Clearing range
The final tool for the toolbox is clearing ranges. These work just like a clearing bearing by delineating a danger zone. Dartmouth Harbour is well marked and steep-to, so there are few isolated hazards, but we can pretend that Western Blackstone is hard to identify on radar. If it was invisible to radar we would need to create a relationship between it and something that will be visible, like the cliffs. We measure the distance between them and find that it is just less than a cable. If we stay 2 cables off the cliff we will remain in safe water. We can monitor this by setting up a 0.2nm VRM on the radar display. If we keep Blackstone Point outside the 0.2nm circle, we avoid Western Blackstone.
Using a safe distance off an identifiable feature allows you to avoid hazards. Like a clearing bearing, this is a really simple, powerful tool for pilotage.
One nice feature of Wimsey’s setup was the Raymarine display. It allowed those outside to instantly match what was in front of them with the radar picture. As we piloted down the river the channel was well-defined on the radar, and the image on screen started to make sense.
PRESCRIPTION: As we were heading back up the river Sophia said that the day had been a good introduction to radar, but that she still didn’t feel completely confident with it. Sophia is a naturally cautious skipper and her instinct to be wary of using technology which she isn’t completely comfortable with is the correct approach. As she identified, it takes practice to develop good radar skills. But the nice thing about Wimsey’s set-up is that on a quiet day with good visibility she can watch the radar from the helm. This will allow her to build up a bank of experience, getting a feel for what it can do, and also what it can’t, before she needs it in earnest. She will also need to learn how to use the radar for collision avoidance, to complete her skillset.