SailNet Community - View Single Post - GPS vs Knotmeter
View Single Post
  #2  
Old 04-28-2003
Silmaril Silmaril is offline
Senior Member
 
Join Date: Feb 2003
Location: New England USA
Posts: 261
Thanks: 0
Thanked 1 Time in 1 Post
Rep Power: 12
Silmaril is on a distinguished road
GPS vs Knotmeter

While a GPS will give you an average speed reading, it is over the bottom speed and not through the water speed. This is most significant when sailing in an area with a swift measurable current, such as a river, an area subject to tidal currents, or the ocean currents. It is totally unacceptable as a method to trim for speed, as you suggested, as it cannot react quickly enough and may be off-set by currents.

Same can be said of substituting a GPS for a helms compass. Be aware that you may be reading "True" courses, rather than magnetic courses. And also be aware that is is showing you your "Reading" or course to a particular nav point, not the direction you are pointing!

GPS are wonderful devices, but you have to use them for what they were intended for, a navigational aid. And then as a supplement to other forms of navigation. A person who relies exclusively on his "GPS/Map-color Model 4554" for navigation will have a rude awakening the first time the power is down on the batteries.

Can a GPS be used as a temporary fill-in while you save for your knot meter? Of course it can, but remember it''s limitation on showing it''s specific type of data.
Reply With Quote Share with Facebook