Cardinal and special-purpose buoys, and reading a chart

Mei is thirty-nine, out on a sunny afternoon in her bowrider with her sister. She's followed the line on her chartplotter all day. Then the screen goes black. At that same moment, she spots a white buoy ahead with an orange diamond on it. She has no idea what it means, and her map has just disappeared.

So here's the question. What is that buoy telling her? And what does she steer by now?

Start with the white buoys. In Canada's buoy system, as Transport Canada's Safe Boating Guide lays it out, white buoys with orange symbols are special-purpose buoys, and the symbol is the message. An orange diamond means hazard, such as a rock or shoal, with details inside it. An orange circle is a control buoy, and the rule inside, like a speed limit, applies. An orange square gives information, such as a marina or campsite.

A keep-out buoy has an orange diamond with a cross inside it, plus orange bands. Swimming buoys mark the outer edge of a swimming area, and they may not be on your chart. You'll also meet cautionary, anchorage, diving and mooring buoys. A mooring buoy is the one you're allowed to tie up to. If lit, special-purpose buoys show yellow lights.

Then there are cardinal buoys, yellow and black, placed around a danger. Each is named north, east, south or west for the side where the safe water is. The clue is on top, two black cones, and the points tell you where to find safe water. On a north buoy, both point up. On a south buoy, both point down. East cones sit base to base, and west cones point to point.

Now the chart. The Canadian Hydrographic Service publishes a free booklet called Chart Number One. It's the key to the symbols, abbreviations and terms on its charts. Depths are measured from a reference level called chart datum. And Transport Canada's guide says a marine GPS gives your position to within about ten metres, and advises keeping charts aboard in case it fails.

One legal duty. Under the Canada Shipping Act, if your boat damages or moves a buoy, you report it to the Coast Guard without delay. You also report a buoy that's missing, out of position or not working, and any hazard that isn't on the chart.

On the water. My plotter is a wonderful thing, and I still keep the paper chart for my stretch of river on the seat beside me, folded to where I am. When a screen dies, I don't want to be unfolding a chart in the wind. The practice charts the Hydrographic Service gives away are great for learning, but they're not for navigating.

Let's change one fact. Instead of the white buoy, Mei sees a yellow and black buoy with two black cones on top, both pointing down. That's a south cardinal, so the safe water lies to the south of it. She slows down, works out which way south is, and passes on that side.

The mistake boaters make is reading a cardinal buoy backwards. A north buoy doesn't mean the danger is to the north. It means the safe water is. The other mistake is trusting one screen with everything.

Here's the rule, in one breath. White and orange buoys carry their message in the symbol, cardinal cones point to safe water, and a paper chart backs up every screen.

This week, download Chart Number One for free, and find five symbols you'd meet on your usual route. Next time, a new module, laws on the water, starting with drinking, speed near shore, and your wake.