have anything to compare the depth to yet. But it is much more reliable than the transom mount depth sounder was on the 230, and I assume the accuracy is good. I have read the instructions and fully understand them. The confusion comes from a "factory installed" Airmar transducer...with the arrow facing the bow, not the keel. lol, you guys keep telling and repeating the very directions I have here.

How would it be easy to account for inaccuracy during installation, if you don't know the error??? Nothing in the display system allows for you to enter corrections, known or otherwise. It might be easy for you to hack the yamaha system, but it would be easier for me just to install it correctly the first time.

This arrow corresponds to this arrow...

 

[Bruce]

How would it be easy to account for inaccuracy during installation, if you don't know the error??? Nothing in the display system allows for you to enter corrections, known or otherwise. It might be easy for you to hack the yamaha system, but it would be easier for me just to install it correctly the first time.

Yamaha may have chosen to use the angle to direct the sonar signal forward. If they did then they would need to correct for the dual angles (angle of the hull and provided by the sensor) in the software or hardware used to determine the depth.

Either that or Yamaha installed your transducer incorrectly which is why I asked if your depth reading is correct. If it is correct they are accounting for the angles. If it is not correct then it would be worthwhile to remove and correctly install the transducer to see if it improves the depth reading.

Although I have a bigger concern. Are your transducers operating on different frequencies? If not they are going to confuse each other. On bass boats they often use different frequencies between the transom and trolling motor mounted bow transducers.

 

[txav8r]

Your just full of good info aren't you? How many here have added chart plotters and other components with additional transducers to their boats? I have never read of anyone having a conflict with transducers, I guess there is always a first time. I think it is safe to say it is installed incorrectly, no way am I buying that Yamaha would deliberately buy a different angle and then go to the trouble to recalibrate for mounting. That is crazy. Now it is a possibility, that they don't care, and figure that accuracy of a transducer is not important, and just throw it in. Regardless, the arrow faces the bow in the stock T/D. The 70S has some ability to select frequency. But I don't know what the stock T/D frequency is. I suspect it won't be any issue but I will speak with Garmin regarding compatibility between two T/D's in close proximity.

 

[utahrd]

@txav8r ,

i bet the factory mounted it sideways. by trigonometry, if they are 10% angle wrong, only a 1.5% difference in depth reading, if 20% angle, 6.5% difference. imperceptible to you on depth readings. i say mount the arrow pointing toward your keel like instructions say. for a fish finder it matters more to be right on, since you are reading cones of arc around the boat. the dude at the factory who mounted the depthfinder didnt need to be right. 6.5 % tolerance good enough for him.

 

[tdonoughue]

Yes, despite my questions, you really can't argue with the directions. Which do seem pretty clear.

See? I told you I didn't know what I was doing...

 

[txav8r]

Yep, factory mounted it pointing to the bow. I talked with Airmar, maker of the transducer. They said manufacturers attempt to give you more forewarning of shallow water by doing this, and letting the transducer read forward of where it is actually mounted. But as noted by @utahrd , this reduces the accuracy by at least 6.5%. Airmar thought it might be a tad more than that, but that in most situations it shouldn't present any danger, and they didn't think remounting it would gain anything, considering I would be running a 70S chart plotter that will not only provide charted data, but show current sonar depth as well. Airmar also indicated that my chart plotter may indeed be able to adjust to either/or both frequencies that the P19 uses, but that it wouldn't be necessary since the DT820, the stock T/D, operates at 235KHz, and the P19, which I knew, operates at 77KHz and/or 200KHz. It is a dual beam, so if you use it as such, it will operate on both, otherwise, you would select a narrow or wider to suit your needs. I appreciate the discussion and finding out, but sometimes these things are better left out after the fact. In this case, I had not yet installed the P19, so it could have saved me doing it twice if it hadn't been compatible. I will update with pics.

I agree with you @tdonoughue , the directions were clear...why mother Yamaha would disregard them was unclear and confusing to me however.

 

[Murf'n'surf]

Sounds like we need to send a letter to the Yamaha factory!

 

[txav8r]

Here it is...

 

[Jim Robeson]

@txav8r ... Mel, just curious why you decided to go with a thru hull transducer as opposed to shooting through the hull. The reason I ask is that I'm considering the latter since the depth gauge I have now isn't worth a flip and I'm thinking of doing something different. Thanks.

 

[txav8r]

@Jim Robeson , I wanted both the temp and sonar. Some guys have reported that their in hull mounted T/D provided a temp. But no way that the accuracy of the temp would be correct in the bilge vs in the water outside the hull, IMO. I hate cycling through the pages of data on the gauges. The Garmin will give me much of what I always want to see, and I can keep things like gas gauge, and hours up on the main gauges.

 

[txav8r]

I spent a little quality time with my boat! I drilled that 2" hole in the bottom of her! And mounted the thru hull transducer. @Jim Robeson , I think I will be happier with the thru hull than a transom mount, especially since there is little place that is out of the way on the 240. I did as instructed by @Murf'n'surf , coated the edges of my hole with epoxy first. Then I sealed it with Life Caulk and tightened down the nut. I pointed the arrow at the keel, also as instructed. I ran the cable alone the other transducer cable and routed it out of the bilge, into the engine wall through the same opening, and into the starboard side compartment. I will clean all that up later. On a side note, I also cleaned all the caulk off of the clean out tray mounting lip, and intend to install my gasket mod that I wanted to do on the Nauti Dawg, and never did get done. That way, I can remove the tray anytime I need and not have to fool with caulk. Here are a few pics for the inhibited!
This is the 1/8" pilot hole drilled from inside the boat's bilge so I have perfect placement of my 2" hole saw guide bit.

Here is the hole as I cut it through from the bottom. Notice it is taped two directions (2 layers of blue painters tape). I ran my drill in reverse to cut through the gelcoat before cutting through the fiberglass, or at least I intended to...but it was cutting through in reverse so good, I just went all the way through like that. Took maybe a minute or less.

Pulling the transducer cable through...

And the finished install, I did clean it up just a little more after this.

I left my clamp on the flats on the housing to keep it from turning as I tightened the nut. That is tricky...what tool do you have that will open to 2" and hold that sucker?! I used a small C-clamp and it hit against the edge there and I just tightened the nut until I couldn't tighten any more. I will fill the interior hull with water and check for leaks.

I will also get a pic of the finished install without the c-clamp...

 

[txav8r]

They do a much better job of sealing up wire run holes they cut in the wooden stringers today than they did just 5 years ago!

 

[utahrd]

That looks great Mel!

p.s. I did the cleanout tray gasket mod last weekend. i had totally had it with removing 4200 (again). every time i remove the cleanout tray i say "thank goodness i wont have to do that again...." and then 3 months later another mod comes along.

p.s. what do you guys do for stripped screw holes, as is common in the cleanout tray?