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Raymarine forum - a98 Chirp & Down Vision view of bottom

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I went to FAQ and I have copied and pasted examples below
in example 1,
Chirp, at 100' the area on the bottom I am looking at is a 44.34' area?
Which would be similar to the traditional to the view of a 50Khz?


Example #1 CHIRP (conical) sonar cone base diameter at depth:
.... cone base diameter at 100' depth = 0.4434 * 100' = 44.34'


For the examples below, at 100' the area at the bottom I am looking at is 1.' ft wide and 115.4' long?


Example #2: DownVision side to side axis dimension at depth:


DownVision side to side axis dimension at depth:100' = 115.4'

Example #3: DownVision fore to aft axis dimension at depth:

.... fore to aft axis dimension at 100' depth = 0.01222 * 100' = 1.222''
No Free Rides,

Q1. Chirp, at 100' the area on the bottom I am looking at is a 44.34' area?
Which would be similar to the traditional to the view of a 50Khz?
A1. The diameter of cone at any specified depth is dependent upon cone angle produced by the transducer elements. 50KHz transducers are not all identical with respect to cone angle. Should the cone angle of the 50kHz transducer which you have referred to also have a cone angle of 25 degrees, then the diameter at depth would be the same.

Q2. For the examples below, at 100' the area at the bottom I am looking at is 1.' ft wide and 115.4' long?
A2. Incorrect. With respect to DownVision, each ping (vertical line) plotted by the sonar reflected a beam with is is approximately 60 degrees in the side to side axis and 1.4 degrees in the fore/aft axis. At 100', this would correspond to a footprint which is 1.2' in the fore-aft axis and 115' in the port-starboard axis. As the sonar scrolls, fine fore-aft axis images combine to produce a detailed image of structure.
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