7 STEPS TO PLOTTING A RUNNING FIX

7 STEPS TO PLOTTING A RUNNING FIX

If you can maintain a consistent boat speed AND an unwavering boat heading, then the running fix can get you a better position fix than just using your dead reckoning positions. There may be a current pushing you off course, or the wind may be causing you to drift so you’re never going to be where your DR says you should be.  When taking bearings, it’s best to use landmarks that are fixed, like a really obvious tower or lighthouse. Don’t use another moving boat!

There is sure to be at least one of these kinds of questions on any Coastal Navigation Exam, and it behooves you to practice it often.  When I was taking my American Sailing Association level 105 with the Maryland School of Sailing, this kind of question really tripped-up the students. It wasn’t until I just gave in, and instead of understanding the why of the geometry, I just decided to memorize the how. So, I wrote myself a step-by-step cheat-sheet of procedure and just performed the answer like a choreographed dance using rulers, pencil and dividers instead of feet, arms and hips!

Hopefully this little step by step, 5,6,7,8 will prevent you from breaking out into a cold sweat every time you come across a Running Fix question and help put the sparkle back in your navigation plotting “jazz hands”!

The video below works through the practice question using the Training Chart 1210Tr. The diagrams below are just references and do not necessarily relate to the practice question, but it’s pretty similar!

The solution in the video and here, assumes you already know how to use your plotting tools and that you already have some basic techniques under your belt. If you don’t know how to do the following then, you probably aren’t ready to tackle this one!

Know How To:
  • calculate the magnetic variation according to the year of the chart and the year in the question
  • plot course heading
  • plot dead reckoning positions
  • plot bearing LOP (lines of position)
  • find the latitude and longitude of a position
  • use a deviation table
  • calculate T-V-M-D-C

Read the sample, practice question below then follow the 7 Steps for Success! 

At 0800 on September 25, 2002 you depart the W Or “A” Fl 4 sec BELL buoy located about 6nm to the SE of Point Judith. You set a course of 313° psc at 5.2 knots. At 0900 you take a visual bearing of 027° on Point Judith Light. At 0930 you take a second bearing of 071° psc on Point Judith Light. What is your 0930 position?

*question is from Capt. Tom Tursi, Maryland School of Sailing workbook. All diagrams by boatLUV.

STEP 1

Plot the Course Line (COG) – ship’s heading in “True”​

plot the Course Line

STEP 2

Plot the Dead Reckoning positions (DR) along the Course Line (dot with half circle) – calculated for distance traveled for each Bearing Sight time. Distance = Time X Boat Speed​

plot the dead reckoning positions

STEP 3

Plot Bearing 1 Line of Position (LOP) & Bearing 2 LOP – label them with the times they were sighted​

plot bearing lines of position

STEP 4

Plot the Average Course Line (ACL) – line up parallel ruler with COG and slide it over to cross B1 LOP & B2 LOP

plot the Average Course Line

STEP 5

Plot DR position of the time of second sighting on ACL – space dividers to width of first and second DR positions on COG, place one end of the divider where ACL crosses B1 LOP then mark the ACL with the other end.​

measure DR distance on ACL

STEP 6

Plot the Advanced Line of Position (ALOP) by lining up the parallel ruler to the B1 LOP and sliding it over to the mark you just made on the ACL.  Label this ALOP with the two times the Bearings were taken i.e ALOP 0900 – 0930

slide Adjusted Course Line over to hatch

STEP 7

Your Running Fix Position is where the ALOP crosses the B2 LOP.  Mark this with a dot and a circle and label it RF & the time of the second Bearing. i.e. RF 0930­

running fix has a dot and a circle

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