The World's Most Advanced Sailing Education and Sailing Certifications

Known Rate and Direction calculations

Forum - Coastal Navigation - Known Rate and Direction calculations
Module Content - Sea Talks4
avatar
Student
Paul Schwendeman
Wexford, PA, USA
Skipper (small keelboat) Level I
Status: Sailor
Qualified days: 16
Known Rate and Direction calculations
Posted 2016, Jan 21 22:49
I've very confused in this section! Why is a curve used at the end of the vector line and not a straight line? How is the length of the vector line determined? Do I use the time/speed formula, determine distance over one hour and use latitude scale on left side of chart? I get the DR course line and the COG line but can't grasp the vector information and where to place it.
Add reply
2 0

Replies

avatar
Administrator
Grant Headifen
Reply 2016, Jan 22 15:31
The curve is an arc scribed using dividers to create the length of the vector. The length is determined by one hour of travel time or one hour of current flow time eg 3 knots in 1 hour is 3 nm. The length is gained from latitude on left or right of chart. The DR line plus the current vector line (in the direction of the current) all over 1 hour create the COG line. At the end of the DR line start the current vector line. The graphic sum of those vectors create the COG.
2 0
avatar
Student
Jay Herrmann
Dillon, CO, USA
Crew Level IV
Status: Sailor
Qualified days: 111
Reply 2016, Feb 06 00:16
Glad to have found Sea Talk. Lots of questions about this module. My first question is answered above. It would be great to see that information in the curriculum A working example calls for use of RYA Chart 3. Did I miss that as an item I needed for this course?
5 0
1 - 2 of 2 replys

Add reply

* - required fields

Please signin first
Add your reply in a positive and constructive manner and tone. Be as specific and clear as possible. Other students will vote your reply up or down depending on its usefulness the clarity. Your comments are always editable.