Depth Switch

What it does

• Charts, echo sounders and pilot books may each use a different depth unit.
• The switch keeps a separate draft margin so it is never rounded away.
• Outputs are paired so the margin is visible next to every number.

How to use it

1. Set the echo sounder to the unit used by the chart you navigate from.
2. A fathom is six feet; converting in two steps invites a 10 per cent error.
3. Keep the draft margin separate from the under-keel clearance.
4. Write the unit on every depth in the log.

Safety notes

• A conversion cannot repair an unknown datum; see Chart Datum Shift first.
• Never reduce the margin to make a shallow entry work.