dragonfly 7 sonar images questions

[ray18]

Is my calculation of these 2 fish size correct?
I found these 2 fish huddled together at about 9 feet deep of water. I zoomed into water column between 7 feet and 9 feet. So, that's 2 feet of water. I know this sonar spots a 5 feet diameter circle cone in every 3 feet of water. Fish takes over about 60% of my screen. The fish size is about 2 feet = 60%*2*5/3 or 24 inches.

Do you agree?

[Chuck - Raymarine - Moderator]

Welcome to the Raymarine Forum ray18,

Please click here to view a FAQ related to this subject. The image size of an target appearing within the fishfinder plot will be dependent upon the physical of the object, its orientation and motion with respect to the motion of the boat, the speed that the boat is traveling, and in the case of fish, the size of their swim bladder. For example, should the vessel be stationary over an object suspended within the water column, then the target plotted by CHIRP (conical) sonar will appear as a more or less solid line at the depth of the object within the water column. A fast moving boat or objects moving at a high speed relative to the boat will produce smaller target images than would be produced by a slow moving boat or object moving a slow speed relative to the boat. All that one may typically infer is information about the relative size of object when two or more objects are plotted within the water column. Absolute sizes of objects would not typically be able to be determined.