Sonar gone when on plane..

[wipe_out]

Hi,

Just wondering if it's normal for the sonar to vanish when the boat is on a plane.. It's a Lowrance 7 HDS gen 2 with the transom mounted transducer.. Works fine at low speed but when on a plane it appears to see nothing, not even a depth reading.. Is that normal?

 

[BruceK]

Transom mounted transducers need to be in clean water. If you have a step in the hull, chines etc that cause turbulent aerated water under the transducer when on the plane they will not perform. Try moving it.

 

[oldgit]

Hi,

Just wondering if it's normal for the sonar to vanish when the boat is on a plane.. It's a Lowrance 7 HDS gen 2 with the transom mounted transducer.. Works fine at low speed but when on a plane it appears to see nothing, not even a depth reading.. Is that normal?

No. !

 

[Kempy]

Hi,

Just wondering if it's normal for the sonar to vanish when the boat is on a plane.. It's a Lowrance 7 HDS gen 2 with the transom mounted transducer.. Works fine at low speed but when on a plane it appears to see nothing, not even a depth reading.. Is that normal?

I have a similar issue with my boat. Over a certain speed the deep reading stops. I consider this normal. Its been the same for the last two boats I have owned. By transom mounted transducers. Over 15kn and the readings stop

 

[colingr]

As BruceK said, the transducer needs to be in a clean flow of water. Mine works up to 40 knots quite happily. Moving it away from the prop and from any chines will help. Sometimes a small movement can make all the difference. Also make sure it is horizontal and hasn't been knocked up at an angle.

 

[sprocker]

I agree, aerated water is no good for transducer readings.

I have the same Lowrance kit on my MF645, but mounted my transducer internally to shoot thru' hull. I get good depth readings through the full range of speeds.

 

[wipe_out]

I have the same Lowrance kit on my MF645, but mounted my transducer internally to shoot thru' hull. I get good depth readings through the full range of speeds.

Interesting.. Just clarify that for me.. You mounted the transom mount transducer inside the hull? Or you bought a different transducer?

 

[wipe_out]

I'll have to have a closer look at the position and location to see if there in anything obvious causing the issue..

 

[Danfarry]

Mines the same, mounted internally with no hole through the hull. Boat is an Antares 8.8

 

[sprocker]

Interesting.. Just clarify that for me.. You mounted the transom mount transducer inside the hull? Or you bought a different transducer?

It was the standard transducer, just mounted inside the hull, inside a sealed container filled with water or thin oil. The only thing you don't get with this method of mounting is true water temp.

 

[wipe_out]

It was the standard transducer, just mounted inside the hull, inside a sealed container filled with water or thin oil. The only thing you don't get with this method of mounting is true water temp.

Good to know.. If I don't come right with it hanging out the back I will look at changing the location..

 

[colingr]

If you're going to mount it internally you need to make sure that there are no air gaps between the transducer and the outside on the hull. if you bond it directly to the hull you also need to be very careful not to have any bubble in the epoxy or whatever you use.

Best to bond a bit of open pipe to the hull then fill with a light oil before mounting the transducer inside.

 

[sprocker]

Best to bond a bit of open pipe to the hull then fill with a light oil before mounting the transducer inside.

Exactly the way I've always done it JB, used that method in my fishing kayaks also.

 

[wipe_out]

Best to bond a bit of open pipe to the hull then fill with a light oil before mounting the transducer inside.

When you say "light oil" what are you meaning exactly?

 

[wipe_out]

Exactly the way I've always done it JB, used that method in my fishing kayaks also.

Don't suppose you have a photo or two so I can see how you did it in case I have to go that route?

 

[Mike k]

remember the dead rise angle too. I fitted the Airmar P79 - its has its own base 'tube thing' but needs to set at the correct angle ( mine was 20 degrees} so it looks directly vertically down. P.s I used Propylene glycol as recommended not oil

 

[maverickofpoole]

To help find the best location to shoot through the hull you can us Blue Tack or Plasticine to temporary fix your transducer to the boat. This allows you to move the transducer from place to place to find the best location. You can then fix permanently using either the Resin, Bath or Silicone methods described by others all of which will work

 

[MapisM]

Mine works up to 40 knots quite happily.

Do you mean a transom transducer? If so, may I ask you which brand/model it is? Regardless, chapeau to whoever installed it.
I'm not exaggerating if I guesstimate to have cruised in more that a couple of dozen of different boats equipped with them, and never saw one reliably working with the boat steadily planing.

 

[LadyJ]

I too have the Lowrance HdS 7 Gen 2, I had similar type issues (also showed some obviously incorrect readings) and got the dealer to change the transducer (same location) and have had no problem at all at any speed (I cruise at 24 knots and periodically blast at 34 knots). Happy to note position and let you know to check it's the same place as yours as we have the same boat.

 

[GrahamHR]

In recent years, since 2001 I've had 3 boats with transom mounted fishfinder transducers. All fitted by me.

#1 Humminbird
#2 Garmin
#3 Lowrance

All fitted according to OEM recommendations worked well at all speeds. The last, the current one this year worked well after launch but later in the season tended to lose signal at higher speeds, I think though that was due to turbulence due to quite extensive fouling resulting from very few hours use. The transom mounted speedo paddle wheel was also totally encrusted with sea weed and tube worms, as were the props.