Losing sonar depth reading at mid to hi throttle

[tony_cliffy]

I have my Lowrance transducer mounted to the bottom of my aluminum transom as per the instructions. The unit works great until I start to get some speed up (like in the 30's and 40's), then the depth indicator starts to flash and/or display unreal depths like 150 feet. I have tilted it a bit each way in the housing but it still happens. I have it about a quarter inch below the bottom of the hull but suspect my fairly flat bottomed boat (a 20' center console crestliner) is probably passing air/bubbles such that the transducer is getting too much noise between it and the water. I'm not sure how much deeper below the back of the transom I can adjust it given the available limits of travel left on the bracket. Plus putting it too far down seems like it is susceptible to striking water debris..<br /><br />So what the heck should I do? I don't like losing my depth reading at cruising speeds and just not sure of my available options. <br /><br />Thanks for any advice!<br /><br />TonyC

 

[DJ]

Re: Losing sonar depth reading at mid to hi throttle

tony,<br /><br />Have someone peer over the transom while you are at those troublesome speeds.<br /><br />I suspect you may have it mounted directly behind a strake. If anything, moving it to one side an inch or so may be the ticket.<br /><br />I always put a piece of starboard about 4" by 8* on the transom and attach the transducer to that.<br /><br />That way I only have two holes in the transom and can move the transducer as much as I want.

 

[tony_cliffy]

Re: Losing sonar depth reading at mid to hi throttle

For once I did something right, at least with the location. It is between two "strakes" or ribs. The ribs are about 8 or 10 inches apart and it is right in between them, maybe 20 inches to the right of the engine.<br /><br />I'll do the starboard next time. Good idea.

 

[DJ]

Re: Losing sonar depth reading at mid to hi throttle

Tony,<br /><br />That's good. You may even have it too deep. Have you tried raising it until it is just touching, when on plane.<br /><br />I think I know what boat you have. I think the bottoms of those are pretty smooth.

 

[randycc58]

Re: Losing sonar depth reading at mid to hi throttle

sometimes harmonics can fool depth finders. Mine did this for a while until I bit the bullet and mounted it inside the boat. Also cavitation under the boat can cause this. your instruction guide on installation should cover this. if not go to eagles web site and read the faq's. you should get some good ideas as to what to do

 

[Boatist]

Re: Losing sonar depth reading at mid to hi throttle

TonyCliffy<br />I think you did a pretty good job if it works to 30 mph. Aluminum boat create more bubbles than fiberglass boats. Today Crestliners are welded with no Rivets but older ones had some rivets in the main stringers. Rivets create air bubles at speed so transducer must be mounted deeper in the water to get below the air bubbles at speed. <br /><br />I also have a 1980 21 foot Crestliner I/O runabout and a 1982 Lowrance depth finder. Mine works to WOT but on my boat that is only 38 mph. However to get to work to WOT I have to turn down the sensitivy a little or the screen will black out with lots of false readings. When fishing I usually turn the sensitivy up until I get some false readings so to be sure and not miss any fish. Also if your depthfinder has a surface clutter control you might try turning that up a little and see if it helps.<br /><br />I feel the best starting postion for a depth finder is either side of the factory mounted Pitot tube. Most Pitot tubes are mounted far enough from engine as to not cause any caviation in turns and where factory thinks will have good water flow.<br /><br />On V hull the closer to the chims you mount your transducer the higher in the water it is. The chims at speed may even be out of the water or very shallow at speed. Also at speed your bow is turning a bow wave and then you run over the top of it. This bow wake water has lots of air in it and at sub planeing speed it is pushed out to the sides. At planeing speeds you run over this bow wake and that has lots of air in it. Since the wave is pushed to the side on a V hull you will have a lot more air as you get closer to the chims. About 12 inches from centerline is a good starting location for the transducer, or near the Pitot tube.<br /><br />Good Luck