"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.