On Mon, 09 Jun 2008 19:24:42 +0000, Larry wrote:

What I always thought we needed was a sort of underwater "curb feeler"
like we used to put on the pimpmobiles. A couple of stiff wires that
would protrude down into the water 3 ft from the BOW that would make an
awful griding noise

Such devices exist.

They are frequently called propellers.

Wayne.B wrote in
:

On Mon, 09 Jun 2008 19:24:42 +0000, Larry wrote:

What I always thought we needed was a sort of underwater "curb feeler"
like we used to put on the pimpmobiles. A couple of stiff wires that
would protrude down into the water 3 ft from the BOW that would make an
awful griding noise

Such devices exist.

They are frequently called propellers.


When they grow up on steroids, we call them "screws", which make contacting
the bottom with them MUCH more exciting!

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.

I have a garmin with the transducer mounted inside my fiberglass hull, and
it can read as shallow as the two foot range with no problem, and I've seen
it go as shallow as 1.2-1.8.
On several occasions I've also seen it measure double the actual depth in
shallow water, but that is a rarity. I assume when that happens that it is
measuring the second bounce off of the hull.
Having the transducer mounted inside the hull may reduce the sensitivity,
enhancing the shallow water performance. I mounted it with silicone seal,
rather than hard epoxy, and I don't have a problem with water up to
100-ft(deepest I've been) in sal****er. I used the silicone seal, since I
wasn't sure how well it would work in that location, and I wanted to make it
easy to move. It worked so well, I never re-installed it with the epoxy.
To install the transducer inside the hull, take the end from a spray paint
cap and cut the remaining collar to the hull angle and glue it down. After
it sets, put about 3/8" of silicone into it and push the transducer into it.
I can't remember if I positioned the transducer bottom flush with the hull
or vertical.

On Jun 9, 8:29*pm, Short Wave Sportfishing
wrote:
On Mon, 09 Jun 2008 19:50:06 -0400, RLM wrote:
On Mon, 09 Jun 2008 23:31:21 +0000, Short Wave Sportfishing wrote:

On Mon, 09 Jun 2008 11:04:13 -0400, wrote:

In a sailboat, the transducer would be mounted in the hull, above the
level of the top of the keel, so you would have 4-10 feet (depending
on how deep a keel you have) of water even with the keel scraping
bottom. Sounders usually have a "keel offset" setting to compensate
and tell you how much depth remains after the keel height is
subtracted.

I understand that - I'm not clear on the whole zero depth concept.

If the water's muddy and you can see the bottom that's the zero depth
concept or just use the acronym ZDC.

The sounder is the noise the hull makes scrapping in the mud.

That's kind of my point. *Zero depth implies no water. *If there is no
water, why do you need a depth finder?- Hide quoted text -

- Show quoted text -

And if there's an engine involved, there may well be an overheating
problem.

Thanks all for all the replies, couldn't reply until now because I am
cruising. Hadn't expected such a great response either ;-)
Of course, about zero depth, I am not referring to water just a few
centimers deep (...) but to water that is close to 0 below the
transducer. The thing is that my more than 20y old unit that I had
wanted to replace *is* able to measure as little as 15cm below the keel.
My trawler-style boat has about a 25cm difference between fore and aft
so if I were to mount it at the best (highest) position I would still
have a gray zone of 25cm with the transducers I am looking at (50cm min
depth), and I don't like that. There are quite a few harbours where I
have less than 50cm below the keel, and if so I want to know how much
exactly e.g. to predict if I am going to hit the bottom in a falling tide.

A Furuno rep actually told me I should look at a simple smart sensor
depth-only device (similar to advice given in this thread) so I guess
the big improvement I am looking for (depth graph) is not in the cards
for me. Can't believe that sounder technology has made no major
improvements in this sense for more than 20 years.

Something else is that I have two sea chests with transducers, one with
the old digital depth meter I am using and the other from a Lowrance
X16. That unit has been enjoying its retirement somewhere on the sea
bottom for years now but the transducer is still there and apparently
works at a funny frequency, 196khz. Is there any way to detune any brand
of 200khz sounder to work with this unit? If not I have no other option
than to have the transducer replaced.

Some people said I am asking for the impossible when I asked for a
near-zero-water-below-the-keel sounder, but when you do the math it sure
doesn't seem impossible, at 200khz one cycle takes 5 microseconds, the
speed of sound in water is approx. 1500m/s so in principle you should be
able to measure down to 0,75 cm. About 1/3 of an inch. Perhaps you can't
make the pulse that short or something, dunno.

S

On Jun 11, 1:49*pm, Salomon Fringe wrote:
Thanks all for all the replies, couldn't reply until now because I am
cruising. Hadn't expected such a great response either ;-)
Of course, about zero depth, I am not referring to water just a few
centimers deep (...) but to water that is close to 0 below the
transducer. The thing is that my *more than 20y old unit that I had
wanted to replace *is* able to measure *as little as 15cm below the keel..
My trawler-style boat has about a 25cm difference between fore and aft
so if I were to mount it at the best (highest) position I would still
have a gray zone of 25cm with the transducers I am looking at (50cm min
depth), and I don't like that. There are quite a few harbours where I
have less than 50cm below the keel, and if so I want to know how much
exactly e.g. to predict if I am going to hit the bottom in a falling tide.

A Furuno rep actually told me I should look at a simple smart sensor
depth-only device (similar to advice given in this thread) so I guess
the big improvement I am looking for (depth graph) is not in the cards
for me. Can't believe that sounder technology has made no major
improvements in this sense for more than 20 years.

Something else is that I have two sea chests with transducers, one with
the old digital depth meter I am using and the other from a Lowrance
X16. That unit has been enjoying its retirement somewhere on the sea
bottom for years now but the transducer is still there and apparently
works at a funny frequency, 196khz. Is there any way to detune any brand
of 200khz sounder to work with this unit? If not I have no other option
than to have the transducer replaced.

Some people said I am asking for the impossible when I asked for a
near-zero-water-below-the-keel sounder, but when you do the math it sure
doesn't seem impossible, at 200khz one cycle takes 5 microseconds, the
speed of sound in water is approx. 1500m/s so in principle you should be
able to measure down to 0,75 cm. About 1/3 of an inch. Perhaps you can't
make the pulse that short or something, dunno.

S

It's not sending a single 360 degree cycle. It's sending a short
pulse of 200 khz and then waiting for the return. The duration
defines how shallow it can read, not the frequency.

"Salomon Fringe" wrote in message
...
Thanks all for all the replies, couldn't reply until now because I am
cruising. Hadn't expected such a great response either ;-)
Of course, about zero depth, I am not referring to water just a few
centimers deep (...) but to water that is close to 0 below the transducer.
The thing is that my more than 20y old unit that I had wanted to replace
*is* able to measure as little as 15cm below the keel.
My trawler-style boat has about a 25cm difference between fore and aft so
if I were to mount it at the best (highest) position I would still have a
gray zone of 25cm with the transducers I am looking at (50cm min depth),
and I don't like that. There are quite a few harbours where I have less
than 50cm below the keel, and if so I want to know how much exactly e.g.
to predict if I am going to hit the bottom in a falling tide.

A Furuno rep actually told me I should look at a simple smart sensor
depth-only device (similar to advice given in this thread) so I guess the
big improvement I am looking for (depth graph) is not in the cards for me.
Can't believe that sounder technology has made no major improvements in
this sense for more than 20 years.

Something else is that I have two sea chests with transducers, one with
the old digital depth meter I am using and the other from a Lowrance X16.
That unit has been enjoying its retirement somewhere on the sea bottom for
years now but the transducer is still there and apparently works at a
funny frequency, 196khz. Is there any way to detune any brand of 200khz
sounder to work with this unit? If not I have no other option than to have
the transducer replaced.

Some people said I am asking for the impossible when I asked for a
near-zero-water-below-the-keel sounder, but when you do the math it sure
doesn't seem impossible, at 200khz one cycle takes 5 microseconds, the
speed of sound in water is approx. 1500m/s so in principle you should be
able to measure down to 0,75 cm. About 1/3 of an inch. Perhaps you can't
make the pulse that short or something, dunno.

S

To get very close, you would have to have two transducers. Actually one
transmitter and one receiver. The ringing in the transmitter is one of the
major timing restrictions. You have to wait until the electronic eddy
currents dampen out before you can look for a received signal. And the new
units have more power and higher frequencies so you get better definition,
but the ringing is worse, so you have the 2-3' of not readable water below
the transducer.

On Wed, 11 Jun 2008 19:49:31 +0200, Salomon Fringe
wrote:

Thanks all for all the replies, couldn't reply until now because I am
cruising. Hadn't expected such a great response either ;-)
Of course, about zero depth, I am not referring to water just a few
centimers deep (...) but to water that is close to 0 below the
transducer. The thing is that my more than 20y old unit that I had
wanted to replace *is* able to measure as little as 15cm below the keel.
My trawler-style boat has about a 25cm difference between fore and aft
so if I were to mount it at the best (highest) position I would still
have a gray zone of 25cm with the transducers I am looking at (50cm min
depth), and I don't like that. There are quite a few harbours where I
have less than 50cm below the keel, and if so I want to know how much
exactly e.g. to predict if I am going to hit the bottom in a falling tide.

A Furuno rep actually told me I should look at a simple smart sensor
depth-only device (similar to advice given in this thread) so I guess
the big improvement I am looking for (depth graph) is not in the cards
for me. Can't believe that sounder technology has made no major
improvements in this sense for more than 20 years.

Something else is that I have two sea chests with transducers, one with
the old digital depth meter I am using and the other from a Lowrance
X16. That unit has been enjoying its retirement somewhere on the sea
bottom for years now but the transducer is still there and apparently
works at a funny frequency, 196khz. Is there any way to detune any brand
of 200khz sounder to work with this unit? If not I have no other option
than to have the transducer replaced.

Some people said I am asking for the impossible when I asked for a
near-zero-water-below-the-keel sounder, but when you do the math it sure
doesn't seem impossible, at 200khz one cycle takes 5 microseconds, the
speed of sound in water is approx. 1500m/s so in principle you should be
able to measure down to 0,75 cm. About 1/3 of an inch. Perhaps you can't
make the pulse that short or something, dunno.

Holy smokes - an X-16? Dude - you need to move up to the 21st
Century. :)

What kind of unit did the 196 KHz transducer connect to?

On Wed, 11 Jun 2008 11:27:33 -0700 (PDT), wrote:

On Jun 11, 1:49*pm, Salomon Fringe wrote:
Thanks all for all the replies, couldn't reply until now because I am
cruising. Hadn't expected such a great response either ;-)
Of course, about zero depth, I am not referring to water just a few
centimers deep (...) but to water that is close to 0 below the
transducer. The thing is that my *more than 20y old unit that I had
wanted to replace *is* able to measure *as little as 15cm below the keel.
My trawler-style boat has about a 25cm difference between fore and aft
so if I were to mount it at the best (highest) position I would still
have a gray zone of 25cm with the transducers I am looking at (50cm min
depth), and I don't like that. There are quite a few harbours where I
have less than 50cm below the keel, and if so I want to know how much
exactly e.g. to predict if I am going to hit the bottom in a falling tide.

A Furuno rep actually told me I should look at a simple smart sensor
depth-only device (similar to advice given in this thread) so I guess
the big improvement I am looking for (depth graph) is not in the cards
for me. Can't believe that sounder technology has made no major
improvements in this sense for more than 20 years.

Something else is that I have two sea chests with transducers, one with
the old digital depth meter I am using and the other from a Lowrance
X16. That unit has been enjoying its retirement somewhere on the sea
bottom for years now but the transducer is still there and apparently
works at a funny frequency, 196khz. Is there any way to detune any brand
of 200khz sounder to work with this unit? If not I have no other option
than to have the transducer replaced.

Some people said I am asking for the impossible when I asked for a
near-zero-water-below-the-keel sounder, but when you do the math it sure
doesn't seem impossible, at 200khz one cycle takes 5 microseconds, the
speed of sound in water is approx. 1500m/s so in principle you should be
able to measure down to 0,75 cm. About 1/3 of an inch. Perhaps you can't
make the pulse that short or something, dunno.

It's not sending a single 360 degree cycle. It's sending a short
pulse of 200 khz and then waiting for the return. The duration
defines how shallow it can read, not the frequency.

Um - by definition it's sending 360 degree cycles - about 2 million of
them.

wrote:
On Jun 11, 1:49 pm, Salomon Fringe wrote:

Some people said I am asking for the impossible when I asked for a
near-zero-water-below-the-keel sounder, but when you do the math it sure
doesn't seem impossible, at 200khz one cycle takes 5 microseconds, the
speed of sound in water is approx. 1500m/s so in principle you should be
able to measure down to 0,75 cm. About 1/3 of an inch. Perhaps you can't
make the pulse that short or something, dunno.

S


It's not sending a single 360 degree cycle. It's sending a short
pulse of 200 khz and then waiting for the return. The duration
defines how shallow it can read, not the frequency.

I realise that, but I suppose the sounder calculates the depth based on
receipt of the wavefront of that pulse. To determine it is receiving
its own signal it needs at least a 360. I'm just guessing here because
it seems that in reality they need much more than one cycle.