Depth sounders to show negative numbers
 

Does anyone know if there is a depth sounder which shows a negative depth.
OK sounds like a loony question.
I have a lift keel boat and want to set the offset when there is no water
under the keel with the keel down. Same as all sensible people with fixed
keel boats. Easy to do with my Raymarine ST60 Tridata echo sounder. Now if I
raise the keel to go into shallower waters, there isn't 7 ft (2.2m) of water
in a lot of places on the East Coast of England, I still want to know how
much water there is underneath me. Hence I need to find an echo sounder that
shows 0.0m with no water under the keel when down, an say -0.7m when the
depth is 0.7m less than with the keel fully down.
Hence my question. I should have thought with the number of lift keel boats
there would be a reasonable demand, and lets face it, it isn't rocket
science to make a minus sign show up on a LCD display

On Mon, 4 Apr 2005 23:50:24 +0100, "Phil Stanton"
wrote:

Does anyone know if there is a depth sounder which shows a negative depth.
OK sounds like a loony question.
I have a lift keel boat and want to set the offset when there is no water
under the keel with the keel down. Same as all sensible people with fixed
keel boats. Easy to do with my Raymarine ST60 Tridata echo sounder. Now if I
raise the keel to go into shallower waters, there isn't 7 ft (2.2m) of water
in a lot of places on the East Coast of England, I still want to know how
much water there is underneath me. Hence I need to find an echo sounder that
shows 0.0m with no water under the keel when down, an say -0.7m when the
depth is 0.7m less than with the keel fully down.
Hence my question. I should have thought with the number of lift keel boats
there would be a reasonable demand, and lets face it, it isn't rocket
science to make a minus sign show up on a LCD display

A lot of "sensible" people I know would set the offset so the unit
reads actual depth, which incidentally corresponds to the numbers on
the charts, providing an additional navigational check. These same
sensible people seem to have no trouble remembering how much water
they draw. Weird, I know. :-)

Glen
__________________________________________________ __________
Glen "Wiley" Wilson usenet1 SPAMNIX at world wide wiley dot com
To reply, lose the capitals and do the obvious.

Take a look at cpRepeater, my NMEA data integrator, repeater, and
logger at http://www.worldwidewiley.com/

I've tried the "depth below keel" approach. I found that the depth sounder
should show the depth of the water itself. Do the various conversions in
your head. Knowing the true depth helps with setting the anchor, etc.

Doug

"Phil Stanton" wrote in message
...
Does anyone know if there is a depth sounder which shows a negative depth.
OK sounds like a loony question.
I have a lift keel boat and want to set the offset when there is no water
under the keel with the keel down. Same as all sensible people with fixed
keel boats. Easy to do with my Raymarine ST60 Tridata echo sounder. Now if
I raise the keel to go into shallower waters, there isn't 7 ft (2.2m) of
water in a lot of places on the East Coast of England, I still want to
know how much water there is underneath me. Hence I need to find an echo
sounder that shows 0.0m with no water under the keel when down, an
say -0.7m when the depth is 0.7m less than with the keel fully down.
Hence my question. I should have thought with the number of lift keel
boats there would be a reasonable demand, and lets face it, it isn't
rocket science to make a minus sign show up on a LCD display

Well sensible people may have the privilege of sailing in deeper waters than
here on the East Coast. At low water, there is frequently about 1.5m and
most of us, reluctantly have to scrape along with 0.1m under the keel if we
are lucky. Added to that there are a number of us who are always sailing on
each others boats, and it is nice to know if the echo sounder says 0.2m,
regardless of which boat you are on, that is what you have got under you.
I take your point about anchoring, but I guess we drop the anchor once for
every 20 or 30 times we are scraping the bottom.

Phil

"Glen "Wiley" Wilson" wrote in
message ...
On Mon, 4 Apr 2005 23:50:24 +0100, "Phil Stanton"
wrote:

Does anyone know if there is a depth sounder which shows a negative depth.
OK sounds like a loony question.
I have a lift keel boat and want to set the offset when there is no water
under the keel with the keel down. Same as all sensible people with fixed
keel boats. Easy to do with my Raymarine ST60 Tridata echo sounder. Now if
I
raise the keel to go into shallower waters, there isn't 7 ft (2.2m) of
water
in a lot of places on the East Coast of England, I still want to know how
much water there is underneath me. Hence I need to find an echo sounder
that
shows 0.0m with no water under the keel when down, an say -0.7m when the
depth is 0.7m less than with the keel fully down.
Hence my question. I should have thought with the number of lift keel
boats
there would be a reasonable demand, and lets face it, it isn't rocket
science to make a minus sign show up on a LCD display

A lot of "sensible" people I know would set the offset so the unit
reads actual depth, which incidentally corresponds to the numbers on
the charts, providing an additional navigational check. These same
sensible people seem to have no trouble remembering how much water
they draw. Weird, I know. :-)

Glen
__________________________________________________ __________
Glen "Wiley" Wilson usenet1 SPAMNIX at world wide wiley dot com
To reply, lose the capitals and do the obvious.

Take a look at cpRepeater, my NMEA data integrator, repeater, and
logger at http://www.worldwidewiley.com/

Thanks Doug

See my reply to Glen

Phil


"Doug Dotson" dougdotson@NOSPAMcablespeedNOSPAMcom wrote in message
...
I've tried the "depth below keel" approach. I found that the depth sounder
should show the depth of the water itself. Do the various conversions in
your head. Knowing the true depth helps with setting the anchor, etc.

Doug

"Phil Stanton" wrote in message
...
Does anyone know if there is a depth sounder which shows a negative
depth. OK sounds like a loony question.
I have a lift keel boat and want to set the offset when there is no water
under the keel with the keel down. Same as all sensible people with fixed
keel boats. Easy to do with my Raymarine ST60 Tridata echo sounder. Now
if I raise the keel to go into shallower waters, there isn't 7 ft (2.2m)
of water in a lot of places on the East Coast of England, I still want to
know how much water there is underneath me. Hence I need to find an echo
sounder that shows 0.0m with no water under the keel when down, an
say -0.7m when the depth is 0.7m less than with the keel fully down.
Hence my question. I should have thought with the number of lift keel
boats there would be a reasonable demand, and lets face it, it isn't
rocket science to make a minus sign show up on a LCD display

On Tue, 5 Apr 2005 09:45:11 +0100, "Phil Stanton"
wrote:

Well sensible people may have the privilege of sailing in deeper waters than
here on the East Coast. At low water, there is frequently about 1.5m and
most of us, reluctantly have to scrape along with 0.1m under the keel if we
are lucky.

Interesting theory, but I'm on Florida's Gulf coast. Water is pretty
skinny here. Anything over 4 feet is considered deep draft.


Added to that there are a number of us who are always sailing on
each others boats, and it is nice to know if the echo sounder says 0.2m,
regardless of which boat you are on, that is what you have got under you.

And having your sounder read negative numbers helps this how? Since
this is a problem, maybe you should just stencil your draft on your
bulkheads in fluorescent chartreuse numbers to help each other out.
:-)

I take your point about anchoring, but I guess we drop the anchor once for
every 20 or 30 times we are scraping the bottom.

Hope you find what you're looking for.

Phil

__________________________________________________ __________
Glen "Wiley" Wilson usenet1 SPAMNIX at world wide wiley dot com
To reply, lose the capitals and do the obvious.

Take a look at cpRepeater, my NMEA data integrator, repeater, and
logger at http://www.worldwidewiley.com/

"Phil Stanton" wrote in message
...
Does anyone know if there is a depth sounder which shows a negative depth.
OK sounds like a loony question.
I have a lift keel boat and want to set the offset when there is no water
under the keel with the keel down. Same as all sensible people with fixed
keel boats. Easy to do with my Raymarine ST60 Tridata echo sounder. Now if
I
raise the keel to go into shallower waters, there isn't 7 ft (2.2m) of
water
in a lot of places on the East Coast of England, I still want to know how
much water there is underneath me. Hence I need to find an echo sounder
that
shows 0.0m with no water under the keel when down, an say -0.7m when the
depth is 0.7m less than with the keel fully down.
Hence my question. I should have thought with the number of lift keel
boats
there would be a reasonable demand, and lets face it, it isn't rocket
science to make a minus sign show up on a LCD display



Hi Phil,
If that's what you like, it can be done with a Brookhouse NMEA multiplexer.
They do much more than NMEA combining/multiplexing alone. Maybe we should
rename them "NMEA controllers" or something.
One of the functions is NMEA sentence editing "on the fly", i.e. real-time
editing of NMEA parameters, as the sentences pass through the multiplexer.
Editing directives can be uploaded to the multiplexer in setup mode.
http://brookhouseonline.com/pdf%20fi...%20Editing.pdf
We have recently added a new editing directive, for making adjustments to
fields in NMEA sentences, which is ideal for depth offsets, water-speed
correction etc.
The *A directive allows you to add or subtract a signed value from any given
NMEA parameter field of any specified sentence and if the result is
negative, it places a minus-sign in front of it. Of course it re-calculates
the sentence-checksum.
If you connect a repeater instrument to the multiplexer RS422 output and
program it for depth, you'll get exactly what you want, provided you use a
repeater that displays the NMEA field exactly as found in the sentence. You
won't need a new depthsounder. Your ST60 instrument will be suitable as
there is an option for Seatalk to NMEA conversion. Adjust the offset of the
ST60 to display actual water depth and set the "correction" in the
multiplexer to -7.0 and you will get negative depths on the repeater for any
depths under 7 feet.
Wout

Hi Wout

Thanks for the information. I will definitely investigate this further, as
in addition to the depth problem, I am having problems getting my Laptop to
talk to the Autopilot. May be a wiring fault, but apparently the ST60 multi
instrument has NMEA In and Out.
Back to the depth problem. Have you any idea which display instruments will
display a -(minus) sign.
Thanks again for starting me off in the right direction

Phil



"Wout B" wrote in message
...

"Phil Stanton" wrote in message
...
Does anyone know if there is a depth sounder which shows a negative
depth.
OK sounds like a loony question.
I have a lift keel boat and want to set the offset when there is no water
under the keel with the keel down. Same as all sensible people with fixed
keel boats. Easy to do with my Raymarine ST60 Tridata echo sounder. Now
if
I
raise the keel to go into shallower waters, there isn't 7 ft (2.2m) of
water
in a lot of places on the East Coast of England, I still want to know how
much water there is underneath me. Hence I need to find an echo sounder
that
shows 0.0m with no water under the keel when down, an say -0.7m when the
depth is 0.7m less than with the keel fully down.
Hence my question. I should have thought with the number of lift keel
boats
there would be a reasonable demand, and lets face it, it isn't rocket
science to make a minus sign show up on a LCD display



Hi Phil,
If that's what you like, it can be done with a Brookhouse NMEA
multiplexer.
They do much more than NMEA combining/multiplexing alone. Maybe we should
rename them "NMEA controllers" or something.
One of the functions is NMEA sentence editing "on the fly", i.e. real-time
editing of NMEA parameters, as the sentences pass through the multiplexer.
Editing directives can be uploaded to the multiplexer in setup mode.
http://brookhouseonline.com/pdf%20fi...%20Editing.pdf
We have recently added a new editing directive, for making adjustments to
fields in NMEA sentences, which is ideal for depth offsets, water-speed
correction etc.
The *A directive allows you to add or subtract a signed value from any
given
NMEA parameter field of any specified sentence and if the result is
negative, it places a minus-sign in front of it. Of course it
re-calculates
the sentence-checksum.
If you connect a repeater instrument to the multiplexer RS422 output and
program it for depth, you'll get exactly what you want, provided you use a
repeater that displays the NMEA field exactly as found in the sentence.
You
won't need a new depthsounder. Your ST60 instrument will be suitable as
there is an option for Seatalk to NMEA conversion. Adjust the offset of
the
ST60 to display actual water depth and set the "correction" in the
multiplexer to -7.0 and you will get negative depths on the repeater for
any
depths under 7 feet.
Wout

Phil,
Repeaters that can be programmed to display any NMEA data (ASCII
characters), will display whatever is in the depth data field in the DBT
sentence, including the minus sign (put there by the multiplexer, as
explained) The Cruzpro repeater instrument would be a good candidate.
If you already have the ST60 Multi, you can try if it will display a
negative depth by creating a DBT sentence on your laptop with Notepad. Put
e.g. -5.5 in the depth field. Save the sentence in a file. Connect the COM
port of your laptop to NMEA IN of the ST60 instrument (pin 3 to NMEA IN +,
Gnd to NMEA -) and send the .txt file containing the sentence to the
instrument with Hyperterminal (@4800bps, no parity, no flow control). Repeat
this is couple of times and check what the instrument displays. First
configure the instrument for NMEA input, of course.
Wout






"Phil Stanton" wrote in message
...
Hi Wout

Thanks for the information. I will definitely investigate this further, as
in addition to the depth problem, I am having problems getting my Laptop
to
talk to the Autopilot. May be a wiring fault, but apparently the ST60
multi
instrument has NMEA In and Out.
Back to the depth problem. Have you any idea which display instruments
will
display a -(minus) sign.
Thanks again for starting me off in the right direction

Phil



"Wout B" wrote in message
...

"Phil Stanton" wrote in message
...
Does anyone know if there is a depth sounder which shows a negative
depth.
OK sounds like a loony question.
I have a lift keel boat and want to set the offset when there is no
water
under the keel with the keel down. Same as all sensible people with
fixed
keel boats. Easy to do with my Raymarine ST60 Tridata echo sounder. Now
if
I
raise the keel to go into shallower waters, there isn't 7 ft (2.2m) of
water
in a lot of places on the East Coast of England, I still want to know
how
much water there is underneath me. Hence I need to find an echo sounder
that
shows 0.0m with no water under the keel when down, an say -0.7m when
the
depth is 0.7m less than with the keel fully down.
Hence my question. I should have thought with the number of lift keel
boats
there would be a reasonable demand, and lets face it, it isn't rocket
science to make a minus sign show up on a LCD display



Hi Phil,
If that's what you like, it can be done with a Brookhouse NMEA
multiplexer.
They do much more than NMEA combining/multiplexing alone. Maybe we
should
rename them "NMEA controllers" or something.
One of the functions is NMEA sentence editing "on the fly", i.e.
real-time
editing of NMEA parameters, as the sentences pass through the
multiplexer.
Editing directives can be uploaded to the multiplexer in setup mode.
http://brookhouseonline.com/pdf%20fi...%20Editing.pdf
We have recently added a new editing directive, for making adjustments
to
fields in NMEA sentences, which is ideal for depth offsets, water-speed
correction etc.
The *A directive allows you to add or subtract a signed value from any
given
NMEA parameter field of any specified sentence and if the result is
negative, it places a minus-sign in front of it. Of course it
re-calculates
the sentence-checksum.
If you connect a repeater instrument to the multiplexer RS422 output and
program it for depth, you'll get exactly what you want, provided you use
a
repeater that displays the NMEA field exactly as found in the sentence.
You
won't need a new depthsounder. Your ST60 instrument will be suitable as
there is an option for Seatalk to NMEA conversion. Adjust the offset of
the
ST60 to display actual water depth and set the "correction" in the
multiplexer to -7.0 and you will get negative depths on the repeater for
any
depths under 7 feet.
Wout

Phil Stanton wrote:
Hi Wout

Thanks for the information. I will definitely investigate this further, as
in addition to the depth problem, I am having problems getting my Laptop to
talk to the Autopilot. May be a wiring fault, but apparently the ST60 multi
instrument has NMEA In and Out.

A good way to trouble shoot NMEA data problems is to use the
Hyperterminal communications utility included with Windows. That will
show you the NMEA data flow as scrolling ascii text strings. And the
strings can even be saved to a text file for later study.

To use it, select the COM port your NMEA data is on in the "Connect
using:" box. Then change the settings to 4800 baud, 8 data bits, parity
to none, and stop bits to 1. If your NMEA data is at a different baud
rate you may have to change that, the display will be repeated garbles
when that happens. Sometimes you can check the setup on your NMEA
talkers to see what baud rate is being used, they all need to be the same.

Seeing the NMEA data strings tells you your laptop setup is working and
can help you isolate the problem.

There is a known problem with Windows misidentifying a GPS or NMEA input
as a serial mouse. If you go to the device manager find a serial mouse
there, disable it and leave it disabled and that will not happen again.

Jack

--
Jack Erbes in Ellsworth, Maine, USA - jackerbes at adelphia dot net
(also receiving email at jacker at midmaine.com)