Thread: Sonar Quiz #41

Just looking at it, I would say it doesn't show because it's already been passed by & is out of range of the DI & 2d sonar pings.

If I could scroll back on the 2d & DI ... and it wasn't there, then, either ... I'd assume it was prop wash and not sufficient to stop the sonar penetration.

... cp

I think it is prop wash ..... which is surface disturbance. It looks like it goes deeper on the Si because the SI picks it up far off to the side ... and the only thing the transducer knows is how far something is from the tranducer, and the display shows it lower in the water column than it actually is.

I think there is merit to both of these answers. I see the prop wash as the big white arrow in the pic, and the boat trail as the blue divider line. The SI pics up the left side first from far away, and then crosses and the right side comes in close and recedes. I don't think the screen has scrolled beyond seeing, but I think maybe the "auto range" has put the echoes below the viewing area. (This way I get to be wrong two ways!)

I say prop wash also. The SI's image before your circle doesn't really look like a turn but I am sticking with prop wash.

The mass has already ran off the screen in 2D and DI.

Originally Posted by BobB

I think it is prop wash ..... which is surface disturbance. It looks like it goes deeper on the Si because the SI picks it up far off to the side ... and the only thing the transducer knows is how far something is from the tranducer, and the display shows it lower in the water column than it actually is.

This is a good explaination of why the prop wash "seems" to show "deeper" in the water column ...when in actuality the prop wash is being plotted as simply "farther away from the xducer" ...

Isn't it possible that because the DI fan beam and the 2d cone beam are very narrow at the xducer and spreads out as it decends downward ...that the prop wash (being close to the surface) is simply not in the reaches of the DI fan beam or the 2d cone beam ...??



Rickie

Originally Posted by rnvinc

Isn't it possible that because the DI fan beam and the 2d cone beam are very narrow at the xducer and spreads out as it decends downward ...that the prop wash (being close to the surface) is simply not in the reaches of the DI fan beam or the 2d cone beam ...??



Rickie

Exactly

So then I was basically right on both accounts. yay me

... cp