BUBBLED

Q: I own a 1998 Larson 223

IO. My depth gauge works well until about 2,300 rpm. Then it goes blank. If it slows back down to 2,300 rpm, it works OK. What can be wrong?

Gary Stribley Lake Okoboji, Iowa

A: Hi Gary. One of three things is the likely cause of your problem. First, if the transducer is mounted where it comes out of the water — or too near to the surface — as the boat rises when you accelerate, the signal will be lost as the transducer comes out of the water. Sonar does not work through air. Typically, the ’ducer is mounted somewhere about one-half the distance between the keel and chine on V-hulled boats.

Another cause for the symptoms you describe also relates to the transducer installation. If there is a hull fitting — like a strainer or intake or a lifting strake that terminates midship — directly forward of the ’ducer’s mounting location, it may be creating a bubble stream once a certain speed is reached. If the bubble stream runs over the transducer’s face or gets between the

’ducer and the bottom of the lake or ocean, the signal will be interrupted. Again, sonar does not work through air.

Third, you can try adjusting the power output (aka gain or sensitivity) of the depth sounder to maximum. Some low-power, inexpensive units need all of their output power to send and receive sufficient signal. Good luck!