Week 4 20 Estimated Position and Visual Fixing

Week 4 - 20

Estimated Position and Visual Fixing Continued • You will need: • • • Chart RYA 3 Training Almanac Portland Plotter Pencil Dividers

Visual Fixing Exercise – Q 2

Visual Fixing Exercise - Q 3 105 085 T

Visual Fixing Exercise - Q 3 180 T 160 T 105 T 085 T

Working Up an Estimated Position

Plotting an EP We need to know: • Departure Point • Water track (i. e. Course steered corrected for leeway) • Distance sailed through the water • Set and drift of the tide for the period concerned AXE YACHT CLUB

Example Taken from a yacht’s log: Estimate the yacht’s position at 2330. AXE YACHT CLUB

2230/15. 4 2330/19. 9

PLOTTING SYMBOLS 1600 DR (Dead reckoning) 1945 EP (Estimated position) Fix (Observed position) OR 2006 Position line Transferred position line Range / Distance off Depth contour line Water track Ground track Tidal stream AXE YACHT CLUB 20 2117

LEEWAY Wind t o N T) d te t o l P ( ° 0 7 0 e s r u Co Water Track 075°(T) Course Plotted Leeway 5° Water Track = Heading + or - LEEWAY AXE YACHT CLUB

ESTIMATED POSITION WITH LEEWAY Wind ) 0 (T ° 0 7 5° T) ( ° 5 07 090°(T) AXE YACHT CLUB Tidal Stream

Accuracy of the EP Factors to consider:

Fix by Transferred Position Line The running fix

Information required • Bearing to a fixed point, time bearing taken and log reading. • A second bearing to the fixed point taken after a suitable time interval. Ideally, this bearing should be 40 to 50 degrees different from the first bearing. The time of taking this second bearing and the log reading at that time are recorded. • The course steered between taking the two bearings. • The tidal set and drift for the period between taking the two bearings.

Process • Lay off a position line on the first bearing from the fixed object. • From any point on this line, construct an EP using the water track, distance run and tidal information. • Transfer the first bearing to give a transferred position line through this EP. • Lay off the second bearing from the fixed object. • Intersection of this second line with the transferred position line gives the “fix” at the time the second bearing was taken.

Running Fix Example From a Power Boat’s Log Time Log Co Wind L’way Narrative 0940 25. 3 044 T W 3 Steven’s Rock Lighthouse bears 085 T 1010 29. 8 044 T W 3 Steven’s Rock Lighthouse bears 214 T Tide stream between 0940 and 1010 = 094 T / 2. 4 knots. What is the boat’s position at 1010?

The Chartwork

The Chartwork

One to try! Take variation as 6 W and use the deviation curve in the Training Almanac Taken from a yacht’s log. Time Log Co Wind L’way Narrative 1500 27. 7 265 C NE 3 - South Head Lt bears 342 M 1530 31. 2 265 C NE 3/4 - South Head Lt now bears 068 M (Tidal stream 1500 -1530 is 125 T / 1. 2 knots) Find the yacht’s position at 1530.