Lowrance electronic Lowrance LMS-522c iGPS - Manual (Page 26)

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This will usually give you the best combination of smooth water flow
and protection from bangs and bumps.
Align transducer centerline with hull bottom.
However, there are times when you may need to adjust the transducer
slightly higher or lower. (The slots in the mounting brackets allow you
to loosen the screws and slide the transducer up or down.) If you fre-
quently lose bottom signal lock while running at high speed, the trans-
ducer may be coming out of the water as you cross waves or wakes.
Move the transducer a little lower to help prevent this.
If you cruise or fish around lots of structure and cover, your transducer
may be frequently kicking up from object strikes. If you wish, you may
move the transducer a little higher for more protection.
There are two extremes you should avoid. Never let the edge of the
mounting bracket extend below the bottom of the hull. Never let the
bottom – the face – of the transducer rise above the bottom of the hull.
Shoot-thru-hull vs. Transom Mounting
In a shoot-thru-hull installation, the transducer is bonded to the inside
of the hull with epoxy. The sonar "ping" signal actually passes through
the hull and into the water. This differs from a bolt-thru-hull installa-
tion (often called simply "thru-hull"). In that case, a hole is cut in the
hull and a specially designed transducer is mounted through the hull
with a threaded shaft and nut. This puts the transducer in direct con-
tact with the water.
Typically, shoot-thru-hull installations give excellent high speed opera-
tion and good to excellent depth capability. There is no possibility of
transducer damage from floating objects, as there is with a transom-
mounted transducer. A transducer mounted inside the hull can't be
knocked off when docking or loading on a trailer.
However, the shoot-thru-hull installation does have its drawbacks.
First, some loss of sensitivity does occur, even on the best hulls. This
varies from hull to hull, even from different installations on the same
hull. This is caused by differences in hull lay-up and construction.
Transom
Hull bottom
Transducer
centerline