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Determining the diameter of the bottom scanned by a fishfinder xducer
02-27-17, 04:34 PM (This post was last modified: 04-21-17 09:49 AM by Chuck - Raymarine - Moderator.)
Post: #1
Determining the diameter of the bottom scanned by a fishfinder xducer
Determining the diameter of the bottom sounded by a fishfinder transducer

The primary variables determining the diameter of the area being sounded by a fishfinder transducer are 1) the cone angle / beam angle of the transducer and the depth of the water or depth of the object within the water column beneath the transducer. The cone angle of the CPT-S Transducers and the CHIRP (conical) element CHIRP (conical) / DownVision transducers designed for use with an ax8 MFD, eSx8 MFD, a CP100 CHIRP (conical) / DownVision Sonar Module, and Dragonfly products is 25 degrees. The cone angle for other Raymarine transducers may be found within the corresponding specifications web page for the respective transducer.

The diameter of the cone at any depth may be computed using some basic trigonometry:

[Image: marija1.1.gif]

Cone Radius = tan (B) x Cone Height

Cone Radius = tan (Transducer Cone Angle / 2) x Depth
Cone Diameter = 2 x Cone Radius = 2 x tan (Transducer Cone Angle / 2) x Depth


Example 1: The depth of the water beneath the transducer is 100'. The depth of fish marked by the fishfinder is 30'. Determine the cone diameter being sounded by the CHIRP (conical) element (25 degree cone angle) of eS98 MFD's CHIRP/DownVision Transducer for these depths:

Cone Diameter = (2 x tan (Cone Angle / 2)) x Depth
Cone Diameter = (2 x tan (25 deg / 2)) x Depth
Cone Diameter = (2 x tan (12.5 deg)) x Depth
Cone Diameter = (2 x 0.2217) x Depth
Cone Diameter = 0.44338 x Depth

Cone Diameter at Bottom = 0.44338 x 100' = 44.34'
Cone Diameter at the Depth of a Fish marked at 30' depth = 0.44338 x 30' = 13.30'

Example 2: The depth of the water beneath the transducer is 100'. The depth of fish marked by the fishfinder is 30'. Determine the cone diameter being sounded by the 200 kHz element of my eS97 MFD's B744V transducer (12 degree cone angle for 200 kHz) for these depths:

Cone Diameter = (2 x tan (Cone Angle / 2)) x Depth
Cone Diameter = (2 x tan (12 deg / 2)) x Depth
Cone Diameter = (2 x tan (6 deg)) x Depth
Cone Diameter = (2 x 0.1051) x Depth
Cone Diameter = 0.2102 x Depth

Cone Diameter at Bottom = 0.2102 x 100' = 21.02'
Cone Diameter at the Depth of a Fish marked at 30' depth = 0.2102 x 30' = 6.31'


It should additionally be noted that the A-Scope feature of the supported by Raymarine fishfinding products will also report the cone diameter at the bottom of the water column beneath the transducer.


RAYFAQ#


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