[alberg30] Re: in hull transducer

Jack Vanderloo jvdloo at cyberus.ca
Wed Dec 9 07:06:27 PST 1998


From: Jack Vanderloo <jvdloo at cyberus.ca>

Ahoy Pete and Tom:
At the risk of jumping in uninvited on a discussion on "inhull"
transducers, but as a matter of interest for those with "thru’hull"
transducers, I’d like to relate my own experience with the location for
such a latter thru'hull transducer, namely, amidships, right on the bow,
in a custom glassed-in step.  Easy for fin-keeled boats; the difficulty
for Albergs is that in any other location, i.e. along the bilges, keel
shadow will give false readings when heeled (complaint of previous owner
and still a problem with the bilge-mounted paddle-wheel speed log).
Detail follows - greatly exaggerated and not truly reflective of how
unobtrusive and, more importantly, how protected it really is.
You may have to re-align the "x"s to reproduce the line of the bow.
       
                  x
                x
              x \ Bow
            x
          x
     xxxx
    x \
  x   \ Transducer - approx. 1 1/2' below water line
x       Max. horizontal and vertical exposure of leading edge of
transducer off natural line of bow = approx. 1/2"

The job was done professionally (by the builders of the Alberg 22, 29
and 34 - Nye Yachts in Canada), but should not be beyond the scope of a
competent DIYer.  I don't recall the diameter of the original hole
drilled - probably 2" - but this would of course be determined by one's
particular transducer.  The threaded transducer shaft will be a fairly
tightly fit inside the PVC pipe - see below.
>From near the forward edge, inside the small well just inside the
forepeak (about a foot and a half forward of the line of the main
bulkhead and just aft of where the water tank ends), they drilled
straight down to emerge on the bow line.  I’m certain a pilot hole was
drilled to establish actual depth of glass-work at that point - to
ensure the threaded shaft of the transducer would emerge inside and
out.  I seem to recall that they went through some 4" of glass(!).  A
heavy black PVC pipe - 2"? diameter - was then solidly glassed in, with
the exposed outside portion artistically shaped and faired into the line
of the underwater bow.  As noted above, the leading edge the pipe and
subsequent transducer faceplate is no more than ½" horizontally off the
natural line of the bow.  The aft edge of the pipe is recessed ½" up
from and ½" back off that same natural bow line.
The transducer is fitted inside the pipe, caulked on the outside and
secured firmly with the inside lock ring.  It has been on the boat since
1993, did 1925 nautical miles over three months on the Great Lakes this
summer, and has never given me the slightest amount of concern regarding
leakage or doubts about survivability in case of possible impact (the
transducer flange, where it buts against the minimally exposed,
glassed-in PVC pipe, presents a negligible surface).  Handsomely good
design and flawless functionality; can’t complain.
Cheers

Jack Vanderloo
ALDABI #641

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