June 19, 2012

The useful hockey puck

ONE OF THE MOST VALUABLE navigation tools here in the Pacific Northwest is the little hand bearing (“hockey puck”) compass you can wear on a cord around your 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 if 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
The sea never changes and its works, for all the talk of men, are wrapped in mystery.
— Joseph Conrad

“Waiter, there’s a fly in my soup.”
(2)“Don’t worry, sir, he’ll sink when he’s dead.”

(Drop by every Monday, Wednesday, Friday for a new Mainly about Boats column.)


Anonymous said...

How did I not know of this magic? Can anybody recommend a good one?

Laugh at life said...

Apologies, I am not a sailor nor do I have a relevant comment for this post. I am seeking the author of an article called Kent at Sea: The Ill Fated TID 97. The author's name was John Vigor and I wondered if you are the same man?

John Vigor said...

Anon: Any decent marine store can help you. Here's a good compass from West Marine:

John V.

John Vigor said...

Hi Laugh at Life:

I used to write for Kent Life magazine way back in the 60s and contributed to their Kent at Sea series. I don't recall anything to do with TID 97, but if you give me more details about the article I might manage some glim recollection. Not many people called John Vigor.

John V.