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Old 03-07-2015, 21:07   #16
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Re: Simrad speed and cog differences

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Originally Posted by colemj View Post
Yes, and also doing timed distances on slack current water, or just comparing SOG and STW in a no-current, no-wind, no-wave area.

If it is an argumentative point, I will admit that we are probably only calibrated within 0.1kts.

I thought a GPS, compass and paddlewheel log constituted an "electronic current measures thingy".

Of course, I don't plot AIS targets using sextant and paper, so what do I know...

Mark
What I am saying is the paddle wheel reading today is unlikely to be the same next week or the week before due to growth on/around shaft, on sensors ( fixed and on paddle). Any time you get a reading from your paddle wheel you have no way of knowing its current accuracy.
The integration of REAL TIME AIS data with paper chart navigation was a wind up of our paper chart/ sextant navigators..........bit like using a horse and dray to move your BMW V8 turbo diesel around town.......
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Old 04-07-2015, 07:07   #17
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Re: Simrad speed and cog differences

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What I am saying is the paddle wheel reading today is unlikely to be the same next week or the week before due to growth on/around shaft, on sensors ( fixed and on paddle).
Are we the only ones who regularly pull and check/clean our paddle wheel? I do so before each passage, and if we are anchored anywhere for a length of time, I pull it out completely.

Our experience has been that the speed log is either working and accurate, or is not working at all and needs to be cleaned. I can't recall anytime that it was inaccurate by reading, say, a knot slower than expected. I think the paddlewheel is so sensitive, that any growth at all simply stops it. Otherwise, it works.

This was also my experience with all our previous ones.

Sorry - didn't catch the windup. I was attempting a windup. Guess we are all wound up now?

Mark
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Old 04-07-2015, 07:20   #18
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Re: Simrad speed and cog differences

I am in Mark's camp. I like things to work whether or not it's 100% accurate. Paddle speed vs Sog is a useful indicator of tide change in places like the ICW. But back to my question; i assume my sog on the mfd is ais from the mfd's internal ais antenna. What is the source of sog on the simrad combi instrument that's about 1mph different from sog on the mfd? It isn't related to the paddle wheel speed is it? How could it be? Shouldn't it be the same as the mfd?
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Old 04-07-2015, 07:38   #19
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Re: Simrad speed and cog differences

Sorry to get off topic! Yes, SOG should be the same for all GPS sources and STW doesn't come into play. I don't have an explanation for your case, other than to check that the damping isn't over-agressively set on one.

Mark
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