piloting tips and techniques 87
Distance off (DO): Th e distance you need to stay off the shoal to clear
it safely.
Distance ahead (DA): How far ahead the shoal lies from your current
location.
- Determine the safe side (left or right) on which to pass the shoal
- Decide on the required distance off (DO) the shoal to clear it safely
- Measure how far ahead the shoal lies from your present location (DA)
- Multiply 60 by the DO
- Divide by DA.
Apply the result using one of these two rules:
If the safe side is to the left of the shoal, subtract the result from the
trackline and steer that course.
If the safe side is to the right of the shoal, add the result to the trackline
and steer that course.
Our course is 045 degrees magnetic. The chart indicates a dangerous shoal
off our starboard bow 2 miles ahead (DA). The safe side is to the right of the
shoal, and we need to stay 1 mile off (DO) the shoal to clear it safely. How many
degrees do we need to turn to starboard to clear the shoal by 1 mile?
Multiply 60 by the DO and divide by the DA. Our calculation would be:
(60 × 1)/2 = 30 degrees.
Since the safe side is to the right of the shoal, we add the correction: 045 degrees
magnetic + 30 degrees = 075 degrees magnetic.SEA-CRET TIP
X Always use the Rule of 60 with caution. It does not tell you the effect
of current or leeway once you change course. Calculate the course
alteration and then estimate the effect of current (see Chapter 5).
Sailing vessels may also need to estimate leeway if the new course
results in heading up.Depth Contour Secrets
With just a fathometer corrected for tide and transducer location, you can
use depth contour curves to estimate your speed and position. Look at any
nautical chart and you’ll see thin, black lines. Starting along the shore, they
closely match the profile of the shoreline. Farther away, these lines take on
every shape under the sun—from gentle curves to crazy, out-of-control