Roger Long wrote:
The in hull transducer on my boat works great. It's just slapped on
the inside of a fairly thick hull.

I can't imagine putting a hole in a hull if you don't need to.

I experimented with shooting through the hull, and directly by
dangling the transducer over the side prior to permanent installation.
Shooting through the hull reduced the maximum range of the depthsounder
by about 25%. The solid FG hull thickness was about 5/8". A yard guy
said experiment with exact placement if you do shoot through the hull,
as a void or dry spot in the laminate directly below the transducer can
reduce the maximum range by a lot.

One good thing you can do with a shoot through the hull setup is orient
the transducer so it points straight down on a curved hull surface, by
using an adjustable mount (available from manufacturer) which immerses
the transducer in mineral oil. The gizmo is a tube with an angled
flange on the bottom which is glued (with 5200) to the hull, and a
sealing threaded top for the transducer.

My through hull mounted transducer is flush on a curved part of the
hull, about 20 degrees out of plumb, so I get greater range on the
tack which plumbs the transducer. When heeled 30 degrees on the "bad"
tack, the maximum range drops by over 50%. This is with a high
frequency 200khz trandsucer which has a fairly narrow emission cone;
the effect should be less with a 50khz transducer, as its emission cone
is wider.

Oh, and it's an inexpensive depthsounder with a rated maximum range of
200 feet.