80
Set Keel Offset
This unit measures water depth from the face of the transducer. Since
the transducer is installed below the water surface, the distance dis-
played by the digital depth, chart depth scale, chart cursor or fish sym-
bols is
not
the exact water depth. If the transducer is 1 foot below the
surface, and the screen shows the water depth as 30 feet, then the ac-
tual depth is 31 feet.
On sailboats or other large vessels with deep drafts, the distance be-
tween the transducer installation and the keel or lower engine unit can
be several feet. In those cases, an inexact depth reading could result in
grounding or striking underwater structure. The Keel Offset feature
eliminates the need for the navigator to mentally calculate how much
water is under his keel.
Keel Offset lets you calibrate the digital depth indicators: chart depth
scale, chart cursor depth and fish symbol depth displayed on the screen. To
calibrate the depth indicators, first measure the distance from the face of
the transducer to the lowest part of the boat. In this example, we will use
3.5 feet. We enter this as a
negative
3.5 feet, which makes the depth indica-
tors perform as if the transducer's lower in the water than it really is.
1. Press
MENU
|
MENU
|
↓
to
S
ET
K
EEL
O
FFSET
|
ENT
.
2. The Keel Offset dialog box appears. Press
↓
to so that the displayed
number shows a minus (–) sign instead of the plus (+) sign.
3. Press
↓
until the number shows – 3.5, then press
EXIT
. The depth
indicators now accurately show the depth of water beneath the keel.
NOTE:
If knowing the exact depth of water beneath the keel is less impor-
tant, you can calibrate the depth indicators so that they show the ac-
tual water depth from surface to bottom. To do this, first measure the
distance from the face of the transducer up to the surface (the water
line on the boat). In this example, we will use 1.5 feet. This will be en-
tered as a
positive
1.5 feet, which makes the depth indicators perform
as if the transducer's higher in the water than it really is.
