SailNet Community - View Single Post - GPS determined speed
View Single Post
post #4 of Old 08-12-2019
pdqaltair
Senior Member
 
pdqaltair's Avatar
 
Join Date: Nov 2008
Location: Deale, MD
Posts: 3,724
Thanks: 4
Thanked 131 Times in 129 Posts
Rep Power: 12
 
Re: GPS determined speed

Really, it is a simple matter of understanding how GPS works. It calculates where you are, and that calculation has some error, on the order of 3 meters. So obviously, there will be some variation in instantaneous speed. In fact, in order to be relatively certain of 0.1 knot accuracy (1%) you would need to average ~ 1000 feet. It does much better than that, for a number of reasons, but over just a few seconds there can easily be a few tenths disagreement.

We expect miracles. 0.1 knot based on a time delay from a satellite. Not happening. I though GPS was a miracle when it just gave lon/lat within a few hundred feet.

Writing full-time since 2014
Author--Rigging Modern Anchors

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

"Keeping a Cruising Boat for Peanuts"
"Faster Cruising for the Coastal Sailor"
"Singlehanded Sailing for the Coastal Sailor"
pdqaltair is offline  
 
 
For the best viewing experience please update your browser to Google Chrome