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post #11 of 19 Old 07-30-2018 Thread Starter
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Re: Garmin ChartPlotter Confusion

Apparently there is something amiss with the sentence that my B&G depth sensor transmits (DPT). Even though all my other NMEA 0183 sentences are read fine and the previous Garmin unit read it ok, the new Garmin 741 does not. I solved the problem by using some custom electronics to parse the DPT sentence and create a DBT sentence that the Garmin does accept. So all is well on my boat. Except that the GPSMAP 741 does not have all the sail assist features, mostly what is missing has to do with race starts and I have other ways to handle that. The Garmin 741 does have rose gauges and other displays that are useful.

While I was initially disappointed in the 741 I have come around to accept that what it is a big step up from what I previously had. And I got it a decent price.

thanks,
Ron
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post #12 of 19 Old 07-30-2018
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Re: Garmin ChartPlotter Confusion

Having a whole networked electronics suite of 2 gpsmap chart plotters, radar, depth and XM weather, and the certainty that soon the 10" mf display at the helm will die, my suggestion is to buy the very newest unit you can. When my gpsmap chart plotter at the helm dies, I will need a whole new electronics suite, not just a new chart plotter, to the tune of around 15k, as most of my present gear is no longer supported by Garmin. I've certainly had a good run on this gear, but instead of an affordable $3500 for a replacement plotter, 15k is a whole different kettle of fishies.
Why put yourself through that a few years earlier than you have to, just to save a few bucks now?

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post #13 of 19 Old 07-30-2018 Thread Starter
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Re: Garmin ChartPlotter Confusion

Not quite sure I understand what you are saying. The Garmin 741 is not the newest model, a generation old; but supposedly well tested. The chartplotter is the least of my concerns as my B&G instruments are approaching 30 years old. So I expect to have to replace them and their network at some point. The new network will likely be NMEA2000 and the 741 supports that so I envision an alternating replacement cycle of replace some electronics, replace some senors, repeat. As long as things are working I am ok with not replacing them to have the latest and greatest whatever. My boat is only a 35' sailboat; the current 741 plotter was had for less than $500. I can replace the B&G wind/depth instruments for $1500 (instrument price only). I don't know what it might cost to re-wire for NMEA2000 perhaps I can use the existing wiring in place (not sure), but pulling thru new wiring means mostly up the mast. I don't think I am looking at a $15K refit in the worst scenario. I will get there in time (or not) and since I am in my 70's maybe it is somebody else's problem!
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Re: Garmin ChartPlotter Confusion

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Originally Posted by CapnRon47 View Post
Not quite sure I understand what you are saying. The Garmin 741 is not the newest model, a generation old; but supposedly well tested. The chartplotter is the least of my concerns as my B&G instruments are approaching 30 years old. So I expect to have to replace them and their network at some point. The new network will likely be NMEA2000 and the 741 supports that so I envision an alternating replacement cycle of replace some electronics, replace some senors, repeat. As long as things are working I am ok with not replacing them to have the latest and greatest whatever. My boat is only a 35' sailboat; the current 741 plotter was had for less than $500. I can replace the B&G wind/depth instruments for $1500 (instrument price only). I don't know what it might cost to re-wire for NMEA2000 perhaps I can use the existing wiring in place (not sure), but pulling thru new wiring means mostly up the mast. I don't think I am looking at a $15K refit in the worst scenario. I will get there in time (or not) and since I am in my 70's maybe it is somebody else's problem!
The costs are for my gear not yours (where would you even put a ten-inch display?). What I am saying is if you cheap out and buy old tech now, you will have to keep buying old tech until you can no longer do so and then the bill will be much bigger.
I realize you aren't a charter boat, don't sail the West Indies nor do you probably rely on your electronics package almost daily as we do, so perhaps you really don't need to think ahead. Just mentioned it in case you wanted to.

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post #15 of 19 Old 07-31-2018
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Re: Garmin ChartPlotter Confusion

Quote:
Originally Posted by CapnRon47 View Post
Apparently there is something amiss with the sentence that my B&G depth sensor transmits (DPT). Even though all my other NMEA 0183 sentences are read fine and the previous Garmin unit read it ok, the new Garmin 741 does not. I solved the problem by using some custom electronics to parse the DPT sentence and create a DBT sentence that the Garmin does accept. So all is well on my boat. Except that the GPSMAP 741 does not have all the sail assist features, mostly what is missing has to do with race starts and I have other ways to handle that. The Garmin 741 does have rose gauges and other displays that are useful.

While I was initially disappointed in the 741 I have come around to accept that what it is a big step up from what I previously had. And I got it a decent price.

thanks,
Ron
Ron, could you please post a few sample sentences of what the depth transducer is sending? I have some contacts at Garmin and can ask them to look at it and issue a bug fix if needed.
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post #16 of 19 Old 08-01-2018 Thread Starter
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Re: Garmin ChartPlotter Confusion

Capta,
Ok, I understand where you are coming from, clearly that is the smart thing to do in your case. For me, one generation old means it has been tested and the bugs worked out of it. The newest Garmin is the 742, it is nearly twice the price of the older 741. The 741 has the same connectivity (which is what I was concerned with for future upgrades in network, Radar and Sonar), but fewer bells and whistles like the some of the sail assist (race start timer, etc) software.

jarcher,
This comes from my Garmin 741 Diagnostic log for NMEA communications:
57279,V,SRL,IIDPT,1.25,,
57305,V,SRL,IIDBT,4.10,f,1.25,M,0.68,F,

The DPT sentence is straight from my B&G instruments, it has always sent this format (depth in meters). The previous Garmin unit (545) was able to read this and displayed the depth correctly. The 741 reads it and shows it in the log, but does not display any depth value (--.-). Garmin claims this is an 'old' revision of NMEA and no longer valid (they are probably correct). My solution was to read the DPT sentence with some electronics (specifically KBOX https://hackaday.io/project/11055-kbox ) and convert that to the DBT sentence you see above. The Garmin 741 likes that sentence and displays the depth now. The Kbox is a home grown NMEA multiplexer, it reads in a couple of channels of NMEA 0183 (different speeds 4800, 38400), it can operate on that data and then send it out in numerous formats NMEA 0183, NMEA 2000, Log to an SD card, out over USB cable or out over Wifi. It also generates a new open source format called SignalK - Signal K » Welcome I run a signalK server using a RaspberryPi computer on the boat and all my instrument data is sent out over wifi in that format. It can be read by a free sharware chartplotter program called OpenCPN or by several apps on tablets or phones that display the data in numerical or gauge formats. With the exception of the depth sensor data all the 'hobby' electronics and such are independent of my boat instruments, displays and the Garmin chartplotter. They read the data and send it out, but for the most part my boat navigation does not depend on them. I do have a separate B&G depth hsitory display, but that display is slowly dying.

So I have my solution for now, but it Garmin thinks they can fix the DPT issue I would be happy with that too.

thanks,
Ron
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post #17 of 19 Old 08-01-2018
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Re: Garmin ChartPlotter Confusion

I too am leery of master mariner advice. Often doesn't apply to us.
I bought a recently discontinued Garmin Chartplotter that has every bell and whistle they made 8 months ago - how bad can that be? I think not too bad. And yes you could also buy the latest and it too will be out of date in 6 months, what's the point?
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post #18 of 19 Old 08-25-2018
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Re: Garmin ChartPlotter Confusion

Quote:
Originally Posted by CapnRon47 View Post
jarcher,
This comes from my Garmin 741 Diagnostic log for NMEA communications:
57279,V,SRL,IIDPT,1.25,,
57305,V,SRL,IIDBT,4.10,f,1.25,M,0.68,F,
Thanks Ron I'll pass this along.
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post #19 of 19 Old 12-09-2018
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Re: Garmin ChartPlotter Confusion

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Originally Posted by CapnRon47 View Post
I purchased the 741 and I have some issues. It does not show depth from my NMEA depth sensor. Garmin claims it is because my instruments are old, I am not convinced as my old Garmin read depth fine. Other than that I am happy with my decision also. The price was right and it has all the connectivity I could possibly need (much like the 742) the display is great and it is a good upgrade from my 8 year old 5" model.

thanks,
Ron
Garmin makes a Transducer Module ( fairly inexpensive ) that allows you to use any Legacy
Depth Transducer.

You cut off the old transducer plug and wire it directly into module.

Then the module plugs into Garmin Depth Port on 741 or 742, 942 etc
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