We’ve mentioned in the past the value of having a fish finder (fathometer) as a back up position fixing device and navigation quality control tool. Here is a great example of how this works approaching the entrance to the Yellow Banks from Exuma Sound in the Bahamas.

As you can see from the chart above, there is an abrupt change in depth.

Our fish finder/sonar is set to record depth trends when we are not using the sonar. The trace here is taken at the position shown on the chart (depths on the chart are in meters).

If you are cruising in deep water and see this occur, you know for sure to stop and figure out what is going on, before that depth trace gets any shallower!

We heard various stories about how difficult Yellow Banks is to cross. However, we have the sun behind us, so the eyeball navigation is working well.

The photo above and below are taken in 12 feet (3.8m) of water.

This coral head has about three to four feet (0.9 to 1.2m) of water over it.

If it starts to cloud over, then the ability to eyeball your way around the coral heads is lost.

In our case we were lucky in that the sky ahead cleared, but continued to develop behind us.

Given our shallow draft, just five feet at the bottom of the keel (1.5m), had we lost visibility we probably would have proceeded slowly since we could clear most of the heads. But the option always existed of anchoring until visibility improved.