[C320-list] Boat Speed

[Adam Weiner]

Why wouldn't it be accurate over the Marian's Trench?

Adam

-----Original Message-----
From: C320-List-bounces at catalina320.com
[mailto:C320-List-bounces at catalina320.com] On Behalf Of belairlk at aim.com
Sent: Tuesday, April 25, 2006 2:09 PM
To: C320-List at catalina320.com
Subject: Re: [C320-list] Boat Speed


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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