[C320-list] Boat Speed

[belairlk at aim.com]

I totally ignore the speed instrument, and rely on GPS sog  (speed over ground) readout on chartplotter at the helm which I understand IS accurate (unless satellite changes orbit or you're suddenly over the Marianas Trench).  Wonder how many 320's have GPS at this time?
 
Len
Aqua 5 #1070
 
 
 
 
 
-----Original Message-----
From: Walter burnett <selkie2003 at yahoo.com>
To: C320-List at catalina320.com
Sent: Tue, 25 Apr 2006 14:56:23 -0700 (PDT)
Subject: [C320-list] Boat Speed


All,
   
  It occurs to me the many variations in reported boat speed is likely due to 
variations in the speed sensor calibration, or lack thereof.  The only accurate 
way to calibrate the boat speed sensor is by timing multiple passes ata a 
constant speed through a measured course in slack water and opposite directions.  
Average the runs, calculate the speed and compare it to the readout for a 
correction factor to enter into the display. The more and longer the runs, the 
more accurate the calibration.
   
  In my experience the speedo out of the box can be off as much as 25%.  I 
suspect most boat dealers don't make any effort to calibrate the instruments 
before delivery and many skippers either don't know or don't bother. 
   
  Walter
  Selkie #887

        
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