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Old 09-09-2009, 06:13 PM   #1
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Default Chartplotter/GPS/Autorouting

I have a hand held Garmin Colorado 400c that I have been pleased with over the last year. The 400c comes preloaded with BlueChart® g2 (with limited capability) marine maps. I also purchased the North American Navigator maps so I can use the unit in my truck. This unit is packed full of features...tides, compass, barometer etc and I find that the charts are highly accurate, displaying known rocks in my area of boating, channel markers etc. But what it can't do is 'auto-route' me a course...meaning...I set a waypoint as "My favorite dockside restaurant" which is 20 miles south and have the unit guide me out of my very curvy channel, down to the 'restaurant' channel (around any obstacles along the way) into a slip at my destination. What I get now is 'as the crow fly's' navigation i.e. I set a waypoint and I get a line straight to my destination. So it's a matter of setting numerous waypoints like flying from one VOR tower to the next. Do marine 'chartplotters' autoroute? Garmin doesn't explain the differences on their site. Doing some searching online I see the question asked often but the answers aren't applicable with todays' GPS units. The answer being that 'GPS units tell you where you are and chartplotters allow you to set waypoints for where you are going'. So maybe there isn't a difference now?

I read in one of my boating magazines how a couple ran ashore one night because they had their trawler set on 'autopilot' and went to bed! Can autopilots steer a boat based on charts or is it simply a 'brink on the gas pedal' sort of thing?

It would be nice if I could set a series of waypoints and have the unit guide me concurrenlty i.e. reach the waypoint and the unit switches to the next waypoint etc to the destination. Maybe this is what chartplotters do?
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Old 09-09-2009, 09:10 PM   #2
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Default Re: Chartplotter/GPS/Autorouting

My understanding of the Garmin auto routing feature (which my 541s has) is that you tell it where you want to go and it will plot a course to that destination, keeping clear of known obsticles.

I've yet to test it though.

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Old 09-10-2009, 12:22 AM   #3
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Default Re: Chartplotter/GPS/Autorouting

Thanks Dan - I now see on Garmins page for your unit that ... "Auto Guidance technology searches through all relevant charts to create a route you can actually follow — one that avoids obstacles, shallow water, buoys and other obstructions".
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Old 09-10-2009, 10:04 AM   #4
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Default Re: Chartplotter/GPS/Autorouting

I have the garmin 4008 and I use autorouting it works great but I check it on my paper chart to be sure .
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Old 09-10-2009, 01:15 PM   #5
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Default Re: Chartplotter/GPS/Autorouting

Having flown airplanes with GPS for 15 years, I can re-iterate the advice to ALWAYS keep a chart on your lap, even when using GPS.

GPS's are great for "where-am-I-right-now, and semi-great for planning, but they are "dumb" boxes and can't look at the entire picture like a competent navigator. I'm glad some of the boxes are going away from the "straight-line route" and routing more intelligently, but the Captain is ultimately responsible for every mistake made by the GPS or its programmer.

And guiding your autopilot via GPS is great, but you've gotta stay at the helm to monitor it! (I can't believe people walk away, believing the autopilot will handle everything!) GPS can't see the debris floating in your path or the other autopilot-guided boat coming right at you!

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Old 09-10-2009, 01:51 PM   #6
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Default Re: Chartplotter/GPS/Autorouting

I make the wife follow the paper chart while I follow the GPS when we're cruising. The paper chart is useless if you don't know where you are after the electronics have died. This also forces her to keep sharp and practice navigation. Who's going to get you, your loved ones, and your boat back to the dock if you're incapacitated? Plus it makes it easier than having to zoom in and out on the GPS all the time. I use to chart to see and anticipate what I expect to see coming up on the chartplotter.
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Old 09-10-2009, 04:42 PM   #7
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Default Re: Chartplotter/GPS/Autorouting

We also keep charts on the boat - just in case. Problem is that it's often difficult to read the charts when running at speed in choppy waters in a small boat. Yes, you can slow, read, back to cruise, etc-etc, but it's far easier to be able to glance at the screen - and probably safer if out alone.

One nice feature of the unit I have (and probably most units) is it keeps "track" of where I've been. If I run from point A to point B it paints the track on the screen and saves it. Basically like laying down it's own way points at specific intervals. When it's time to return from B to A I can simply follow that same track back in.

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Old 09-29-2009, 04:49 AM   #8
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Default Re: Chartplotter/GPS/Autorouting

GPS can also go OUT! I had this happen to me on a run in North Florida. It was announced on Channel 16 all day long, but if you don't monitor your VHF, you would never know. The U.S. Government will very rarely test out their failsafe systems, where they actually change the signal so that the accuracy is severely disrupted. I am assuming this is to prevent GPS guided weapons from our enemies striking their targets. I only experienced this once in my 10 years running yachts, but that day my plotter had me 5 miles inland. Something to be aware of when using auto routing. I would NEVER trust that technology, although I would use it if I had that unit.

I did have the opportunity to have a system that would change course at waypoints through my autopilot. I played with it, but never trusted that either. When you are cruising through the Bahamas, there are some places that if you miss your waypoint by even 100 yards or less, you are on the coral. My opinion is to play with that technology, but never rely on it. It is a cool bell and whistle, but not good enough to trust your life and others lives with.

Some of the best things you can do to check your GPS while underway is to verify depth on your plotter to your sounder. Also, check a buoy every once in awhile and make sure it is the same number on your GPS buoy icon you are flying by at 30 knots. Stay safe!
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Old 10-05-2009, 02:50 PM   #9
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Default Re: Chartplotter/GPS/Autorouting

Quote:
Originally Posted by captmarc
GPS can also go OUT! I had this happen to me on a run in North Florida. It was announced on Channel 16 all day long, but if you don't monitor your VHF, you would never know. The U.S. Government will very rarely test out their failsafe systems, where they actually change the signal so that the accuracy is severely disrupted. I am assuming this is to prevent GPS guided weapons from our enemies striking their targets. I only experienced this once in my 10 years running yachts, but that day my plotter had me 5 miles inland. Something to be aware of when using auto routing. I would NEVER trust that technology, although I would use it if I had that unit.

I did have the opportunity to have a system that would change course at waypoints through my autopilot. I played with it, but never trusted that either. When you are cruising through the Bahamas, there are some places that if you miss your waypoint by even 100 yards or less, you are on the coral. My opinion is to play with that technology, but never rely on it. It is a cool bell and whistle, but not good enough to trust your life and others lives with.

Some of the best things you can do to check your GPS while underway is to verify depth on your plotter to your sounder. Also, check a buoy every once in awhile and make sure it is the same number on your GPS buoy icon you are flying by at 30 knots. Stay safe!
Excellent advice! Thanks!
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Old 10-05-2009, 05:19 PM   #10
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Default Re: Chartplotter/GPS/Autorouting

We have a Garmin 545S with the Bluecharts G2 for our area and it does a pretty fair job of auto routing. When I set up the GPS initially it asked for our boat's draft and how much overhead clearance we needed, which I gather it uses in calculating course changes. I believe it factors in tidal levels also. For the most part it's point and shoot - Turn on the GPS, let it figure out where it is for a few moments, tell it where you want to go and it plots around islands, shallow areas, etc...

As said above, we still keep our paper charts close, as on some occasions our plotter will cut corners - say between a marker buoy and a small shoal - there might be enough water at mean tide if exactly on course, but I would rather round the buoy instead to be safe. Less than a hundred yards in the wrong direction could be the beginning of a really bad day. Dear ol' Dad was a navigator in the Navy and taught me how to plot courses at a very young age. Some habits die hard. We also run a sounder and double check everything.

If anything, I've found it to be pretty conservative with regard to depths, sometimes routing us around small islands when I have been through passes it is trying to avoid, many many times. If mine disappeared tomorrow I would buy another (but likely one with a slightly bigger screen. My eyes aren't getting any younger). Not exactly the cheapest kit on a boat, but well worth the money.
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