Finder not working at higher speeds

[brushpile]

I just installed a Lowrance 135 on my boat. I decided to go ahead and drill into the transom for the transducer mount. No leaks, but I have a problem. I get a great picture on my screen while cruising, but when I'm at full speed (about 40 mph) the sonar will not pick up the bottom. It will either flash or give a totally inaccurate depth reading.

The directions stated that you should mount it in between the ribs closest to the engine on an aluminm boat, but you should maintain at least 1 foot from the lower unit. I mounted my transducer about 13 inches from the lower unit.

Do I need to remount the transducer over a little farther away from the engine? If I do this, how should I fill the 2 holes at the bottom of my transom?

Thanks,

[FishMan]

mine works good at hi speeds but it doesn't help me. no matter how much I practice I just can't get that cast right when going 40 MPH. I even slowed down to 30 in case the fish were having a hard time keeping up but still, no bites.

Good Morning

[loanwizard]

I have the same problem with my Jet Drive. I would check to see if the transducer is low enough. The midline of the transducer should be level with the bottom of the boat. I have a 135 too.

[craigr]

I have seen this complaint on several boards, in magazines & mentioned in instruction manuals. They all say the first thing to check is water flow at the problem speed. - As mentioned above, the transducer is constant & good contact with the water.

craigr

[Nobody Special]

If your boat is a riveted hull, then the rivets could be causing air bubbles. Also the weld seam at the transom. I've found that it's very difficult getting readings at higher speeds with an aluminum hull. Try lowering the transducer a little and make sure it's tilted down at the back just a little and if that don't help, you might be better off just living with it than ending up with holes all over the transom.

[jim]

Michael makes an excellent point.Most boats ride bow up at speed so the transducer is no longer looking straight down.Adjust it with the correct angle and also remember water conditions are going to have an impact.If the water is rough or you cross a wake the angle is going to change and your unit might temporarily lose bottom lock.This is normal and it should regain the proper depth when the boat settles out.:smile2:

[brushpile]

Thanks for all the help. My boat is a flat bottom and I believe the angle is set pretty well. The midline of the transducer is in line with the bottom of the boat. I will try moving it down a little and if that doesn't help, I'll live with it.

By the way, I'm interested in getting an accurate depth reading at high speeds, not finding structure or fish.

Thanks again for all the replies

[vlparrish]

Brian, I understand your situation. If you are running WOT and the depth finder is not working properly. It could be possible to run a ground before you know what hit you. I'm with everyone else, try lowering your transducer a little. I hope it works for you. Vern

[Whistler]

Had the same problem with my new one. Lowered it one inch and it works great now. Mine's on a pontoon boat. I'd say lower it down a bit further.

[brushpile]

Thanks again, I should know if lowering the transducer worked the next time I head to the lake.

[Cheez]

Brian I have a G3 jon boat. I have tried 3 different sonar units. It came with a Garmin 160 (blew out @ 15 mph). I changed it to a Lowrance 135 because the dealer said I needed more power. The 135 has 4000 wats peak to peak power. It blew out @ 20 mph. I sent it back to Cabela's and got a Humminbird 777c2. It is the best by far of the three but it blows out @ 28 mph. I moved them up,down,left and right. I changed the angle on all of them so many times it made me sick. Then my dealer said that they never have been able to get a sonar to work on any G3 jon boat at speed. I now have accepted this fact, I don't like it even a little but have accepted it. By the way I also have 10 holes in my transom.
I don't know what kind of boat you have but hope you have more success than I did.

Cheez