Noise at plane speed

[Keta]

I have a tzt3 driving a thru-hull B275LHW transducer in a glass boat, 28' Farallon Walkaround. Works great at troll speed et cetera. IE I like it when all the gear is in the water and I'm fishing.

As I increase speed when in CHIRP mode it's like a bunch of gain is introduced into the picture. I can still track bottom even out to 100 fathom with no gapping but the unit is unuseable for finding fish at speed. Furuno USA came out to the boat, Eric was one of the guys and felt something was off with the install....great service. It works better dumping a bunch of gain, gain that I can use trolling/fishing and switching from CHIRP to CW but that's a pain in the ass and doesn't me much spotting fish or bait when on plane. Life took over for a bit so I neglected the troubleshooting path till now. Fishing season is getting close.

Yesterday I crawled under the boat to take a good look at the install. There is a "Slight" lip with the the transducer not being 100% flush with the fairing block. Fairing block extends slightly further down. You can also see some gapping between the transducer and the fairing block. Trailing edge has a bigger gap but the front has some gap also. Would this be enough to be causing my problems? Would it be worth trying to fill the gaps with some silicone sealant to try to smooth the waterflow?
Thanks,
Kim

 

[Deep Blue]

Keta,

Keep in mid that the best place for mounting any thru hull transducer is as close as possible to the centerline of the hull and towards the aft of the boat. Choosing an aft midship location ensures that the transducer will be in contact with water even when you are planning at high speed. So having a very flat surface to provide clean water flow over the face of the transducer is very important to the transducer's performance.

Transducers used on stepped hull vessels must be in front of the first step and low to the keel to operate properly. Any live well or cooling intakes as well as chines, steps and strakes can all introduce aerated water into the path of the transducer and will cause you turbulence. So, remember to always look forward all the way to the bow of the vessel to see if there will be any interference in front of the transducer’s mounting location.

While you may have a slight lip with your transducer and it's fairing block, this can cause bubbles along the face of the transducer. however, I do sense that you are getting some type of turbulence from one of the other items that I have listed above. :think

- Deep Blue

 

[Keta]

Thanks for the reply Deep Blue,
Here's some more picture of the bottom
This is looking forward. Aft of the transducer by about 18" is a seawater intake. I wouldn't think this would cause a problem since it's aft. On the right side of the trailer bunk there is an inner chine and then it goes on out to the main chine....smooth or no step downs forward.


Looking from the bow to the stern. You gotta look hard but you can see the ducer.


Engine compartment. Inboard side is against an engine stringer. It might be possible to move inboard and a bit forward close to the bilge pump but it'd be tight with the engine and also trailer bunks. It's doable I think. Would this be worth a try?? I'd need to find a glass guy to patch the holes if I do move.



Or...would it be better to wait because of lead time and get a pocket mount combo with the dff3d elements in it? Mount it as close as possible to the bilge pump?

 

[Deep Blue]

Keta,

Thanks for providing the pictures of your transducer installation, these are helpful. After looking through all the pictures, I don't see anything that would cause of the turbulence that you have described.

Would it be possible to take series of pictures of the TZT3 Fish Finder screen showing this "gain" while slowly increasing the boat's speed.? :think

- Deep Blue

 

[Keta]

Will do. I more than likely will launch tomorrow so will run try to get some shots then. Actually last summer Eric Kunz & John Kourn came out to look at the boat and go for a spin. He felt hull noise was the problem or that was the impression I got from him. I got busy with other things so kind of put the problem on a back burner till now. I was wondering about the installation thus putting these pictures up. Before Eric looked at it I worked with via email Jon C.. He kind of felt it was a radiated noise of some sort. One of the things we did was install a large capacitor which didn't do much if anything. You can see the cap in the engine room picture. Transducer is right under the alternator.

I'll try to get you some updated pictures in the next day or two.

 

[rodneymeyers]

I have a 26' panga. While talking to airmar on a 1kw transducer for my boat they did not recommend using a transducer with a fairing block on a boat under 30'. He did not give and exact answer of why, but said they do not seem to perform the best. I have a flat spot in the back and had a box made and my transducer is counter sunk flush with the bottom of my haul. I works great. Maybe call airmar.

 

[Quitsa]

From my experience, on a boat that size with that hull shape you are fighting a losing battle especially with a fairing block. There will be a "speed limit" above which there will be enough air introduced and enough disturbance of the flow that the sounder picture will be noisy if the gain is high enough to show fish. I don't think your experience is at all unusual to be honest.

The best result will come from a center line pocket mount as far aft as you can go (but still 12-18" forward of the transom). That will also solve your issue with trailer bunks. I cannot tell from the photos, but I am guessing you have a sterndrive so you don't have shafts and rudders to worry about.

Next best would be to use a pair of tilted element transducers mounted close to the keel also far aft.

I have a twin inboard with a DFF-3D transducer in a pocket on the keel just forward of the stuffing boxes and a pair of tilted element B175s just forward of it. All three will maintain a clear picture up to about 26-28 kts unless the sea is rough. I get some noise above that speed.