Pontoon Boat & Deck Boat Forum

I've noticed yesterday that when I get my Bennington up to planing speed (around 3,000 rpm or so) the depth finder starts to flash the last depth I was at before advancing the throttle. As soon as I back the throttle down off planing speed, the unit starts to work again and display the proper depth.
Any ideas about what's happening? I'm thinking that it's kind of like cavitation, with the water around the sonar head becoming unstable.
Any idea how to fix it? I just emailed the dealer, but probably won't hear anything back for a day or two, but I'm curious if anyone else has experienced this.

I bet if you go to the back while running on plane and look down at the transducer you will see it is out of the flow of water. We had the same problem, lower the transducer so it is slightly below the bottom of the log and it should fix the problem. It did for us.

Yea, this is very common. Sometimes you have to adjust the angle of the transducer as well as the height. Just keep adjusting until you get the best read at all speeds. Good luck.

I had same problem and it was too high like said above, lowed it on the bracket and has been fine now for 5 years. Occasionally when I beach the boat I will kick the unit up on an angle and it will not read correctly, just have to take a pole and push it down level again. You don't want it to tight on the bracket because then it you hit something you know the plastic ears on the sonar will break off. It should be able to move under some pressure. Hope you get it corrected easily.

same problem here. as you get on plane, you also lift the transducer out of the water. as stated above, lower it a bit. may be the only down side to having a planing pontoon. fortunately its an easy fix.

I found that mounting the transducer on the transom works much better. The factory location causes much cavitation at speed from the V shaped protection running along the bottom of the toon. I'm also suspicious that the quality of the transducer may be in play also. See image of the two transducers ... left factory is Garmin 95 and one at transom is Huminbird/

I've got the same problem with my new HumminBird. Been on the phone over 5 hours with them (1/2 the time is waiting). The transducer is mounted in the exact same place as our old HumminBird transducer. 3,000 rpms it's fine, above that, gone. We've changed the angle of the transducer up/down, not much change.

It's not the engine's electrical system introducing an induced current cuz putting the boat in neutral & revving the engine above 4,000 rpms doesn't cause it to not read. And occasionaly it will read above 3,000 rpms, but not always. Our boat can't get up on a plane (Party Cruiser w/ 115hp outboard) & the tranducer is mounted in the exact same place (bottom of left toon) as the old one which worked fine even with one ear of the bracket broken.

We've tried everything the techs at HumminBird said to do, (filter settings & all) now we have to send the whole set-up in for them to check it. It's brand-new. WTF?

There is so much disturbed water coming from a pontoon is almost impossible to get a perfect reading at speed. You have to get the transducer deeper than a planing hull to the point it risks getting ripped off.
You may need to add to the mounting bracket to get it deep enough. Full length keels are bubble makers and near impossible to get clear reading. I have noticed on mine I loose any fish but still get a good bottom reading.
Face it having a toon ain't perfect platforms.

bassn386 wrote:I've noticed yesterday that when I get my Bennington up to planing speed (around 3,000 rpm or so) the depth finder starts to flash the last depth I was at before advancing the throttle. As soon as I back the throttle down off planing speed, the unit starts to work again and display the proper depth.
Any ideas about what's happening? I'm thinking that it's kind of like cavitation, with the water around the sonar head becoming unstable.
Any idea how to fix it? I just emailed the dealer, but probably won't hear anything back for a day or two, but I'm curious if anyone else has experienced this.

First guess would be the mounting height as everyone else has suggested. Second guess would be to see if your spark plugs are the R (resistor) type--they remove the high-powered radio noise that causes problems for a variety of electronics onboard.

http://www.ngksparkplugs.com/tech_suppo ... p?mode=nml

Thanks to everyone who has responded!
I'm out of town until the end of the week, but I will take a look at the mounting location and depth and play with it. I'll try the easiest first. The boat is on a lift and I don't have a trailer, so I'm somewhat limited in my initial options. I know my part of the lake pretty well, and I would not normally go full speed into an area I didn't know, so since going below 3,000 rpm doesn't have any effect, I should be okay until I can make some adjustments.
Thanks again; this is why I love this forum.

I played with the depth finder sender a lot on my boat over the years and I had the best luck with it on the motor bracket skid, aligned to the trailing edge like you do on a mono hull. It usually gets clean water there. Just be sure your motor doesn't trim down far enough to hit it.
In the last refit, I just took it off because I never really used it anyway.

Just checked our tranducer yesterday at speed (which on this boat is relative) and could amlost see it. Looks like it will have to be set deeper after all. (It's mounted in the same place as the old unit which worked but had a broken mount arm.)

I think I figured out what was wrong with my transducer. I noticed that it was pointed up rather than down, so I pushed on it gently but firmly and it rotated down about three clicks. At first I didn't think that was the answer, but I pushed it up to about 3,000 rpm where it had acted up and bingo, steady as a rock. No recurrence all afternoon. Simple fix this time.
Thanks to all for your help.