[Psml] DR Position

[robert sweet]

Doug,

 

Traditional navigation is based on speed through the water since there is no
source of speed over ground.  The derived DR can then be compared with an
actual fix to ascertain and drift due to currents.  GPS provides speed over
ground and actual speed made good.  The ship's log provides distance through
the water not over ground.

 

Bob Sweet

 

From: psml-bounces at usps.org [mailto:psml-bounces at usps.org] On Behalf Of Doug
Thomas
Sent: Saturday, November 22, 2008 10:42 AM
To: aep at mindspring.com
Cc: United States Power Squadrons Mailing List
Subject: [Psml] DR Position

 

When a DR position is being plotted using 60D=ST, is S (speed) the SOG or
the SMG?

 

SOG is taken from the ship's knotmeter.

SMG is computed from the ship's log (ie. log at T1 = 1325 nm, log at T2 =
1350 nm, therefore, D = 25 over that period of time.)

 

 

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