I've got an old (to say the least !) Lowrance GPS/ Sonar unit LMS-350A on a 24' Explorer. When I get up on plane, I'll be traveling along getting reasonable depth readings ( 4-10') when all of a sudden I'll be reading 180' - 3xx' ! ... BTW, I've got a 225HP O/B and the transducer is transom mounted on the starboard side of the engine, between it and the trim tab. Is this normal operation of the sonar unit or am I experiencing a malfunction of some sort ?
Sonar Transducer
- Thread starter wrg49
- Start date
You might check and see if the transducer has hit something and kicked up from the correct position. Sounds like that be the case.
wrg49 said:
It should be tight. Lowrance ducers have a bolt that runs through the bracket and the mounting area of the ducer. Depending on how old it is... some have rubber friction washers, (spacers) and some have detents, or teeth built in that hold it in position. In either case, it should be tight enough that a decent amount of force is required to "kick" it up.
Make sure the bottom surface of the ducer is paralell with the running surface of the hull, and slightly, (about 1/8"+) below the bottom of the hull, when you tighten it up. See below.
The height shouldn't have changed, just the angle... but you never know. And if it did, you'll need to loosen the bracket mounting screws on the transom. Remove one at a time completely and re-seal with 3M 4200, 5200, Life seal, etc. You might want to replace the screws with new ones while your at it.
Imo, the newer, smaller Lowrance ducers don't have a lot of "meat" on the mounting area. They crack and break pretty easy. On the plus side... they hold a signal at high speed very well.
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Mine looks exactly like the one above and works great at all speeds and sea conditions (Lowrance X70A).
Caution is that the paddlewheel next to it disappeared, speed was accurate at Trolling speed and wildly optimistic at cruise speed,
temperature used to be accurate and now reads high.
Seems you must replace the entire speed sender, (just the paddle wheel is not available) hate to go through re-running a new cable.
Mine looks exactly like the one above and works great at all speeds and sea conditions (Lowrance X70A).
Caution is that the paddlewheel next to it disappeared, speed was accurate at Trolling speed and wildly optimistic at cruise speed,
temperature used to be accurate and now reads high.
Seems you must replace the entire speed sender, (just the paddle wheel is not available) hate to go through re-running a new cable.
wrg49 said:
Assuming this didn't happen before, there are several possibilities. First as mentioned is transducer position. Its easy to take a look and see if it is level to the water. It must also as mentioned be set so that the bottom surface is slightly below the bottom of the hull. That's harder to check in the water. Check the bottom of the transducer for barnacles. Just one can cause turbulence.Turbulence from other sources will cause these kinds of readings also. Did anything change on the rigging? (motor prop, tabs etc).
It is unlikely that the transducer is bad as long as it seems to operate correctly at lower speeds.
Thanks to everyone for the great input !
This is my second season with this boat, so I don't know if the previous owner was experiencing the same problems. I do know that the transducer does swing up quite easily, so that may be the problem occuring at higher speeds. I'll also check the mounting location to be sure its at the right level. Thanks again !
This is my second season with this boat, so I don't know if the previous owner was experiencing the same problems. I do know that the transducer does swing up quite easily, so that may be the problem occuring at higher speeds. I'll also check the mounting location to be sure its at the right level. Thanks again !
It shouldn't swing easily. If you can reach it, try to flip it up. It it goes easily, it needs to be tightened or the bracket is bad.wrg49 said:
These things are pivi=oted so that in theory if it hits something it tolts up. When it does, it doesn't flop back down so unless yours is really loose, flipping up isn't the problem.
I've also noticed that there is some of the ablative bottom paint on the transducer.. Can that be causing a problem too ? .. can it be safely removed without harming the transducer ?