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Search took 0.00 seconds. Search: Posts Made By: transmitterdan
Forum: General Sailing Forum 22-03-2015, 12:34
Replies: 442
Views: 38,404
Posted By transmitterdan
Re: Speed Through GPS Versus Old Fashioned Paddle Log

The only reason the debate over GPS speed came up is someone complained that GPS speed update is "too slow" because it has to wait to get two or more position fixes to calculate speed. This is...
Forum: General Sailing Forum 19-03-2015, 17:02
Replies: 442
Views: 38,404
Posted By transmitterdan
Speed Through GPS Versus Old Fashioned Paddle Log

These days a boat can have 5-6 GPS receivers without trying hard. It's hard not to have that many.
Forum: General Sailing Forum 19-03-2015, 14:19
Replies: 442
Views: 38,404
Posted By transmitterdan
Re: Speed Through GPS Versus Old Fashioned Paddle Log

Dockhead,

I get how you use an estimate of STW to plan a course. And I get that you will adjust your future CTS calculations based on your previous STW by assuming that in the future the STW will...
Forum: General Sailing Forum 19-03-2015, 13:47
Replies: 442
Views: 38,404
Posted By transmitterdan
Re: Speed Through GPS Versus Old Fashioned Paddle Log

It is powering with no current and no heel. On our boat the sensor is pretty far below the waterline.
Forum: General Sailing Forum 19-03-2015, 09:46
Replies: 442
Views: 38,404
Posted By transmitterdan
Re: Speed Through GPS Versus Old Fashioned Paddle Log

I have done some calibration curves of my Raymarine paddle wheel. At 6.5 knots it is accurate +/-0.2 knots. At 3 knots it reads high by 1 knot. At 1 knot it reads zero. There is no calibration...
Forum: General Sailing Forum 19-03-2015, 05:51
Replies: 442
Views: 38,404
Posted By transmitterdan
Re: Speed Through GPS Versus Old Fashioned Paddle Log

Ok, I get the "guessing where the tide will take us" scenario. Sorry for being dense. But I agree with Dave that in all this discussion no one has explained how STW would affect their calculations or...
Forum: General Sailing Forum 18-03-2015, 14:51
Replies: 442
Views: 38,404
Posted By transmitterdan
Re: Speed Through GPS Versus Old Fashioned Paddle Log

Ok, I'll give my answer to the problem (which could be wrong). I think the GPS will show throughout the passage that the due north heading gives the best VMG. All other headings will result in a...
Forum: General Sailing Forum 18-03-2015, 14:48
Replies: 442
Views: 38,404
Posted By transmitterdan
Re: Speed Through GPS Versus Old Fashioned Paddle Log

But if he had put that route into his GPS before he left he could tell in an instant whether or not he was following his plan.

Here is an interesting question:

Assume the example of...
Forum: General Sailing Forum 18-03-2015, 08:47
Replies: 442
Views: 38,404
Posted By transmitterdan
Re: Speed Through GPS Versus Old Fashioned Paddle Log

Dockhead,

It depends on how you have made your voyage plan. If you estimate set and drift and plot a course then that can be easily transferred to a planned route over ground. If you find that you...
Forum: General Sailing Forum 17-03-2015, 13:45
Replies: 442
Views: 38,404
Posted By transmitterdan
Re: Speed Through GPS Versus Old Fashioned Paddle Log

^+1

Ericson 38 is exactly right. I would just add for clarity that with GPS speed and position is not necessary to do all those set and drift calculations to know your exact position and VMG...
Forum: General Sailing Forum 16-03-2015, 17:15
Replies: 442
Views: 38,404
Posted By transmitterdan
Re: Speed Through GPS Versus Old Fashioned Paddle Log

Almost any method of measuring speed using Doppler is more accurate than a paddle wheel. And Doppler speed measurement is very fast. So if you want accuracy and fast updating then Doppler is the way...
Forum: General Sailing Forum 15-03-2015, 04:53
Replies: 442
Views: 38,404
Posted By transmitterdan
Re: speed through GPS versus old fashioned Paddle Log

Misah give up...
Forum: General Sailing Forum 14-03-2015, 09:22
Replies: 442
Views: 38,404
Posted By transmitterdan
Re: speed through GPS versus old fashioned Paddle Log

GPS calculated velocity is extremely accurate at pretty much any speed. Much more accurate in terms of velocity relative to the ground than a paddle wheel knot log.

You can try a simple experiment...
Forum: General Sailing Forum 14-03-2015, 07:43
Replies: 442
Views: 38,404
Posted By transmitterdan
Re: speed through GPS versus old fashioned Paddle Log

Doug, I think all GPS receivers you can buy today measure speed using Doppler effect. I have no way to verify that but I think it's a safe assumption. All GPS receivers measure Dopper shift so it's...
Forum: General Sailing Forum 14-03-2015, 06:42
Replies: 442
Views: 38,404
Posted By transmitterdan
Re: speed through GPS versus old fashioned Paddle Log

Lord Geoff,

Technically, GPS is a PNT (positioning, navigation and timing) system. GPS is sort of a trademark like GLONAS and others. The US GPS system provides many features beyond positioning...
Forum: General Sailing Forum 13-03-2015, 09:55
Replies: 442
Views: 38,404
Posted By transmitterdan
Re: speed through GPS versus old fashioned Paddle Log

Since nobody seems to be able to Google any more I took 3 minutes away from my lunch break today and searched a little. I found this paper:

https://nujournal.net/HighAccuracySpeed.pdf

A quote...
Forum: General Sailing Forum 13-03-2015, 09:40
Replies: 442
Views: 38,404
Posted By transmitterdan
Re: speed through GPS versus old fashioned Paddle Log

The mathematics are complicated and I don't pretend to know the formulas. But the GPS constellation at any point in time is "fixed" relative to the earth and the GPS receiver knows about that based...
Forum: General Sailing Forum 13-03-2015, 05:08
Replies: 442
Views: 38,404
Posted By transmitterdan
Re: speed through GPS versus old fashioned Paddle Log

I hear it's all done with magnets...but that can't be right ;)
Forum: General Sailing Forum 12-03-2015, 19:16
Replies: 442
Views: 38,404
Posted By transmitterdan
Re: speed through GPS versus old fashioned Paddle Log

For what?
Forum: General Sailing Forum 12-03-2015, 19:14
Replies: 442
Views: 38,404
Posted By transmitterdan
Re: speed through GPS versus old fashioned Paddle Log

No, it is not correct. GPS speed is not based on position in most GPS receivers. A boat traveling at 4 knots is only moving 2 meters per second. There is no way to accurately calculate speed from...
Forum: General Sailing Forum 12-03-2015, 17:00
Replies: 442
Views: 38,404
Posted By transmitterdan
Re: speed through GPS versus old fashioned Paddle Log

So far as I know all GPS chipsets do this. It does not have to calculate change in position. It only has to know the frequency shift to determine speed. Position is no where in the formula for...
Forum: General Sailing Forum 12-03-2015, 15:38
Replies: 442
Views: 38,404
Posted By transmitterdan
Re: speed through GPS versus old fashioned Paddle Log

You were taught incorrectly as were apparently many others so don't feel bad about it. From day 1 the GPS system was designed so that speed was as easy or easier to obtain than position. For many...
Forum: General Sailing Forum 12-03-2015, 12:20
Replies: 442
Views: 38,404
Posted By transmitterdan
Re: speed through GPS versus old fashioned Paddle Log

I have actually done this (anchored in a current). The paddlewheel struggled to measure anything and the GPS displayed 0-1.5 knots as the boat swung back and forth on the rode.
Forum: General Sailing Forum 12-03-2015, 12:12
Replies: 442
Views: 38,404
Posted By transmitterdan
Re: speed through GPS versus old fashioned Paddle Log

This is the first hit I got on Google:

Question: How does a GPS tracking unit calculate speed?

Best Answer: For average speed over a long distance it takes the distance traveled and divides it...
Forum: General Sailing Forum 12-03-2015, 10:28
Replies: 442
Views: 38,404
Posted By transmitterdan
Re: speed through GPS versus old fashioned Paddle Log

Believe whatever you like. Google:

How does GPS measure speed?
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