Thread: false advertising?

makes good sense. I have done your brush study, and came to the same conclusions as I've inumetated here. ultimately I was unsuccessful in discovering any pattern that I could replicate consistently on the 998 in terms of DI

Originally Posted by rnvinc

I think some of the frustration in getting "picture perfect" DI images is that most structure (brush/etc) is not in the optimum position in the DI beam when the structure is seen on the display...

Most DI images are captured just by chance running over unknown structure or running over the waypoint marked on the chart...

A sonar beam (any shape sonar beam) is sometimes easily confused as having the same strength (reflective capability) in the entire size or width of the beam...giving the thought that "if I get the structure in the beam then it should show the same on the display no matter where the structure is placed in the beam...."

This is not how sonar works ...as defined by how sound actually travels thru water...

If we take the known factors in a DI sonar beam...(well any sonar beam in fact)...we find that the strongest sound reflection capability of the entire beam is in the exact center of the beam angle...and then the sound pulse weakens in an "ever-decreasing" strength until it completely dissipates into nothing...both in distance linearly from the xducer...and outward away from the centerline of the sound pulse..

What this mumbo jumbo means to the user is that "if" the structure (brush) is not in the exact center (the optimum strongest part of the sound pulse) of the beam angle ...then the "optimum" DI image is not going to be displayed on the screen...

The best "practice" for trying to learn settings for DI...is to physically find a good brushpile ...and I mean catch your bait in it ...not just see it on the display...and mark it with buoys...

Then run over the same brush over and over ...changing settings each pass until a pattern develops of how your specific unit responds to echos being received...in that particular enviroment where the "test" brush is located...

Once the settings have been determined for "what works best with my unit knowing the brush is definitely in the "optimum part of the DI beam"... Then future DI images of lesser quality could understandably be attributed to the possibility that ...maybe I just didn't get a good angle on "such and such" brushpile to get the best DI image...

Rickie