When I wanted to test whether an in-hull transducer would work in another boat, I read about a way to test a given location before doing something more permanent. Take a zip-lock bag, fill it with water and place it between the hull and the (powered) transducer. If you get readings that location will probably work.

While I'm sure plywood donuts work fine, I tend to use materials that are a little more permanent. I either pour epoxy in a small bucket and use a hole saw to make a donut, or cut one out of G-10 (the material used for printed circuit boards). YMMV

Mark

Boston, MA

2000 R22 *Luna Mia*

On Thu, Jul 28, 2022 at 1:17 AM <gstewart.gm at gmail.com> wrote:

> Larry:
> As requested I have attached a picture of my transducer install. This was
> a replacement install after my original knot log bit the dust. The first
> transducer was installed in a thru-hull located under the head. While this
> was a good location for the transducer the new transducer would not fit in
> the old thru-hull and rather than undertake the process of rebuilding the
> hole in the hull I decided to leave the old one in place and install the
> new one on the hull surface in the lazarette.
> My major concern about placing the transducer in the lazarette was
> protecting it from all the stuff that slides around when I heel - including
> an anchor.  I was unsure how well the transducer would work there so I
> wanted to be able to move it without destroying it or putting another hole
> in my boat. I placed the transducer just to the side and forward of the
> drain tube as this provided protection. The transducer fit nicely into 2"
> PVC tube so I cut a short length which I then inserted into an epoxy coated
> plywood donut that I cut with a hole saw and then epoxied the tube and base
> to the hull. This makes a very rugged enclosure. The transducer just sets
> in the tube. As I recall I used DAP sealant between the transducer and the
> hull. This sealant stays soft and allows the transducer to be removed if
> necessary. I fashioned a cap for the tube just to keep dirt out.
> I feel better about the enclosure than I do about the location. The
> transducer works but I get "out" errors for a split second every 10 seconds
> or so. I think that might be caused by bubbles created by the drain but
> can't be sure. The error does not interfere significantly with the use of
> the depth gauge so I am not inclined to move it to where it might be more
> exposed. My preference would have been to place it where the old one was
> under the floor in the head as the water is less disturbed there and it is
> in a safe yet accessible location.
>
>
>