75
If the transducer is 1 foot below the surface and the screen shows the
water depth as 30 feet, then the actual 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, 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 indicators
perform as if the transducer is lower in the water than it really is.
1. Press
MENU
|
MENU
|
↓
to
S
ONAR
S
ETUP
|
ENT
.
2. Select
S
ET
K
EEL
O
FFSET
and press
ENT
.
3. The Keel Offset dialog box appears. Press
↓
so the displayed number
shows a minus (–) sign instead of the plus (+) sign.
3. To change the next digit, press
→
then use
↑
↓
to enter 3. Move to
the next digit and enter 5, then press
EXIT
. The depth indicators now
accurately show the depth of water beneath the keel as -3.5.
NOTE:
If knowing the exact depth of water beneath the keel is less impor-
tant, you can calibrate the depth indicators so they show actual water
depth from surface to bottom. To do this, measure the distance from
the face of the transducer to the surface (the water line on the boat).
In this example, we will use 1.5 feet. This will be entered as a
positive
1.5 feet, which makes the depth indicators perform as if the trans-
ducer is higher in the water than it really is.
Summary of Contents for Cada 250 S/Map
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