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posted to rec.boats.electronics
Rob L.
 
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Default depth indication questions

I have some questions about depth finders and fish finders. I am looking at
basically just seeing how deep the water is while im at speed (old 16' volvo
penta unit so not extremely fast) pulling skiers and tubes. Will a fish
finder do this reliably or do i need a dedicated depth finder? I can get a
good deal on a piranha max 20 and was wondering if this unit could do the
job. Some have told me that this unit wouldnt work if I was going at any
rate of speed but I figured I would try here where the experts on this topic
seem to be located. I would also like the use of the fish finder for my
infrequent fishing trips but the depth indication is more what im looking
for in our shallow lakes up here.
Any comments or suggestions of a direction to go is very greatly
appreciated.


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posted to rec.boats.electronics
Larry
 
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Default depth indication questions

"Rob L." wrote in
newsQJjg.37697$A8.11468@clgrps12:

I have some questions about depth finders and fish finders. I am
looking at basically just seeing how deep the water is while im at
speed (old 16' volvo penta unit so not extremely fast) pulling skiers
and tubes. Will a fish finder do this reliably or do i need a
dedicated depth finder? I can get a good deal on a piranha max 20 and
was wondering if this unit could do the job. Some have told me that
this unit wouldnt work if I was going at any rate of speed but I
figured I would try here where the experts on this topic seem to be
located. I would also like the use of the fish finder for my
infrequent fishing trips but the depth indication is more what im
looking for in our shallow lakes up here.
Any comments or suggestions of a direction to go is very greatly
appreciated.




I had a Lowrance fish finder depth sounder in a 1997 Sea Rayder F16
jetboat going over 50 mph. At that speed, it could see the bottom in
60' of water from its INSIDE-THE-HULL transducer epoxied to the inside of
the bilge forward of the jet pump intake just offcenter of the keel. The
external transducer dragging in the water under jet power caused the boat
to steer towards the offcenter transducer's drag, making the boat loop
dangerously if it lost power suddenly.

The Lowrance got water in the display once about a year after I installed
it. Lowrance just gave me a new one....great service. Of course, I
bought it new.

Speed doesn't keep them from seeing the bottom....BUBBLES AND NOISE do.
If it's trying to see through the cavitation bubbles under the hull and
mechanical noise from the engine/drive, range drops quite badly. It will
not see through a cored hull like a Boston Whaler, either, because the
core absorbs the sound energy. Solid plastic or that chopper gun crap
they try to pass off as fiberglass these days seems to work well.

Hope this helped you.

  #3   Report Post  
posted to rec.boats.electronics
Rob L.
 
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Default depth indication questions

Thanks this info is of great help to me.
Now I now which route to go.


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posted to rec.boats.electronics
Ed
 
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Default depth indication questions

I have a $2000 unit and a $1200 unit on my sportfish with expensive
transducers, etc. They work OK at 20Kts but not over 200ft deep unless
I am going about 8Kts then it will read to 600ft..

I have a cheap humminbird piranha on my 40 kt jet dingy and it will read
to 50 ft plus at 40 kts. It is mounted INSIDE just like the other
poster suggested. I like it so much I bought another one for my little
whaler!!!





Larry wrote:
"Rob L." wrote in
newsQJjg.37697$A8.11468@clgrps12:


I have some questions about depth finders and fish finders. I am
looking at basically just seeing how deep the water is while im at
speed (old 16' volvo penta unit so not extremely fast) pulling skiers
and tubes. Will a fish finder do this reliably or do i need a
dedicated depth finder? I can get a good deal on a piranha max 20 and
was wondering if this unit could do the job. Some have told me that
this unit wouldnt work if I was going at any rate of speed but I
figured I would try here where the experts on this topic seem to be
located. I would also like the use of the fish finder for my
infrequent fishing trips but the depth indication is more what im
looking for in our shallow lakes up here.
Any comments or suggestions of a direction to go is very greatly
appreciated.





I had a Lowrance fish finder depth sounder in a 1997 Sea Rayder F16
jetboat going over 50 mph. At that speed, it could see the bottom in
60' of water from its INSIDE-THE-HULL transducer epoxied to the inside of
the bilge forward of the jet pump intake just offcenter of the keel. The
external transducer dragging in the water under jet power caused the boat
to steer towards the offcenter transducer's drag, making the boat loop
dangerously if it lost power suddenly.

The Lowrance got water in the display once about a year after I installed
it. Lowrance just gave me a new one....great service. Of course, I
bought it new.

Speed doesn't keep them from seeing the bottom....BUBBLES AND NOISE do.
If it's trying to see through the cavitation bubbles under the hull and
mechanical noise from the engine/drive, range drops quite badly. It will
not see through a cored hull like a Boston Whaler, either, because the
core absorbs the sound energy. Solid plastic or that chopper gun crap
they try to pass off as fiberglass these days seems to work well.

Hope this helped you.


  #5   Report Post  
posted to rec.boats.electronics
Larry
 
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Default depth indication questions

Ed wrote in news:jD4kg.73886$QU3.46747
@bignews8.bellsouth.net:

They work OK at 20Kts but not over 200ft deep unless
I am going about 8Kts then it will read to 600ft..



The trouble with deep is that sound travels so SLOW you get away before the
ping has time to go down that far and get back. What comes back is very
weak, at best. The other trouble is thermoclines at that depth. It's what
our subs hide behind so the "bad guys" lose them as the layers between
underwater layers of different temperature waters are quite impervious to
sonar sound, reflecting and absorbing the pings every time they go through
them. At long depths, you'll see the signal simply vanish, even though you
know the bottom's right where it was. The bottom at depth is also
undisturbed for millions of years. It's a soft composite of layers and
layers of whatever dies and falls to the bottom or what falls into the
water or what grows on the bottom. None of it is a nice, hard surface to
bounce pings off of.

If you ever meet a sub sonarman who's been at sea a while, ask him about
what the obstacles are. His sonar is HUGE with hundreds of transducers
listening intently for the sounds of the sea. He knows all the sea's queer
sound deadening phenomenon. I'm always in awe of their skills in hearing
and knowing what they hear in their profession. Those guys are some of the
most important on the boats.



  #6   Report Post  
posted to rec.boats.electronics
Ed
 
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Default depth indication questions

One I meet one I'll take him fishing so he can help me find the
yellow-eye snappers at 500'!!!

Thanks


Larry wrote:
Ed wrote in news:jD4kg.73886$QU3.46747
@bignews8.bellsouth.net:


They work OK at 20Kts but not over 200ft deep unless
I am going about 8Kts then it will read to 600ft..




The trouble with deep is that sound travels so SLOW you get away before the
ping has time to go down that far and get back. What comes back is very
weak, at best. The other trouble is thermoclines at that depth. It's what
our subs hide behind so the "bad guys" lose them as the layers between
underwater layers of different temperature waters are quite impervious to
sonar sound, reflecting and absorbing the pings every time they go through
them. At long depths, you'll see the signal simply vanish, even though you
know the bottom's right where it was. The bottom at depth is also
undisturbed for millions of years. It's a soft composite of layers and
layers of whatever dies and falls to the bottom or what falls into the
water or what grows on the bottom. None of it is a nice, hard surface to
bounce pings off of.

If you ever meet a sub sonarman who's been at sea a while, ask him about
what the obstacles are. His sonar is HUGE with hundreds of transducers
listening intently for the sounds of the sea. He knows all the sea's queer
sound deadening phenomenon. I'm always in awe of their skills in hearing
and knowing what they hear in their profession. Those guys are some of the
most important on the boats.


  #7   Report Post  
posted to rec.boats.electronics
Larry
 
Posts: n/a
Default depth indication questions

Ed wrote in news:I3lkg.58308$qd2.32459
@bignews6.bellsouth.net:

One I meet one I'll take him fishing so he can help me find the
yellow-eye snappers at 500'!!!


One of the best times of my life was a "Friends and Family Cruise" I took
with a friend, who was a first class radioman, but has now been promoted to
Ensign and really deserves it, aboard USS Pennsylvania (SSBN-735), one of
our fine Trident submarines, a few years ago.

Sitting in the sonarman's seat, listening intently to the sea in his
headphones, you get to listen in on a whole other world you have no idea
exists under the surface. Having Pennsylvania's expert sonar chief give
you the guided tour is like being admitted to a secret world few ever get
to experience.

It was an amazing day this old destroyerman will never forget....

I'll sail with the finest Navy crews on the planet, again, any time I'm
asked. What an honor it was to be there.

  #8   Report Post  
posted to rec.boats.electronics
Wayne.B
 
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Default depth indication questions

On Wed, 14 Jun 2006 23:38:53 -0400, Ed wrote:

I have a $2000 unit and a $1200 unit on my sportfish with expensive
transducers, etc. They work OK at 20Kts but not over 200ft deep unless
I am going about 8Kts then it will read to 600ft..


I have a 600 watt Furuno Navnet sounder connected to an inexpensive
thru-hull transducer. We get reliable depth readings up to about 1600
feet at trawler speeds of 8 to 10 knots.

  #9   Report Post  
posted to rec.boats.electronics
William Andersen
 
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Default depth indication questions

Just remember that at speed, if there's a sand bar - you'll be on it before
the depth/fish finder can indicate that you've run out of water!

"Rob L." wrote in message
newsQJjg.37697$A8.11468@clgrps12...
I have some questions about depth finders and fish finders. I am looking

at
basically just seeing how deep the water is while im at speed (old 16'

volvo
penta unit so not extremely fast) pulling skiers and tubes. Will a fish
finder do this reliably or do i need a dedicated depth finder? I can get

a
good deal on a piranha max 20 and was wondering if this unit could do the
job. Some have told me that this unit wouldnt work if I was going at any
rate of speed but I figured I would try here where the experts on this

topic
seem to be located. I would also like the use of the fish finder for my
infrequent fishing trips but the depth indication is more what im looking
for in our shallow lakes up here.
Any comments or suggestions of a direction to go is very greatly
appreciated.




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