If you wore shoes that were 10ft square, would you feel a small hole?
The first thing the "ping" hits returns an echo.
If you have a 6ft "hit" on the bottom & you go over a 7ft hole you will get
an echo from the bottom of the hole.
If you go over a 4ft hole you won't see it.
That's my understanding anyway.
BruceM


"LD" wrote in message
ink.net...
I currently have an inexpensive fish/bottom finder with a 20deg cone angle
and am having very much trouble locating "obstructions" on the bottom
where
I fish (in the gulf out of Pensacola). Many of these were points were
converted from Loran to GPS and only go to 2 decimal places, or within
52.8ft. My GPS might be within 10-20ft and the 20deg cone, at 50ft, if my
trig is right, is just over 18ft. Most of my fishing would be in the 40
to
100' depths.
In short, it takes a lot of passes to locate a car body or even a larger
object such as a sunken tug or barge.
I think the Hummingbird Matrix 37 with a 90/20 dual cone or the Eagle
Trifinder with up to a 150deg cone would help locate these wrecks.

Is my logic good? Am I missing something?