We were intrigued with descriptions of Sperm Bay from a local boat, and even though the detailedCanadian chart for the area contains no soundings, we decide to give it a look. Conditions are ideal. We are half way through a rising tide (so we have the tide to float us off any mistakes), and winds are calm.

This will make an interesting contrast to the piloting approach we’ve used entering Flamingo Inlet.

In the olden days we’d launch the dinghy first, and check the anchorage with a portable depth sounder. Now that we’ve got SONAR on board we only use the the dinghy in really tight spots (and our definition of "tight" has changed).

The following series of photos are taken of the SONAR (left) and radar (right) screens, to give you a feel for how the data develops. For the most part we are moving on one engine running at idle. This engine is often out of gear as we stop to assess the data coming back to us from the SONAR. The key in situations like this is to take it slow and easy. We like using a speed which allows plenty of time to think about what we’re seeing, both electronically and with our senses.

In the next series of images the SONAR range is set to 620 feet (190m) and the radar is on .25 nautical mile (with each range ring equal to a 300 foot/92m radius). Above, we are about to enter the entrance to Sperm Bay. The SONAR shows the edges of the bay while the radar looks through the entrance. Note that with the angle the SONAR is set at, 4 degrees, at the edge of the SONAR screen we will see returns from targets 41 feet (12.5m) deep.

The white line behind the triangle on the SONAR represents our track. There is also a track on the radar. We can always follow these tracks back out if the situation gets too tight for comfort.

We’ve started to move into the entrance, keeping ourselves centered on the radar image. The SONAR is clear ahead.

Just a little further into the entrance and we are starting to see a target ahead and to starboard of our course on the SONAR. This could be kelp, current or temperature shear, or something that would scrape our bottom paint. A slight alteration of course to port has us aiming towards clear water.

We’re inside the entrance of the cove now. What looked like it might be an obstruction in the previous photo you can now see in better detail, several hundred feet (60m) to starboard. This is indeed a shallow spot. There’s plenty of space in the channel to proceed, but directly ahead there is a shoal or reef. However, the way is open to port, and we decide to proceed.

We can see here that we have to work our way between the obstruction to starboard and what is starting to appear to port as a reef extension.

We’re now tucked into the small basin, behind the island shown at the bottom of the radar. The SONAR is now set on a range of 460 feet (141m), and we are looking at the image all the way around the boat (past images were looking just ahead). The dotted circle on the SONAR represents a circle of 212 feet (65m) in diameter. Radar is on 1/8th nautical mile with range rings having a radius of 150 feet (45m).

Water depth at half tide if 46 feet (14m). Assuming scope of 3-1 – OK with our big ROCNA anchor – we need at least 200 feet (60m) to swing when allowing for our hull length. There is not enough room, unless we shorten up on the scope, which we are not willing to do in this part of the world, even in midsummer. While the weather scenario looks benign, we would not sleep well worrying that we, or the Canadian weather forecasters, had missed something.

We decide to retrace our path back out into Flamingo Inlet and move to a larger, albeit less aesthetic, anchorage.