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  #1  
Old 02-27-2007
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GPS proliferation!

I'm gearing up after a few years off the water and am struck by the ubiquity of GPS these days. Radar takes GPS input, navigation software takes GPS input, even the VHF takes GPS input. And I assume the GPS receiver takes GPS input. Generally, does all this input come off a central GPS unit somewhere? Can one buy cables with endless connectors for all these devices? Can an antenna splitter be used for a GPS antenna to send a signal to more than one GPS receiver? Can anyone point to a good source of information about the overall theory/plan of a modern nav station? The more I think about it, the more my head hurts. Thanks.
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Old 02-27-2007
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wungout,

And no wonder! It's all very confusing these days.

There are at least two schools of thought here:

(1) connect everything (mainly, just because you can IMHO); and

(2) think carefully about which devices you really want to connect.

Most GPS receivers these days have an output capability via the ubiquitous NMEA 0183 protocol. This puts a coded "sentence" on a two-wire output which can then be connected to other devices.

Being both a long-term navigation nut and an electronics junky, I thought long and hard about what I really wanted to connect together. I connected my GPS unit to my onboard PC-based charting setup (Ocean Navigator) only after several long trips during which I watched the reported GPS positions carefully and plotted them manually on the PC. I found that this was a pretty good thing, and connected the two.

When I installed a DSC VHF radio, I connected the GPS to it. This allows me to read the current GPS lat/long on the radio and on the remote microphone in the cockpit (this is really redundant, since I have other readouts of GPS position at the nav station and at the helm) and, more importantly, allows the DSC to function as designed and automatically transmit the boat's position in an emergency.

I have NOT connected the GPS to my onboard Furuno radar, and have no plans to do so. Not needed.

And, I have not and will not connect my GPS to my autopilot. Yes, it's capable of accepting GPS input, but I think it's a mindless and very dangerous thing to do....a great way to increase the numbers of "GPS-assisted groundings".

These are just my preferences. Others will have theirs.

Bill
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Old 02-27-2007
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Wungout,

The theory of the modern nav station is make it bigger and bigger for all the neccesary and essential equipment you must have or you will be lost and sunk and run aground and stranded on a island (all at the same time).

The plan is for electronics manufacturers to make lots and lots of money.

Now, does that clear it up, or were you interested in a real discussion?? (smile)

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Old 02-27-2007
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I think btrayfors has covered it pretty well, especially from a philosophical standpoint. Note that he experimented with the system before connecting the GPS to his navigation protocol. Obviously he was concerned with the dangers of looking at a chartplotter with GPS input and blindly expecting the information displayed to be true. I suspect that you would find, even with all of the high tech gadgetry, he still plots positions on a paper chart. That being the only way to monitor whether your nav "system" has gone goofy and you are not really in the parking lot of west marine. I agree fully with his questioning of why hook to your radar-certainly a "just because you can" idea with no real merit to it and great potential for confusion.

I would add that the more things you tie in, the more wiring you are going to have, and the more potential for a difficult to find stray ground messing up the whole system. KISS should be the watchword. As mentioned often on these pages, the reliance on a chartplotter in no way relieves the prudent navigator from plotting fixes on paper charts. With the advent and proliferation of automobile mounted GPS units it is only a matter of time before we hear of somebody turning in to the side of a building or some-such because their GPS told them to do so.

The safest way to view your GPS is as a really fast sextant. Do everything as if you were taking a celestial sight. Everything else is just a convenience. To carry the automobile analogy a little further, would you drive down the road in fog with your GPS for your only guidance? As Dad pointed out, the marketing people have alot more sway than the navigation people do in the production of these things. Somewhere, buried away in the fine print, is the notification that the stuff is not warranteed to do anything.
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Old 02-27-2007
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And, I have not and will not connect my GPS to my autopilot. Yes, it's capable of accepting GPS input, but I think it's a mindless and very dangerous thing to do....a great way to increase the numbers of "GPS-assisted groundings".

Me too! After entering hundreds of waypoints AND making mistakes that I fortunately caught when my waypoint heading and distance on the chartplotter did not agree with my paper plots...I didn't want to let the auto pilot follow those waypoints blindly. It is way too easy to make an error.
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Old 02-27-2007
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I'm with Btray and Cam on connecting GPS and autopilots, but kind of like the ability to display a GPS waypoint on your radar screen.... it's one more piece of info (granted, available elsewhere too) to complete the picture.
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Old 02-27-2007
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Some answers and some comments

Hello,

Here are some answers and some of my opinions.

Most boats with GPS will have one main chartplotter. The GPS is internal to the plotter. It may have an external antenna, but the GPS unit is in the plotter. Other devices that need position information (DSC VHF, repeaters, autopilot, etc.) get the data from the chart plotter. The 'standard' way devices communicate today (as previously mentioned) is NMEA 0183. This is a two wire system. Most devices will have a NMEA in and NMEA out connections, so the data can travel round and round. This is bad because the wires have to go all through the boat. There is a new standard, NMEA 2000 which is much faster and easier to use. With NMEA 2000 you just connect the wire with a standard plug and it does the rest. Unfortunately, there aren't many NMEA 2000 devices out there yet.

IMHO, for safely reasons you should have at least a DSC VHF. Then when you press the 'distress' button the coast guard will know where your boat is. There is lots of info on DSC if you are interested.

I recently bought a newer boat and will be upgrading the electronics on it. I am adding a 5" color chartplotter and DSC VHF. I will connect the autopilot to the chartplotter, but I don't know how often, if ever, I will use that feature. On my old boat I had a smaller chartplotter. It was great when I was trying to get somewhere to have accurate ETA, distance to next waypoint, tide and current information, off track information, etc. I still make manual log entries every hour, and I record my position on chart.

I don't think of the GPS as a modern version of the sextant. It can do so much more. When I sail I am, for all practical purposes, singlehanding. My family may be with me, if so, my wife will be watching the kids and helping, but sailing and operating the boat is really my responsibility. So anything that will reduce my work load and provide highly accurate information is a great benefit. A sextant can't give you tide and current information, instant ETA, distance to next waypoint, identify the navaid 2 miles away, etc.

Considering how cheap they are, there is no excuse not have a primary and a back up. I have an older Garmin Etrex Legend for that.

Good luck,
Barry
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Old 02-27-2007
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I'll sound off for no gps to autopilot connection. Asking for trouble really. And is it that hard to turn manually to a new heading?
I will say though, that I have used Nobeltec Nav software on a delivery that took radar input and did plotted Arpa targets. Nice to see a visual representation of the commercial traffic on screen. Still important to use your eyes and conciously miss things but the caculations were done by the software so added redundancy to the radar's arpa. Haven't tried it the other way.
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In my navigation wish book: fathometer first, radar second, GPS third.
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Old 02-27-2007
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One thing I'd mention about NMEA 0183 and GPS units. The output on a GPS can generally handle up to four devices...any more than that and you'll probably want to get a multiplexer.
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