Settings / Anchor Monitor

Anchor Alarm

The Anchor Monitor can (1) estimate the location of your anchor on the seabed and (2) trigger an alarm when your it detects your vessel moving too far from that location.

This monitor improves on the simple alarm most mariners are accustomed to. When setting your anchor, the monitor estimates the actual location on the seabed where the anchor is set. It does this by accounting for the GPS antenna's position relative to the bow, your current heading, and the scope you have let out. After the anchor is set, the estimated location is displayed, along with the predicted circle of swing and alarm circle.

The extra accuracy can be helpful when you wake up in the middle of the night and check if your anchor is dragging. You can clearly see the location and orientation of your vessel relative to the original estimated anchor location and swing circle. Improved accuracy may allow use of a smaller alarm radius, so you can get an earlier warning when dragging begins. It can also be helpful when maneuvering your vessel's bow above the anchor to raise it.

All calculations are based on the location where the anchor (normally) attaches to your vessel, the bow. The Monitor uses your vessel's size, position of GPS antenna, (as specified in the Vessel True-scale settings) and heading to identify the location of your bow. It works best when using your vessel's GPS with a fixed antenna location on your vessel. When using an mobile device, of course results will vary as the device is moved within the vessel.

If all this sounds complicated, that is fine. You can use a value of zero for Scope. Then the Alarm Distance can be used in similar manner to a basic anchor alarm. You may also want to use a zero scope in more complex anchoring situations, such as when using multiple anchors.




While Anchoring

We recommend setting the anchor position during the normal process of anchoring, at the point when the anchor has been physically set into the seabed and your vessel is backed up on it. The rode should be somewhat straight and your vessel's bow pointed toward where the anchor is set. At that point you should also know approximately how much scope is out.


When you return to the Navigate tab, a black anchor symbol will be at the estimated location of your anchor. There will also be a black dotted circle indicating the scope radius and a dashed circle for the alarm. You need to be at most 1:20,000 scale for circles to be shown.

Changing Alarm

After setting the anchor you can change it by single tapping on the anchor to select it and dragging it to a new location. You can also graphically adjust the scope and alarm distance by tapping them and dragging them to a new distance.


If an alarm is generated, you will first want to ensure your vessel is safe. If you feel the alarm was generated unnecessarily, you may want to increase the Alarm Length.