Bow Beam Bearings – Answers to May Question

You are cruising about 2 nm south off the south shore of Martha’s Vineyard in the vicinity of Tisbury Great Pond on a course of 262º True. Your boat speed is 5 kts. At 0930 you observe the Radar Tower on Martha’s Vineyard at 045º relative.
What is the true bearing to the Radar Tower? 307º True
What will be the true bearing when the Radar Tower is directly abeam? 352º True
At 1001 the Radar Tower is directly abeam. Remember that the distance traveled using your DST formula equals the distance off the object at the time of the second LOP.
What was the distance traveled? 2.6 nm
What is your 1001 position? 41º 18.7′ N – 070º 43.7 W
What is the charted water depth? 60 feet

Step by Step Explanation

  1. Plot your course line of 262º true approximately 2 miles south of Tisbury Great pond.
  2. Since the problem indicates that you observe the Radar Tower at 045º relative you must add that to your true course to find the True direction of the Radar Tower.
    (262 + 45 = 307)
  3. The true bearing when abeam will be when the Radar Tower is at 090º relative. Again add to your true course direction.
    (262 + 90 = 352)

  4. Calculate the distance traveled between 0930 and 1001.
    (.51 hrs X 5 kts = 2.6 nm)

  5. Plot a LOP line of 352º to the Radar Tower.

  6. Using your dividers on the latitude scale find the distance of 2.6 nm.

  7. Measure this distance from the Radar Tower along the LOP. Where this distance off the Tower crosses your LOP is your 1001 position.

  8. Check the depth contour line on your chart to see that you are on the 60′ contour.


Early days of fishing and wakeboarding boats. These days a little more relaxing and sailing time, mostly on catamarans. Still too poor be a yacht man.

Leave a Reply

Your email address will not be published. Required fields are marked *