Whats the differece between marine and auto gps units?

[Vara]

On my car Navman navigator, the only way I can find to get lat/long out of it is to use the photo facility, which displays lat/ long at the bottom of the taken pic.

Limited utility for boat navigation, but it does work accurately mid channel.

 

[DaveS]

As others have said, marine GPS units without plotters are becoming rare, though eBay might yield an old Magellan 300 series unit for not much. A car satnav is not the only alternative, though. Simple hand held GPS units for hillwalking / geocaching etc. are still readily available new, though again higher spec. units incorporating mapping are gaining ground. Something like the base model Garmin Etrex should be available from Amazon for about £60 and adding a 12V cable and a mounting bracket should still give an overall cost of under £100. AFAIK lat / long is supported by all of them, and most will handle waypoints.

 

[Pavel]

While I'm at it has anyone any experience of USB GPS dongles which come as cheap as $17 on ebay and claim to be compatible with navigation software ef open cpn??

Yes. Well, a bluetooth one, but it doesn't matter. I've got a Globalsat dongle, and it works with openCPN, OziExplorer, Google Earth, EarthBridge and any other software I've tried. All you need is it to be NMEA-compatible, and most of them are. I'm planning to buy a wired GPS mouse to hook it up to the DSC.

Good point about the difference between nautical and land miles, I hadn't thought of that one!

Not if you've got a dongle, in which case you could choose units you like in the software. My old eTrex had this option too.
And getting back to your original question...

Whats the differece between marine and auto gps units?

IMHO just another case of acute marine-price-itis.

 

[elton]

As others have said, marine GPS units without plotters are becoming rare,

That is so completely and utterly wrong. What are Garmin doing selling "rare" handhelds GPS-only devices?

 

[Pete R]

All I really want to do is display a lat and long..... so would an automotive unit do this, even when crossing oceans?

My answer to your question is yes. And thanks for asking as I have just searched on line and found map updates I didn't know about.
View attachment 16817
I have a 6 year old Garmin Quest car sat nav. They are now discontinued but just found one on ebay.
This displays Lat/Long which is more accurate than my car tracking device and the same accuracy as my laptop and usb GPS
I can change the setting to Nautical Miles with either feet or metres.
It has a compass screen.
It will give distance/direction to a waypoint and do routes at sea. "Road unlock"
It will accept magnetic variation input.
It will leave a track and there is a track back function.
There is a save location button which could be used as MOB.
It has sunrise/sunset times.
It is also waterproof.


The screen is small but all the controls are off screen which I like.
The longest journey I have used it on at sea is on a ferry from Venice to Patras in Greece.

I would be more than happy to use it at sea with charts.

 

[barnaclephill]

As others have said, marine GPS units without plotters are becoming rare, ... Simple hand held GPS units for hillwalking / geocaching etc. are still readily available new.. Something like the base model Garmin Etrex should be available from Amazon for about £60 and adding a 12V cable and a mounting bracket should still give an overall cost of under £100. .

Another vote for a simple handheld unit, with power cable option, used for boats or hiking.
Sunlight viewable might or might not be an issue, backlight at night might be.
Compared to a car model, the handheld hiking/boating model can be programmed in KM, NM and land miles, and the distance to a waypoint might be important. It was for me once, when the waypoint was in the middle of a 200 metre wide bay after the sun had set - getting that accuracy, in addition to the spotlight, made me chuffed at how good it is, and how much that sort of accuracy and waypointing ability is needed.

The HH will do the calculations, as well as giving the lat/long for you to mark or write down, it will in the next 3 seconds tell you how far to your waypoint, the average speed you've done, your avergaging speed now, etc. It will give moon rise and set, sun rise and set. It gives a compass rose, to check your main compass to (deviation), etc. The etrex also can be made to draw a simple map of your waypoints and your track. Useful to delineate a waterway when you return there at night. Also good is the instant "mark waypoint" function for when you drop something (anchor rode) and come back a month later within 3 metres and successfully retrieve it from 5 metres of murky water.

In summary, for the cost, better than a car's unit.

 

[Pete R]

In summary, for the cost, better than a car's unit.

Just for the sake of an argumentapart from the moon rise/set times how is your handheld any better than my Garmin car sat nav above which also has a map and can get me home in the car?

 

[nimbusgb]

The GPS native reference geoid is WGS 84. If your automotive unit is 'several minutes out' there's something severely wrong somewhere.

Marine systems to be interfaced with other things need NMEA output OR a means of getting there -perhaps USB to PC and then RS232 output and either 'bash it' or convert the levels. If you don't want to interface then anything will do.

Do you *need* Nautical Miles? I doubt it really. You can always work in Km or leagues if you fancy. ( internally it's all metres anyway )

Market for 'Car navigation systems' = millions wheras market for marine nav systems = thousands thus the difference. Inside the unit at the core of receiving the signal and producing a lat and long they are all basically the same in fact there are probably less than 10 real core receiver engine manufacturers.

Accuracy these days of any GPS is sub 3 metres 95% of the time, car,plane or boat unit.

 

[Dave_Seager]

Just for the sake of an argumentapart from the moon rise/set times how is your handheld any better than my Garmin car sat nav above which also has a map and can get me home in the car?

A typical car unit is unlikely to be able to give you course and distance to a waypoint. My TomTom will not even allow me to define a waypoint at sea.

 

[electrosys]

Accuracy these days of any GPS is sub 3 metres 95% of the time, car,plane or boat unit.

Are you sure ? - the PPS (Precise Positioning Service) of the US Navstar-GPS is claimed by them as having a 17.8 m horizontal accuracy and a 27.7 m vertical accuracy.

But there are also additional uncertain errors to take into account:
Electrical noise in the receiver, a well as phase noise in the PRN code modulation can degrade accuracy by about 2 metres.

Should satellite clock errors not be immediately corrected by the ground station, this will degrade accuracy by about 1 metre.

Errors in orbital position estimation, approx. 1 metre.

Unmodelled signal propagation delays in the troposphere, changes in humidity, temperature and pressure changing the refractive index, approx. 1 metre.

Multipath (the effect of satellite signals bouncing off obstacles and arriving from several directions each with different time delays) typically degrade accuracy by about 0.5 metre.

Unmodelled ionospheric signal delay, of which one-half can be compensated for, can result in an error as high as 10 metres.

Geometrical Dilution Of Precision (GDOP), where the angles to the satellites in view are very similar, will result in inaccuracy in solving the coordinate equation, which will further degrade the solution.

Because all of these sources of error will fluctuate in time, users may experience substantially better accuracy at some times, and worse accuracy at other times.

So - to believe in a reliable accuracy of 3 metres is living in a fool's paradise.

 

[RAI]

So - to believe in a reliable accuracy of 3 metres is living in a fool's paradise.

Most GPS receivers today use the output of the WAAS / EGNOS / MTSAT satellites which correct the major GPS errors. Those systems claim an improvement to below 2m horizontal. Some errors still remain, for example multipath.

 

[Bosun Higgs]

Yes went to the garmin site but to be honest it totally baffled me! We are a bit backwards on our boat and use a minimum of electronics, I want to see a lat and long and the compass heading on the one we have (152) is useful to make sure we are still heading in the right direction!

We carry 3 handhelds, the unit that is failing is the one on the navigation station. We like it as it has a large display that we can see from our sea berths when on a passage...To pay £300ish for that when an auto one is around £70 seems a bit daft

I will send Garmin an email and see what their response is

Garmin do a repair service costing about £50. For that they will either get your existing unit back to new or replace it with similar.

 

[mcframe]

Good point about the difference between nautical and land miles, I hadn't thought of that one!

I used to use a Garmin GPSMap65 (now one of four backups after SH plotter, before iPhone† & Foretrex and really old eMap) on land and sea with boat, car & motorbike mounts.

I had to remember to switch the settings around each time....

"Honest officer, I thought I was proceeding northwards up the A3 at 70 statute miles per hour...."

An ebay eTrex used to be the standard suggestion for minimal marine lat/long or grab bag - even the most basic current eTrex still offers statute, nautical or metric.

† With TomTom app for land and Navionics app for sea and a couple of other random GPS apps.

 

[mcframe]

To the best of my knowlege there's no such thing as an ""auto gps unit". If you mean a "satnav", it's an entirely different thing to a marine gps, such as the Garmin GPS 72/76. Differences are too numerous to mention. Perhaps someone who owns a "satnav" can tell us what the display shows when you're 200 miles away from the nearest road.

hehehe.

GPSR snobbery in action.

He has a "satnav" in his car.
You have a "moving map" in your aircraft.
I have a "chartplotter" on my boat.

I mentioned that to a friend a while back (he's into precision timing) and he trumped it with "But all of my GPS receivers are 19" rack-mount" ;-)