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Considering a duel frequecy fishfinder 50/200khz. The 50 KHZ has a cone angle of 36 degs and the 200 has a 12 deg.

If my geometry if right. Tan (cone angle) X the depth of water = the area of the circle under your boat the fishfinder will see on the bottom.

Lets say I am fishing 300' water.

50 KHZ would pick up fish in a circle 218 Dia (big area)

200 KHZ 12 deg cone would be 64'

So if I only care about what is just under the boat or within a short cast when fishing deep water, why do people say the 50 khz is better in this case.

It appears that the best would be a narrow cone angle and a low frequency for truely deep water fishing.

I now have a 200 khz deg cone transducer and at the same depth it is showing a 42' dia circle which is all I need to see.

?

Capt. Marc