TomCat: Thru-hull vs. Transom Mount Transducer

M

Mike...

New member
Hi to everyone.

I have to decide between a thru-hull or a transom mount transducer.

My gut tells me never to drill a hole through the hull unless you absolutely have to. And even if you absolutely have to, don't do it anyway!

This seems like a case where I don't, but I thought I'd throw it out to the group.

Let me add that while we may someday fish a time or two form the boat, we will never be into fishing. So, I don't need to make this a big project.

What do you all think?
---
mike
 
I've got both Mike. A shoot thrugh the hull in the stbd hull for the Garmin and a transom mount on the port hull for the RayMarine. The RayMarine works better IMHO but they both do a good job. With my boat on a lift, the transom mount one doesn't get fouled but then, they make special antifouling paint for transducers.

Charlie
 
I have two transom mounts--one on each hull. There is (was?) a solid section of hull aft on the stb hull (most likely where Charlie put his Transducer).

Because I keep my boat on a lift and trailer it, I didn't want a thru hull. Shooting thru a hull is certainly possible and I have done it many times.

If you want one of the new high resolutino side scan units, you pretty much have to go with transom mount.

For the Transom mount, apply a piece of Starboard first. That way if you hav to move the transducer mount (or put in a new one) you are just screwing into the Starboard. You want to pre drill the 3 holes in the Starboard first--and then drill holes in the transom--over drill these, then fill with epoxy and drill the pilot holes. Yes, the Tom Cat has foam in the transom, but I still don't want water there. Freezing can cause probelms down the line.

There are also some flush mount transducers.

I hold the bottom well at 25 mph.
 
I'm of the mind set that I avoid drilling through the hull when at all possible.

I have a 600W Airmar Inhull (shoot thru) transducer and it works perfectly. I don't fish so I use it only for depth. I can keep bottom lock at all speeds. I have never found this to be the case with transom mount transducers.

If you wanted simple you could opt for the 600W, if you wanted performance you can get higher end units for hard core fishing. Our Tomcats are built with a dedicated Inhull transducer location toward the rear of the stb sponson.
 
One plus for the transom mount is that you can get a transducer with a speed sensing paddle wheel and a temperature sensor. Speed is fun to compare with COG to determine current.
 
matt_unique":2rexsyx3 said:
That link did not work for me, but it's the P79 model 600w 50/200 kHz.
Click to expand...
Ok it's this one here.

Hopefully, it the link will work this time. :)

Looks like it might be what I need; thanks Matt.

peterbrownell":2rexsyx3 said:
One plus for the transom mount is that you can get a transducer with a speed sensing paddle wheel and a temperature sensor.
Click to expand...
Peter, I do think that's interesting, but I prefer to not drill holes in the transom if I don't have to.
 
Before you install the transducer in hull, be sure to test the location, as shoot thru units won't work where there is coring in the hull.

Hang the transducer ocer the side of the boat in the water to get a baseline bottom image. Then put the transducer in a bag if water, and try it in various locations inside the hull. You should get the same image as when it was in the water.
 
The uncored spot on a TC255 is in the Stbd Hull, near where they have mounted the bilge pump. You can "see" it as a depression in the inside. Not sure if there is a matching one on the port side or not.

Charlie
 
Captains Cat":3jfo6s9e said:
The uncored spot on a TC255 is in the Stbd Hull, near where they have mounted the bilge pump. You can "see" it as a depression in the inside.
Click to expand...
How do you guys get down in there to work?
---
mike
 
wannaboat":252a8z3l said:
Captains Cat":252a8z3l said:
The uncored spot on a TC255 is in the Stbd Hull, near where they have mounted the bilge pump. You can "see" it as a depression in the inside.
Click to expand...
How do you guys get down in there to work?
---
mike
Click to expand...

Ha ha - wait for Charlie's response on this topic....

You need to prop your aft seat/battery hatch open for ambient light and of course reach in through the stb access hatches to get down there. It is a stretch, but with long enough arms (wear long sleeves to prevent scrapes - trust me) you can get it done. I installed my own.

1.) Find the spot. (Not easy to find the first time but once you find it you will wonder why it was hard to spot). Matt G's suggestion above is a great way to make sure you find the right spot.

2.) Clean hull surface with acetone - scuff with a little sand paper - and repeat with acetone.

3.) Set transducer housing to 14 degrees (I have to double check my log book housing to verify the exact number but I figured out the deadrise angle of our sponsons before I installed mine). It needs to be level.

4.) Forget the instructions that say to use silicone to secure the transducer housing - silicone is not strong enough - use good ol' 3M 4200.

5.) Fill housing with non-toxic antifreeze and insert transducer.


*I used a coat hanger to run the cable from the transducer to the helm station - there are enough areas where you can at least reach in behind the gunwales to grab the end of the coat hanger.
 
matt_unique":1gn1i5m3 said:
wannaboat":1gn1i5m3 said:
Captains Cat":1gn1i5m3 said:
The uncored spot on a TC255 is in the Stbd Hull, near where they have mounted the bilge pump. You can "see" it as a depression in the inside.
Click to expand...
How do you guys get down in there to work?
---
mike
Click to expand...

Ha ha - wait for Charlie's response on this topic....
Click to expand...

You need to do all those things except first, find a trained monkey with 4 foot long arms that knows how to handle tools and likes boats. :roll:

The newer TCs have larger hatch accesses and may be easier but my 2006 has the smaller ones. :crook

Charlie
 
You don't have to use a dedicated 'shoot thru the hull transducer)--any transom transducer can be used when "gluing it in place"--silicone (I have not had as good luck as with some other ways), epoxy, 4200 etc. I have also made a box which conforms to the configuration of the the hull. Glassed it inside and out, then set it in the hull with thickened epoxy. Fill the box with mineral oil (one of the best media for ultrasound transmission), and then screw on the top of the box, which is made level. A thru hull transducer can be mounted in this top. I also put a small garboard plug in the top, to replace or add mineral oil. Seems a bit more complicated, but this allows the use of any thru hull transducer in a "shoot thru the hull mode". I have used transducers in this mode down to 1200 feet (in boats which didn't go all that fast, but had very thick solid hulls (over 1.5" thick").
 
I have a transom mounted Raymarine. Works fine, except when there is lots of turbulence. I guess that would be true of any transducer.

But there is a second problem- barnacle growth. Now that really messes up the transducer. The special transducer paint DOES NOT WORK, at least in Texas. The barnacles here seem to look at it as a special treat...

Two years ago, in frustration, I just slapped on some Micron CSC on the transducer when I was touching up the bottom paint- and have done so a number of times since then. It adheres well, does not interfere with function, does not seem to have damaged the transducer housing in any way, and keeps the transducer relatively barnacle free.

Your mileage may vary...
 
The copper containing bottom paints caused more attentuation. Some of the newer paints are fine. I pulled by Caracal yesterday--9 months in the water, and a little slime on it, which pressure washed right off. I had the Petit Vivid on the transducer as well as the hull.
 
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