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Old 01-17-2016, 06:36 PM   #1
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GPS time lag...

We have a Garmin chart plotter and an I Pad on board with a GPS app. Which unit updates faster? We use GPS on some of our predicted log contests and lag time is a factor.
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Old 01-17-2016, 08:45 PM   #2
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Depends on the age of your Garmin GPS antenna. The newer one, GPS 19X samples 10 times more often than there previous model. Converted to the new antenna ($150 on ebay new in the box) during my refit and see a substantial difference in smoothness on the chart plotter.

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Old 01-17-2016, 09:20 PM   #3
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Old 01-17-2016, 09:30 PM   #4
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I don't know what the update rate is on an iPad, but a marine chart plotter/GPS will be once per second minimum, and anything less than 5 years old will be capable of 10 times per second.
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Old 01-18-2016, 01:00 PM   #5
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My Garmin 172C is ancient so I'm thinkin' the Sicilian's I Pad should be faster. We're gonna give a try for our next contest if we can find the right app.
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Old 01-18-2016, 01:10 PM   #6
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Our redraw lag time on several pieces of current generation chart ware is a minimum of 100 feet or so at 4 to 6 knots when factoring in skipper response time. With a 2 or so knot push current it is downright dangerous to use the plotter in narrow tight passages so visuals are an absolute must under these conditions. But, I am not a 20 year old gamer ------
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Old 01-18-2016, 01:26 PM   #7
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I installed a combination GPS antenna heading sensor last Spring. Both update at 10 hz (10 times per second). The only lag time I see on my plotter is when it redraws the chart. That can take a couple of seconds. The only other lag I see is when I turn the radar overlay on. That can take up to 20-30 seconds to stabilize.
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Old 01-18-2016, 01:27 PM   #8
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We set the filter time at 5-10 seconds on our GPS to smooth our speed and course out. Have you looked at that on your plotter?

Here's an in depth article on update rates vs distance for GPS. Probably too much information.

http://waset.org/publications/7783/t...n-applications
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Old 01-18-2016, 03:33 PM   #9
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So 0.1Hz gives me a refresh rate of once every second. At an average boat speed of 8.5 knots that should be adequate for a predicted log contest. Don't know if I can decrease the lag time with my old Garmin 172C. I'll find out this weekend.
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Old 01-18-2016, 04:31 PM   #10
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Let us know, if there is a difference between the 2. I would think the iPad would be the better tool give technology and the age of the Garmin vs the iPad. And good luck on the contest.
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Old 01-18-2016, 09:22 PM   #11
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Quote:
Originally Posted by ancora View Post
So 0.1Hz gives me a refresh rate of once every second. At an average boat speed of 8.5 knots that should be adequate for a predicted log contest. Don't know if I can decrease the lag time with my old Garmin 172C. I'll find out this weekend.
0.1 Hz gives you a refresh time of 10 seconds, not 1 second. However, the refresh rate of modern GPS units is closer to 10 Hz or 0.1 second. If you are interested in timing to fractions of a second in log racing I want you to teach me how to do it. At 8 kt. a boat travels about 1 ft. in 0.1 sec. Thats pretty good navigation!

Paul
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Old 01-18-2016, 09:26 PM   #12
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Don't sense any time lag on GPS here.
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Old 01-22-2016, 01:24 PM   #13
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Downloaded Spyglass app on our iPad. We will try it out tomorrow and compare the readings with the chartplotter.
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Old 01-23-2016, 03:59 PM   #14
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Took the boat out this morning and both iPad apps failed to show lat/lons. Got our the Sicilian's phone app and it worked out fine. Could not detect any time lapse between the phone app and the Garmin chart plotter. Now if I could only get the chart plotter to read the speed in knots to a second decimal point.
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Old 01-23-2016, 04:40 PM   #15
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There has to be a speed app for an iPad out there so you can read knots to a second decimal point. But would it really make a difference or slow you down over distance as you're trying to correct for the optimal speed?
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Old 01-23-2016, 07:42 PM   #16
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I do not make RPM changes during the contest as I cannot read the currents as well as I should. We make a speed run while transiting to the start line, ascertaining the proper RPMs considering the current predictions at the time, and the current factor between two or more buoys.
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