88 



UNITED STATES COAST GUARD 



How may you : 



(a) Estimate the bearing of the 

 center of a tropical cyclone? 



(b) Estimate the probable path of 

 a storm ? 



Hove to in the Northern Hemisphere 

 under tropical cyclone conditions, the 

 barometer is falling and the wind shift- 

 ing clockwise. What is the vessel's prob- 

 able position relative to the center of 

 the storm and what action should be 

 taken if possible to avoid the center of 

 the storm? 



State the precautions that should be 

 taken in the event it becomes necessary 

 to ride out a tropical cyclone at an an- 

 chorage. 



What is one method of predicting the 

 probable area within which a tropical 

 cyclone can be expected to move within 

 24 hours from the time at which it is 

 reported? 



What is the "intertropic convergence 

 zone"? 



Your vessel is proceeding toward a 

 stationary thunderstomn at 15 knots. If 

 you saw a flash of lightning and 10 

 seconds later heard thunder, how long 

 would it take before you entered the 

 storm? 



How would you estimate the prob- 

 ability of ericountering fog on an ocean 

 passage? 



How is the information concerning 

 the direction and velocity of ocean cur- 

 rents obtained for Pilot Charts and 

 Current Charts of the oceans? 



In using information concerning cur- 

 rent from a Pilot Chart or Current 

 Chart, what consideration should be 

 borne in mind with regard to possible 

 differences between the actual current 

 experienced and that shown on the 

 chart? 



Under certain conditions in the 

 Northern Hemisphere it may be as- 

 sumed that the current sets 30° to the 

 right of the direction of which it is 

 driven by the wind and its velocity is 

 2 percent of the wind velocity. 



(a) Basing your answer on the 

 foregoing statement, estimate the direc- 

 tion and the velocity of the current if 

 the wind is from the west at 50 knots. 



(b) Using direction and velocity of 

 current estimated in (a) , find the course 

 to steer your vessel to make good a 

 course of 030° if the speed of your 

 vessel is 10 knots. To solve this prob- 

 lem, consider current only, disregarding 

 any other factors that might be in- 

 volved. 



Currents shown on Pilot Charts and 

 Current Atlases are "resultant" cur- 

 rents. 



(a) What is the meaning of the 

 term "resultant"? 



(b) How would you assess the 

 probability of your vessel encountering 

 the particular conditions indicated by 

 the current information on the chart? 



The distance between two ports on 

 the Great Circle track is 3,000 miles, but 

 the track traverses areas where adverse 

 currents whose average velocity is 1 

 knot can be anticipated. An alternate, 

 mercator course of 3,400 miles in length 

 between the ports traverses areas where 

 a favorable current averaging 1 knot 

 can be expected. 



With the length of time required for 

 the passage as the only consideration, 

 determine which track is preferable for: 



(a) A vessel whose speed is 10 

 knots. 



(b) A vessel whose speed is 15 

 knots. 



(c) A vessel whose speed is 20 

 knots. 



20. NAUTICAL ASTRONOMY AND NAVIGATION DEFINITIONS 



The earth actually rotates 366^4 

 times in a year, but the sun crosses 

 the meridian only 365 times, making the 

 year consist of 365^/4 solar days. What 

 causes the apparent loss of one rotation? 



At what rate per hour is Greenwich 

 Observatory, in Latitude 51°-28'.6 

 North, being carried around the earth's 



State two of the three factors which 

 cause apparent time to differ from 

 mean time. 



How must the lines of position of 

 bodies with altitude (Ho) from 86° to 



90° be plotted? How are such position 

 lines advanced? 



Distinguish between superior and in- 

 ferior planets. 



Define precession of the equinoxes. 



What is right ascension? 



What is the ecliptic? 



Define : 



(a) Aphelion 



(b) Perihelion 



(c) Apogee 



(d) Perigee 

 What is precession? 



