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Sailing a a course perpendicular to the course of the storm will NOT
achieve the
maximum possible CPA unless the storm is traveling at the same speed as
you.
This type of storm avoidance question is a relative motion plot, easily
accomplished on a maneuvering board or a plotting sheet. However, it can
also be
done on a chart.

-- Plot your vessel (at the center if using a maneuvering board).
-- Plot the position of the storm center.
-- Plot the storm�s speed vector (a line representing its direction and
speed. In
your second example, 265T for 22 miles). This line is drawn beginning
from your
current location.

-- From the outer end of that line, draw a line tangent to the 12 knot
speed circle
(a circle with a radius of 12 nm with its center at your location).

-- From your position, draw draw a perpendicular to this tangent line.
This is the
direction you need to travel to achieve maximum CPA.

-- Extend that line in the opposite direction, until it crosses the
course of the
hurricane. That point represents the location of the hurricane (assuming
course
and speed remain the same) at the time of CPA. From there, calculate how
long it
will take the storm to reach that point, and you can establish the time
'til
CPA.

--
Carl Herzog
Editor, Reed's Nautical Almanacs

www.reedsalmanac.com
carlzog@reedsalmanac.com
-------------------------------------------
120 Fulton Street
Boston, MA 02109
Ph# (617) 227-1300
Fax# (617) 268-5905

   

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