more

running.

Be careful where you mount the Fish Finder-they throw off lots of RDF which
may have an interesting effect on Loran or Radar  - if not carefully
shielded .

Can anyone tell me if the option described above (buying a fishfinder)
instead of trying to get repairs for the depth finder will work if  "gluing
the sending unit to a near horizontal section INSIDE (the) hull" will work
on a steel hull ???

Thanks in advance.

Jim Renforth
M/V General Brock
Valrico, FL

JRenforth@intermedia.com writes:

Had same discusioin with a neighbour who has a steel hull. Don't
know, but since i have a spare unit, will try in the next few weeks
and let you know. My hull is glass and I'm the one who originally
posted the fishfinder thing and it still works graeat after three
years.  Ciao- George of Scaramouche

Sue Culbreth wrote:

Hi Sue, just a suggested approach if you plan to do this yourself.
Start by masking off the floor along the cabinet so you don't mess up
your beautiful floors.  Then begin finish sanding at from 120 to 180
grit, unless you know for sure this has been done.  Otherwise, you could
get a blotchy appearance, due to some areas not being sanded.
Generally, a smoother surface will wind up lighter than one sanded to a
rougher grade.

Start out with a good grade of varnish, such as Z-Spar Captains.  Apply
3 coats, letting each coat dry b4 the next.  You can probably get the
1st 2 coats on the 1st day if you start in the AM.  After the 3rd coat
is good & dry, sand thoroughly with 180 grit and apply 3 more coats,
again letting the varnish dry betweeen coats.  Let this 6th coat fully
dry (usually a full day or 2), then sand with 220, 280 or 320 grit. This
will take from 4 to 5 days minimum.  You should now have pretty much a
filled-in surface, ready for applying the final "presentation" coat.  If
you want a satin finish, the final coat (or 2) sould be Minwax's
"Helmsman Spar Urethane" clear semi-gloss.  This is the only satin
finish that has a UV inhibitor, and is widely used on salon window sills
that get direct sun.  Gives a beautiful satin appearance.  Otherwise
just use the same varnish as build-up coats, and you should now have a
mirror-like finish.

Sorry for the long disertation.  You may get a number of techniques
offered, and any 1 of them may give good results.  Just don't start out
"experimenting" on your own, on your lovely new cabinet!  The real key
to a beautiful wooden finish is to 1st get the grain in the wood
completely filled; that's all you're doing for the 1st several coats of
whatever you choose to use . . .

All this material can be applied with foam 1&1/2 to 2" throwaway
brushes; don't even THINK about a bristle brush; way too much tedia
keeping it clean, and you still will get hairs coming out, driving you
absolutely nuts!!  I must say, I would recommend the above only to
someone who has varnishing experience.  Lacking that, I would start on a
side least visible. This will give an opportunity to get the feel for
varnishing (not too little, but not so much that you get runs).  Do just
that side thru the 1st 3 coats, sanding out any runs you might have with
#180.  Then repeat the process on the rest of the cabinet, and go on to
the remaining 3 coats.  The only critical coat is the last one (7th or
8th!)

P.S: If it's an option, you might even think about removing the cabinet
& taking it to a finishing shop, then re-installing.  Hope this helps &
best of luck . . .

Jim Hamlin,
Boatless for Now

Sue Culbreth wrote:

Sue, I'm sorry , I mis-read your note & thought it was a CABINET you
were finishing!!  However if you wind up choosing varnish, I would use
the same process I outlined in the previous note.  Just a tad more
inconvenient, having the whole salon vacated, waiting for the stuff to
dry . . .

At 04:57 PM 05/15/2000 -0400, you wrote:

Sorry for the late response. I just returned from a week long conference on
hydrography in Montreal.

The following  question was asked:

horizontal section INSIDE (the) hull" will work

Arild replies:

I spoke at lenght with  the design engineer  from AIRMAR a transducer
manufacturer who supply nearly 80% of all transducers  world wide.

First of all; NO,  gluing the transducer inside  a steel hull will not
work  because the  steel is NOT acoustically transparent.  Excessive
attenuation will occur and the depth sounder readings will not work  except
in very shallow water.

All transducers have  a "window" of accoustically  transparent  material;
even  those that are mounted inside a  steel casing which is welded to
stell hull plates.  These windows are usually  epoxy or polyurethane.  This
is why  it works on fibreglass hulls.

I would like to add a caution to  the  installation instructions when
applied to fibreglass.

Do not  use a "goop of  silicon caulking".  Quite often there are minute
air bubbles trapped in the  mass of caulking and  there are usually also
minute air pockets in the irregular surface  on the inner surface of most
molded hulls. The  smooth painted surfaces may still hide  minute air
pockets  in the glass matting.

I would go so  far as to sand smooth  the patch  area where you will stick
the transducer.

Airmar makes a specific mounting ring for just this application.  You cut
the tube at the specific angle  needed to match the deadrise of the hull.
The  tube is epoxied to the  inside  of the hull and the cavity is filld
with mineral oil. the  transducer is snapped into the locking  ring at the
top of the tube.  You now have a perfect acoustic coupling from the
transducer through the  oil and the  hull epoxy.

Lastly, I inquired about life expectancy of transducers in general.  I
wanted to know what factors contributed to a transducer "aging" and
eventually  not working.
The  transducer is composed of a ceramic material ( usually barium
titanate )  which  has a conductive  surface foil glued to  either side.
This piezo electric material  will flex mechanically when  an electric
pulse is applied.
Eventually the flexing causes the  foil to delaminate from the  transducer
material and  it quits working.  The delamination is usually progressive
so the process is characterized by  a progressively fainter and fainter
resonance as the  delaminated sction  enlarges.

The physical  size and shape of the  transducer element determines the
working frequency. Over time, this resonant frequency will change slightly.
If the  transducer  is subjected to shock  it may crack and this will
alter the frequency drastically  or perhaps render it  unresponsive to any
vibration mode.

Whats more  important, the  electronic circuitry  must remain stable at the
desired resonant frequency.  If that  frequency  is determined by a simple
RC network  then  the  frequency  will change drastically  as the resistor
and capacitor ages.
The simple fix will be to  retune the transmitter circuit;  a  tune-up
process that might have to be done every couple of years for maximum
efficiency.

I concur with the  recommendation to  replace a simple depth sounder with
a "fish finder "  simply because  these are so much more sophisticated in
the signal  processing and the resultant  graphic  display of  what  is
contained in the entire water column.
You not only  get a distance measurement  from the transducer face to the
bottom, but depending on  how the receiver works and what frequency is
used you can  see  sub surface details and  bottom cover like sediment,
plant growth and marine life  swimming in the water.

For what it's worth
I have no commercial interest in AIRMAR.  I was doing some basic research
for the  power squadron  manual  I am currently writing on depth sounders.

regards

Arild Jensen