118 



UNITED STATES COAST GUARD 



What effect does the material com- 

 posing an object have on its being de- 

 tected by radar? 



How could you identify low flying air- 

 craft appearing on the radar scope? 



What limits the effective range of 

 radar? 



Describe briefly the essential parts of 

 a radar set. 



What is the effect of a radar reflector 

 on a buoy? 



Is a bearing obtained through use of 

 radar or visually preferable? why? 



In using radar to obtain navigational 

 positions, which should be more ac- 

 curate : 



(a) A fix obtained by cross-bearing 

 of two objects. 



(b) The intersection of the arcs ob- 

 tained using the ranges from the objects 

 as radii. 



Explain your answer. 



Do atmospheric conditions affect the 

 range at which objects may be dis- 

 cerned by radar? State the reasons for 

 your answer. 



What safety precautions must be 

 taken when examining or working on 

 the intei-ior of a radar set? 



Navigating in ice, how may areas of 

 clear water be distinguished on the 

 PPI scope? What are the limitations on 

 the effectiveness of radar in detecting 

 ice bergs and growlers? 



Define : 



(a) Relative movement; 



(b) Relative speed ; 



(c) Relative distance. 



In each of the following cases, give 

 the approximate direction and rate at 

 which the pip would move on your PPI 

 scope : 



(a) If your vessel, while proceed- 

 ing North at 15 knots, observed by 

 radar a stationary object. 



(b) If your vessel, while proceed- 

 ing East at 10 knots, observed by radar 

 a vessel proceeding West at 10 knots. 



(c) If your vessel, while proceed- 

 ing South at 10 knots, observed by 

 radar a vessel proceeding South at 10 

 knots. 



What does a sudden increase or 

 decrease of the signal strength of an- 

 other vessel's pip on the PPI scope usu- 

 ally denote when the vessel observed on 

 the PPI scope is close to your vessel? 



What factors aboard ship would 

 cause blind sectors on the PPI scope? 



Explain in your own words how the 

 course and speed of another vessel is 

 determined by ranges and bearing 

 taken by an observer on a moving ves- 

 sel. 



Your vessel is on course 230* True 

 at a speed of 8 knots. 



At 0800, a vessel is observed on the 

 PPI scope bearing 290" True at a dis- 

 tance of 7.6 miles. 



At 0815, the vessel is observed bear- 

 ing 283° at a distance of 6.0 miles. 



At 0830, the vessel is observed bear- 

 ing 273° at a distance of 4.6 miles. 



(a) Assuming that both your ves- 

 sel and the vessel observed maintain 

 course and speed, determine the dis- 

 tance between your vessel and the ves- 

 sel obsei-ved at their closest point of 

 approach. 



(b) Determine the course and 

 speed of the vessel observed. 



(c) Determine the time of the 

 closest point of approach. 



Your vessel is on course 135° True at 

 a speed of 9 knots. 



At 0028, a vessel is observed on the 

 PPI scope bearing 110° True at a dis- 

 tance of 10 miles. 



At 0032, the vessel is observed bear- 

 ing 109° at a distance of 9 miles. 



At 0036, the vessel is observed bear- 

 ing 107°. 5 at a distance of 8 miles. 



(a) Assuming that both your ves- 

 sel and the vessel observed maintain 

 course and speed, determine the dis- 

 tance between your vessel and the ves- 

 sel observed at their closest point of 

 approach. 



(b) Determine the course and 

 speed of the vessel observed. 



(c) Determine the time of closest 

 point of approach. 



Your vessel is on course 060° True 

 at a speed of 8 knots. 



At 1500, a vessel is observed on the 

 PPI scope bearing 080° True at a dis- 

 tance of 7 miles. 



At 1508, the vessel is observed bear- 

 ing 080° Ti-ue at a distance of 6 miles. 



(a) Determine the course and 

 speed of the vessel observed. 



(b) Determine that course to 

 which to alter at 1512 which will en- 

 able you to pass the observed vessel at 

 a distance of 3 miles on your port side. 



Your vessel is on course 140° True at 

 a speed of 6 knots. 



At 1200, a vessel is observed on the 

 PPI scope bearing 200° True at a dis- 

 tance of 5 miles. 



At 1206, the vessel is observed bear- 

 ing 200° True at a distance of 4 miles. 



At 1212, the vessel is observed bear- 

 ing 200° True at a distance of 3 miles, 

 (a) What would be the effect of 

 altering your course to 080°? Explain 

 in full. 



