Select Setup > Marine.

Marine Chart Mode

Sets the type of chart the device uses when displaying marine data. Nautical displays various map features in different colors so the marine POIs are more readable and so the map reflects the drawing scheme of paper charts. Fishing (requires marine maps) displays a detailed view of bottom contours and depth soundings and simplifies map presentation for optimal use while fishing.

Appearance

Sets the appearance of marine navigation aids on the map.

Marine Alarm Setup

Sets alarms for when you exceed a specified drift distance while anchored, when you are off course by a specified distance, and when you enter water of a specific depth.