On Sun, 20 Aug 2006 07:51:21 +0200, "Steve Lusardi"
wrote:

It doesn't bounce around in the mineral oil. The tube fits the transducer
properly. The purpose of this is to allow transducer removal for maintenance
without hauling out, but it isn't for free. Even the best installations
attenuate the the transducer and performance suffers. On commercial ships,
they use a ball valved cavity that works much better.

Using that same technique, I installed a thru hull transducer system
earlier this year for use with my Furuno NavNet system. The sounder
module has a peak power of 600 watts and runs at 50 khz, 200 khz or
both. On the 50 khz setting we were getting reliable readings up to
about 1700 feet of water.

To say that I was surprised and impressed would be an understatement.

The transducer locks into a plastic housing which I bedded with 3M5200
and cured for 3 days before filling the housing with mineral oil. I'm
guessing at the thickness of fiberglass that the transducer is
shooting through but suspect that it is at least 3/4 inch, possibly
more.