Simrad AP28 Operator's Manual page 26

Spiral-turn
The spiral-turn feature may also be used for circling fish
or when searching a particular object on the seabed.
Spiral-turn makes the boat turn in a spiral with a
decreasing or increasing radius.
To enter Spiral-turn mode:
TURN
The "initial" radius can be set before the turn is started.
Press either the or key to select the direction in
which to make the spiral-turn and start.
During the turn the "change in radius" can be adjusted
and the number of feet or meter is how much the radius
is changed for each circle turned.
If the "change radius" is set to zero, the boat will turn in
a circle.
26 | Operation