June 16, 2009

Honoring the hockey puck

ONE OF MY MOST VALUABLE navigation tools is the little hand-bearing (“hockey puck”)compass I wear on a cord around my neck. It’s an essential part of chart navigation, of course, because it’s what you use to take magnetic bearings of prominent features on land. Two or more of those bearings allow you to plot your position on the chart.

But the hockey puck compass is also valuable if you navigate by GPS. Let’s presume you’re heading for an anchorage on Flybutton Island, one of many in the Trousers Archipelago. As usual, with islands overlapping, covered with pine trees, and all looking alike, you can’t see any obvious entrance to Zip-Up Cove on Flybutton Island.

However, you have programmed a waypoint into your GPS; and now your GPS is telling you to steer a course of 250 degrees magnetic to Zip-Up Cove. All fine and good, but because of currents and leeway, your main steering compass is not going to take you to Zip-Up Cove while you steer 250 degrees. If you’re beating, your boat will be making leeway, so she won’t be going where she’s pointing. And if you’re in a current, as you mostly are around here, you have to allow for being set sideways.

An experienced navigator knows how to compensate for all this, naturally, and your GPS will tell you how much you’re going off course. But there’s a simple trick that’s very reassuring to Nervous Nellies: When the GPS says the direction to your destination waypoint is 250 degrees, get out your hand bearing compass and sight through it until it shows 250 degrees. Now you are looking at the actual place on land that you are aiming for. Make a note of any landmarks you can see, such as a tower or a tall tree, or a mountain with a cleft.

When you can actually see a place to aim for like this it’s a great help with the steering. You still need to compensate for being set off course, but it’s reassuring to have the GPS course confirmed by your hand bearing compass.

Another thing — if you stand in the cockpit to take your bearing, you’re usually well away from any ferrous metals and current-bearing wires, so your hockey puck compass is not affected by the ship’s deviation, and will show a true magnetic course. (If you wear glasses, just make sure the frames aren’t magnetic.)

As you probably know, there are many other uses for this little compass; too many to explore in this limited space, but they include the ability to warn you of impending collisions with other vessels, and to reveal the deviation of your main steering compass. Your hockey puck can also help you stay clear of charted (but not visible) underwater dangers, and by giving you two quick bearings, it can tell you how far you are off a prominent landmark. In addition, it will tell you in an instant if your anchor is dragging.

Furthermore, if you take it ashore with you, it will help you find your way back to the boat in a dark anchorage, or in thick fog. And so on. For 150 bucks or less, it’s a great safety aid for any sailor and a particularly valuable tool for the navigator.

Today’s Thought
Those who travel heedlessly from place to place, observing only their distance from each other, and attending only to their accommodation at the inn each night, set out fools, and will certainly remain so.
—Lord Chesterfield

“Who was that eye doctor I saw you with in Alaska?”
“That was no eye doctor. That was an optical Aleutian.”

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