Chartplotter

[donm]

Going to buy a plotter - probably a Lowrance. I am going to site it in the cockpit and remove when not aboard so would prefer an internal aerial but as I already have a GPS can I "share" the existing GPS aerial with the chartplotter?

 

[nigelhudson]

Why? Yes you can supply an NMEA signal to the Lowrance plotter but then you are reliant on a single GPS receiver. This means that you have a single point of potential failure. We've just installed a Lowrance plotter and made it complteely separate from the existing GPS and have mounted the receivers in different parts of the boat. Thus we have the security of two completely separate systems.

 

[tangofour]

And which one do you believe when there's a discrepancy?

 

[Anonymous]

I do a similar thing with my Navman. I have an integrated Raymarine system that encompasses the radar/plotter autopilot, instruments and DSC but bought a Navman with integral GPS as the Raymarine has a monochrome screen. I have mounted two positions since I have a deck saloon and a steering position below and the Navman is wired into the NMEA bus via a plug and socket (one of the small chrome? circular Bulgin multipin) I move the Navman to the position I want it.

This means that I can run the Navman from the external Raymarine signal which it finds on the NMEA bus but also, and importantly for me, I can use the Navman to send the destination information to the Raymarine autopilot - this happens automatically just by them being on the same NMEA bus. It works very well and I have the security that if either GPS dies the other will take over and I have a more modern plotter without having had to upgrade the radar/plotter.

 

[Twister_Ken]

>It works very well and I have the security that if either GPS dies the other will take over<

Unless the power supply dies and kills them both?

 

[stevebirch2002]

Tidal Problem

Has the Tidal problem been sorted on the Lowrance Plotter?

 

[jwilson]

I had for a while two independent GPS's with aeriels 6 ft apart. The displays usually agreed to within .001 of a mile (which happens to be 6.08 ft).

Seriously though, navigation is about judgement rather than equipment - using the best data available to you from all sources, including most importantly your eyeballs. The further you go, the more you find places where the charts are wrong, so GPS super-accuracy is actively dangerous. Or even your ears. I remember (long ago before GPS and without even an echo sounder) realising I must be getting close to the cliffs of North Devon in fog when I started hearing cows mooing.....

 

[Anonymous]

[ QUOTE ]
Unless the power supply dies and kills them both?

[/ QUOTE ]Well sort of...I have a small 7Ah sealed lead acid battery that I keep charged up with a small solar panel which I use for odds and ends where I need 12V remote from a socket. I can easily rig this to power the Navman if needed but I wouldn't have an autopilot. I also have a handheld Magellan from circa 1997/8 which would give me a lat/long under any circumstances.

That's one reason I keep paper charts on board....I can always revert to traditional nav aided by GPS positions if the high tech stuff goes pear-shaped.

GPS heads are very vulnerable, as are the cables bringing them inside. Then you have the distribution to the various things that need the signal - autopilot, DSC, radar and if any of these things fail they could take down the whole GPS system. Frankly, the most important piece of information you have have is your position - given a choice of only one piece of information available to you, you would have position.

 

[Guest]

[ QUOTE ]
Going to buy a plotter - probably a Lowrance. I am going to site it in the cockpit and remove when not aboard so would prefer an internal aerial but as I already have a GPS can I "share" the existing GPS aerial with the chartplotter?

[/ QUOTE ]

Mmmm had to think on reading this ... as the idea to buy an internal antena gps Lowrance / or other is not a bad idea. I wish I had instead of the remote antena job I did.
Now onto another gps signal ... as most plotters come with gps either internal or external now - why the question ? If it's back-up if plotter gps fails - then no problem - as long as your existing gps outputs NMEA - then the lowrance of whatever will accept it. You just have to decide in the menu whether its lowrance or another gps signal is uses.

My Lowrance 3500C has a RS232 plug and lead (cut of a redundant serial mouse !) permanently connected to its nmea lead. I can either feed a PC with gps from the Lowrance ... or into a junction box and accept gps from my eTrex ... and still have plotter and pc if required.

 

[bluedragon]

[ QUOTE ]
Going to buy a plotter - probably a Lowrance. I am going to site it in the cockpit and remove when not aboard so would prefer an internal aerial but as I already have a GPS can I "share" the existing GPS aerial with the chartplotter?

[/ QUOTE ]

I had a problem when trying this with my Lowrance 3500C. It read the NMEA data from a Garmin 128 output, and showed the position, but speed and other functions would just not work. Try it first before going down this route.

 

[Richard10002]

[ QUOTE ]
Going to buy a plotter - probably a Lowrance. I am going to site it in the cockpit and remove when not aboard so would prefer an internal aerial but as I already have a GPS can I "share" the existing GPS aerial with the chartplotter?

[/ QUOTE ]

Not sure why you would want to share the existing aerial with an internal aerial unit. I think it is possible, but you would only want to do it in an emergency, (i.e. if the internal aerial failed.

I have mine at the wheel, but have also got a 2nd power cable so I can mount it at the chart table - where the internal aerial doesnt work. I guess you might want to use an external aerial in this situation, but I dont bother as I am usually using it for planning if it's at the chart table.

Cheers

Richard

 

[Guest]

[ QUOTE ]
[ QUOTE ]
Going to buy a plotter - probably a Lowrance. I am going to site it in the cockpit and remove when not aboard so would prefer an internal aerial but as I already have a GPS can I "share" the existing GPS aerial with the chartplotter?

[/ QUOTE ]

I had a problem when trying this with my Lowrance 3500C. It read the NMEA data from a Garmin 128 output, and showed the position, but speed and other functions would just not work. Try it first before going down this route.

[/ QUOTE ]

Interesting ... will have to check again ... as when I checked my eTrex connected to the plotter - I think it did compute speed etc. Let's be honest - speed and course etc. are only maths between successive positions ...

have to check that one ... good point !!

 

[bluedragon]

Yes it surprised me as well. I was going to use the Garmin NMEA output to avoid installing the Lowrance GPS receiver unit...but it just didn't work properly. I had a similar problem in connecting the GPS128 to a Silva S15 VHF...the latter kept dropping the position coordinates. Also tried an old Garmin hand-held in place of the fixed GPS..same issues. When connecting the S15 to the Lowrance NMEA output, no problem! So I'm concluding that possibly the Garmin NMEA output is in some way non-standard or mis-read by the Lowrance and Silva units in a way that corrupts the computations by the latter?? Has anybody else noticed this?