Silicon attenuates too much (
http://scitation.aip.org/getabs/serv...cvips&gifs=yes )
, epoxy is much better. Mineral oil is very good, but it can be
messy/complicated. Ideally you want to match the speed of sound in the
materials to water to avoid high power reflections at the
transducer-epoxy-hull-water interfaces.

To bleed air bubbles from the epoxy, take an orbital sander put on a felt
pad and place it on the other side of the hull opposite the epoxy. The
vibration will bleed out the bubbles, do this before applying the transducer
and the epoxy must still be unhardened. Epoxy does sheer off in one nice big
chunk when removing. Also be sure to fill in the air bubbles in the
fiberglass mat of the hull if there are any.

Make sure you get a license before doing this!



wrote in message
...
On Fri, 29 Feb 2008 10:28:20 -0800, "Capt. JG"
wrote:

wrote in message
. ..
On Fri, 29 Feb 2008 09:39:45 -0800, "Capt. JG"
wrote:

"Phil Abuster" wrote in message
...
Transducers will work throught the hull from the inside if properly
mounted in a bed of epoxy.

Here's one example:

http://www.starmarinedepot.com/Rayma...ransducer.html

I've mounted a thru-hull inside the hull bedding in epoxy (make sure
no
air bubbles in epoxy) and it works great.


They don't need to be mounted in epoxy (those not going through the
hull)
to
work properly. They do need to not shoot through air. If you mount them
in
epoxy, you'll find it difficult to remove them if they fail.

Not difficult at all.

Well, it's not impossible, but it certainly easier if you don't have to do
it at all.


Actually, it's easier to remove one that is epoxied than it is to
remove all traces of silicone from one that is set in Silicone. I
removed one for a friend using a hammetr and a chisel. Took a lot less
time than when I had to deal with silicone residue n my own boat to
replace the install using epoxy. For that matter, if I was to do it
again, I wouldn't even worry about the existing puck, and would just
mount the new one in a different spot, like an inch away from the old
one. No removal is really needed.

In the method I
mentioned elsewhere, you don't have to be concerned with bubbles in the
epoxy because the transducer sits in mineral oil in a stable container
(one
that is epoxied to the hull in the appropriate spot).

The epoxy may not have bubbles in it to begin with, and if it does, it
is a very simple matter to remedy.

I'd really like to know how...

a sewing needle works very well.

how can you be sure one doesn't develop after
it hardens? I thought you said that it happened to you? Maybe I mis-read
that... a friend is contemplating the exact same type of installation.

No. The problem I had was after a few years, my silicone installation
apparently started to separate from the hull slightly (clear silicone
is NOT a good adhesive) and formed a gap that caused intermitant loss
of readings. I redid the install with epoxy and everything is fine.
The "possibility" of air bubbles is slight if you pour carefully, and
as I said, easy to remedy if there is a bubble or two.

I've done the old "tube full of oil" method, but its a lot more work,
and requires a spot with more space. It's also more vulnerable to
something knocking into it and causing it to leak. BTDT. That's why I
stopped doing them that way.



The main issue is
finding a spot via testing (as another suggested) before placing the
transducer holder.