Through Hull -vs- Shoot Through

[Kenlahr]

Wow, this is a debate that lives on and on. Just when I though I had made a decision, Steve Bradburn at Furuno has managed to change my mind. Looks like I am going to put a hole in the boat and make a few modifications to my trailer bunks. Here is what Steve had to say:

Ken,
Thank you for your email.
As you probably know there are pros and cons to both in-hull and thru-hull transducers. I favor thru-hull transducers. There are two disadvantages with in-hull ducers. The first is the signal loss that happens when you shoot though the hull. The second is the bubble or turbulence layer that will pass over the face of the transducer when the vessel is moving. Granted there are success stories from folks who are using in-hull transducers but I have been on a lot more installations that haven't worked than have. Very rarely do you ever see a vessel that has both in-hull and thru-hull transducers but attached is a picture from a vessel I was on in Cabo. The thru-hull transducer was a 1Kw 50Khz and the in-hull was a 2Kw 28Khz. The 28Khz should have blown the socks off the 50Khz, especially in 100ft of water. But as you can see that was not the case. If you are spending most of your time fishing in depths of less than 1200ft I would recommend a Airmar B-260 with the high speed fairing block.

Kind regards,

I will post the picture later...

 

[Kenlahr]

Pictures

Here is the picture provided by Steve at Furuno. On the left is the through hull and on the right is the shoot through.

 

[gulfcart]

Just a note - my Furuno/ M260 - 50/200 1kw in hull @ 200khz has a much clearer and more detailed picture then when I use the 50khz freg. Looks like both of these examples are at low khz levels. Of course west coast Fl. I dont get in water much over 150'. The bottom detail is always great, just issues of where to install for high speed read outs.

 

[megabytes]

Be aware that the large, 1KW ducers can produce a bubble trail in the engine paths on some hulls depending on placement. I was told by several folks NOT to mount one on my 300 as such a bubble trial can rob the engine of proper cooling and also affect prop grip.

Although often panned on msg boards, I used the recommended 600w transom mount at the drain plug on my hull. I track the bottom at 30 kts and have excellent resolution. While I have read many reports of good 1000w in-hull performance, it should be noted that the signal loss can be anywhere from 20-30% depending on the hull thickness and composition.
Therefore a 1000w in-hull may only have an effective power of 700w. The larger ducers have more elements but again, some sensitivity is lost through the hull. Note I rarely fish depths over 500 ft so that is a factor as well.

I am not recommending a transom mount for everyone but the bad rep against them is simply urban myth. One of my recommendations came from a leading installer who is a tester for early Furuno products and widely considered one the best experts in the mid-Atlantic. I have been very pleased with my sounder performace and will likely repeat the setup down the road in my next boat unless some RELIABLE advice suggests otherwise.

FWIW

 

[TunaT]

transducer

Finally, someone that uses an transom mounted unit......Megabytes thx...I've always stuck with the 600w model for all my boats. I have a hard time drilling a large hole in the bottom of my boat.....I know its been done for years with NO issues....but call me old fashion if you must, transom mount for me. Megabytes, ever considered the 1kw model?? Airmar makes one but don't like the looks of it, with that foot long piece of pipe

 

[megabytes]

I may consider it for M3. :lol:

My last boat had the 600w thru hull. The transom mount works every bit as good and there is one less hole in the boat. From what I read it is really the additional elements which improve performance in the larger ducers, assuming you don't fish deep waters and need the additonal power. Most of our fishing is in 60 to 250 feet of water. I get excellent detail with the transom mount and it is in a place where the forklifts will not touch it.

I would likely be laughed off THT for even suggesting a transom mount but the proof is in the results. I also have a in-hull smart sensor for my RD30s. Interestingly, it will read depth when running through a bunch of wakes when the transom ducer cannot read. This is most helpful in our shallow creeks and waterways.

 

[beagleboy]

Megabyte, did you mount the transom mount transducer near the center drain plug? Mine is a 500watt mounted more to the outside but I lose pic at speed > 20mph unless I tilt transducer up a little bit> So is it better to mount transom mounted transd. more in center line of boat?

 

[jimmy's marine service]

i've lost count of the transom mounted 'ducers i've installed...NONE have lost their signal at speeds... :wink: it's all in the placment...

personally,on an outboard powered,i prefer a transom mounted 'ducer,due to the fact,the boat is usually trailered...trailering with a thru hull 'ducer is sometimes a problem...

i don't like the shoot thru the hull style 'ducers...no speed pick or temp pick up either....

 

[capt chris]

i've lost count of the transom mounted 'ducers i've installed...NONE have lost their signal at speeds... :wink: it's all in the placment...

personally,on an outboard powered,i prefer a transom mounted 'ducer,due to the fact,the boat is usually trailered...trailering with a thru hull 'ducer is sometimes a problem...

i don't like the shoot thru the hull style 'ducers...no speed pick or temp pick up either....

Jimmy,
Where would be your preferred location to mount a transom mounted 200 kHz on a new 2008 Tournament 225? Thanks

 

[megabytes]

Beagle,

Mine is right next to the drain plug. According the installer this is the best place on GW hulls for several reasons. There are strakes and other bottom features which will produce turbulance and cause the ducer to lose tracking. That is probably happening in your case.
Mine only loses the bottom in stirred water with recent boat wakes. The in-hull continues to track in that case.

I recall asking the installer if the ducer was in danger of being broken by the forklift. He laughed and said if it does then they have dropped your boat. :lol:

 

[Curmudgeon]

The second is the bubble or turbulence layer that will pass over the face of the transducer when the vessel is moving.

If the "bubble or turbulence layer" affects the in-hull, it will also affect a thru hull. Unless you fish in very deep water, turn up the gain some and fish away with an in-hull ... :?

[/i]

 

[beagleboy]

I have the 228g grady which is the bracket mounted outboard motor. Does transom mounting in centerline near drain plug pick up turbulance/air bubbles from prop?

 

[TunaT]

beagleboy........the answer is NO for most applications, going in reverse and going into a prop wash are the only way that I lose bottom. The transducer is mounted in front of the motors in bracket and non-bracket models...runs clean almost all the time. Put it in a hard reverse then I lose bottom for a few seconds, go in normal reverse and no effect.

 

[capt chris]

I have the 228g grady which is the bracket mounted outboard motor. Does transom mounting in centerline near drain plug pick up turbulance/air bubbles from prop?

Beagle Boy,
I called Grady White customer service and on my 2008 Tournament 225 their recommended location for a transom transducer is a minimum of 8 horizontal inches away from the centerline (Keel) between the raw water intakes and the trim tabs.
My 225 and your 228G are both Grady drives and the hulls are the same so I bet that would work for you too. You could call GW cust. service and confirm. Let me know what you end up doing and good luck!