You could run the 8 pin GT10HW 7-16 degree transducer on your 4 pin sounder with an adapter cable. In less than 30', the GT8HW you have is the one you want. In deeper (100'+), other variables come into play. But the one you have is probably fine. There are online calculators that will tell you what the bottom coverage is at various depths, and you can decide what is right for you.
Narrow beam transducers are primarily for saltwater. Only in Alberta is Cold Lake considered deep. lol.
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