easy calculations and adjustments 57
If your speed is 5.8 knots, how far do you travel in 12 minutes? By moving
the decimal point two places to the right, we know we travel 580 yards in
3 minutes, and 580 × 4 = 2,320 yards.
If your speed is 7.7 knots, how far do you travel in 5 minutes? We know we
travel 770 yards in 3 minutes. Next, fi gure how far you travel in 1 minute: 770
÷ 3 = 256 yards in 1 minute. Multiply by 5 to get your answer: 256 yards × 5
= 1,280 yards.
If you travel 300 yards in 1 minute, what is your speed? First factor how
far you travel in 3 minutes: 300 yards × 3 = 900 yards. By moving the decimal
point two places to the left we get our answer: 9 knots.
If you travel 1,660 yards in 4 minutes, what is your speed? First factor how
far you travel in 1 minute: 1,660 ÷ 4 = 415 yards in 1 minute. Next, factor how
far you travel in 3 minutes: 415 × 3 = 1,245 yards. By moving the decimal place
two places to the left , we know our speed is 12.5 knots (rounded).
This speed is uncorrected for the effects of current or wind. To learn how
to do this, see Chapter 5.SEA-CRET TIP
X Apply the 3-minute rule to fi gure your docking drift rate. At a
speed of 1 knot, your drift rate is 33 yards per minute (100 ÷ 3),
or about 2 feet per second (100 ÷ 60). Use this to judge when to
stop your way and drift to the dock or slip.How to Select and Calibrate a New Compass
Simplicity and reliability are the hallmarks of any great compass. Carry at least
two compasses aboard at all times for safety and peace of mind. If something
happens to your steering compass, the handbearing compass can get you home
in a pinch. You’ll learn more about using this remarkable tool in the next chapter.
Test a compass before you buy it to make sure it meets certain standards.
TESTING A COMPASS BEFORE YOU BUY
- How is the visibility and readability?
Card visibility. Look for a compass with a card diameter of 4 inches
or greater. A card of this size has large, easy-to-read degree markings
that cut down on fatigue and eyestrain. Numbers spaced at 30-degree
intervals are easy to read in a seaway, and you want hash marks at 10- and
5-degree intervals between numbers. Th e compass dome serves as a magnifi er
to further enhance the card markings.