Eagle Electronics SeaFinder 250 DF - Manual (Page 14)

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transducer up or down. If you frequently lose bottom signal lock while
running at high speed, the transducer 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 want, 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 "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 contact 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.
The shoot-thru-hull installation does have its drawbacks, though. 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.
Second, the transducer angle cannot be adjusted for the best fish
arches on your sonar display. Lack of angle adjustment can be par-
ticularly troublesome on hulls that sit with the bow high when at rest
or at slow trolling speeds.