On Mon, 09 Jun 2008 09:28:39 +0200, Salomon Fringe
wrote:

Hi all, I want to upgrade my echo sounder but I find that all of the
units I am looking at give up at around half a meter - unlike my 20
years old unit that I wanted to replace (I need zero depth performance
for inland waterways). Does anybody know of a unit/brand/type that would
work for me? I'm not interested in fish, just displaying depth.

With the newer digital units, you can degrade the sensitivity down
that the return ping is discriminated against the noise. Even the
cheaper units are 800 watt so you are dealing with power problem
decreasing the sensitivity would help a lot.

You will be hard pressed to find a single frequency transducers for
200 KHz which is what you are looking for - 50 Hz units are for deeper
water - more than 30'.

So, simply put, you need to find a digital unit where you can select
200 KHz and be able to decrease the sensitivity enough to get zero
depth performance. I have a Raymarine DS-500 that is selectable to
200 KHz or you can use the dual function and decrease the sensitivity
to find dead bottom.

The only other thing I would recommend is a single frequency depth
flasher which is different from a full sonar. Those work in a
different fashion and most of the new ones are 200 KHz which will give
you depth discrimination without having the mess around with menus.
Some are programmable, some aren't.

I wouldn't recommend anything specific because this is a special
circumstance and you have to fit your needs to what is available on
the market. Hope that helps a little.

Now, with respect to zero depth performance - pardon my ignorance but
I'm curious why you would be running around in zero depth waters. Do
you have a deep draft sailboat or cruiser of some sort?