When looking at bridge equipment, a yacht owner may encounter several products described as an “anchor alarm”.
They can be very different systems.
The important distinction is not the display, the alarm sound or even how sophisticated the software is.
It is what the system actually measures.
An anchor alarm watches the yacht
A conventional GPS or GNSS-based anchor alarm monitors the position of the yacht.
A reference position or permitted movement area is established around the anchorage. If the yacht moves beyond that defined area, the system generates an alarm.
More advanced systems can take factors such as water depth and chain scope into account when calculating the permitted radius. That makes anchor alarms an extremely useful part of the bridge team’s situational awareness.
But the underlying measurement remains the position of the vessel.
The system therefore answers an important question:
Has the yacht moved somewhere we did not expect it to move?
From that movement, the crew can infer that the anchor may be dragging.
Anchor monitoring starts somewhere different
Direct anchor monitoring begins at the other end of the chain.
A sensor at the anchor or chain measures the position and movement of the anchor itself, independently of the yacht’s normal movement above it.
That changes the question being answered:
Is the anchor itself moving?
This matters because a yacht can swing, sheer or move as wind and current change without the anchor necessarily moving at all. Conversely, an anchor can begin to move without the yacht immediately travelling far enough to cross a vessel-position alarm boundary.
This is why GPS anchor alarms and direct anchor monitoring should not be treated as interchangeable technologies.
One does not make the other unnecessary
This is not an argument against GPS anchor alarms.
GPS, radar, electronic charts, visual bearings and established anchor-watch procedures all provide valuable information to a captain. Direct anchor monitoring simply adds another source of information that has historically been missing: what is actually happening at the anchor below the surface.
The European Commission described exactly this distinction when reporting on the original AnchorGuardian development: GPS identifies the position of the antenna aboard the vessel rather than the physical position of the anchor.
For a yacht owner, the technical terminology is less important than the principle.
When evaluating an “anchor alarm”, ask one simple question:
What is actually being measured?
The answer tells you far more about the system than the word alarm ever will.
A shout-out to Cintia Bianco for letting us use this free download picture.
