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ContinuousWave: Small Boat Electrical
Garmin GPSMap 741 Chart Plotter and SONAR
|Author||Topic: Garmin GPSMap 741 Chart Plotter and SONAR|
posted 02-02-2014 04:51 PM ET (US)
I'm redoing my all-in-one unit with either a Garmin or Lowrance product. I like the Garmin 741: user friendly, touch screen (not sure if I want that but it's what we do these days),and pulse-compression SONAR technology. Weigh in on this: touch screen, chirp or pulse-compression SONAR, and the 741 itself. Look fantastic at my run thru at West Marine & Seattle Boat Show. I'm a San Juan Island salmon fisher predominantly.
posted 02-02-2014 10:21 PM ET (US)
Last I checked, Garmin is ONE of the only brands (if not THE only brand) that includes tide charts. That's a big plus for me. My next combo unit will be a Garmin.
posted 02-03-2014 09:14 AM ET (US)
The introduction of pulse-compression SONAR techniques into less-expensive recreational SONAR devices has been very rapid, and the new technology has created something of an upheaval in the market.
As often happens in electronics, once the circuitry and software have been developed, the marginal costs of the new technology rapidly falls, and one finds that the next generation of electronics costs no more than the prior generation, while delivering more performance. On that basis it is hard to resist the new technology, and the older technology is usually soon forgotten and abandoned.
In the case of continuous wave frequency-modulated SONAR with pulse compression, there is one component in the systems whose cost cannot be so easily reduced: the transducer. To obtain the benefits of the new method and new electronics, the transducer must be significantly different from the older SONAR transducers. The transducer for a continuous wave frequency-modulated pulse compression SONAR must be low-Q and broad band. This results in a much more expensive transducer than needed for traditional SONAR units. Typically the transducer will be an extra of $400 or more, compared to usually no extra cost in the traditional units.
Whether or not the full benefits of the pulse compression technology will be realized in all application of the technology is hard to say. For shallow water fishing, the traditional SONAR techniques have been refined to a high degree and produce very good results. For use in much deeper water, there is no doubt that pulse compression techniques are superior. But if you are angling in 50-feet of water, perhaps you don't need the new methods.
There is also a consideration of the size of the transducer. The low-Q broadband transducers tend to by physically much larger than traditional transducers, and since on a small boat will be transom mounted, the size can be a consideration.
posted 02-03-2014 10:13 AM ET (US)
I'm quite surprised that most if not all of the other
manufacturers don't have tide tables. Garmin has had them
for quite some time (my Garmin GPSMAP 162 that I bought in
posted 02-03-2014 05:45 PM ET (US)
Q isn't as critical with an FM sonar since the pulse is spread over a range of frequencies and the power used is a lot lower. In the days of single frequency pulse sonars Q was critical to get maximum power efficiency, not so with FM. Look at these specs for a Lowrance HDS-7 Gen 2 Touch:
Power Output: RMS (PTP) Max 250W RMS, 30,000W Peak to Peak analog equivalent
The way this 250 W RMS sonar gets to be equivalent to a 30 KW pulse sonar is it uses a long pulse that the electronics (computer) then integrates back into a single short pulse. It's also how a 20' fishing boat can almost have the sonar power of a WW II destroyer...
posted 02-04-2014 10:51 AM ET (US)
Dave--I disagree. The pulse-compression frequency-modulated SONAR units need a low-Q transducer so there is not a big resonance at a certain frequency. At least that is my understanding. I think you are saying that the transducer does not need to be High-Q. That is what I am saying, too. The transducer needs to be Low-Q so it is not very peaked in its response at one frequency.
posted 02-04-2014 01:29 PM ET (US)
I have a Simrad NSS8 which has a touch-screen as well as knob and button controls. I like the touch screen, but I also frequently use the knob and button controls. The combination gives you the best of both worlds. Regarding touch screens specifically, I have found that most of the criticisms are overblown.
Regarding tide information, I believe that is usually a function of the electronic chart cards used with a particular chart plotter. I have a Navionics Gold chart card for my NSS8, and I know for certain it includes tide data. The NSS8 comes with Insight chart data preloaded, and I'm not certain whether or not that includes tide data.
The only other comment I would offer is to buy the largest screen model you can afford. No matter how big you go, you will later wish that you had gone bigger.
posted 02-06-2014 06:24 AM ET (US)
Kevin's observation is very acute. The reason people are making comments to the effect that a Garmin chart plotter can provide data about tides is the cartography and related data available on a Garmin chart plotter is only supplied by Garmin. Garmin has a business model where they are selling the hardware and the software in a bundle. If you get a Garmin chart plotter you will be using Garmin charts, as I do not believe their hardware can be used with any other cartography but Garmin's own.
posted 02-07-2014 07:19 AM ET (US)
"Regarding touch screens specifically, I have found that most of the criticisms are overblown."
Agreed. I went from using an all button controlled Garmin 4208 to an all touch screen controlled Garmin 5208 that is otherwise nearly equivalent to the 4208. I will not go back to buttons if I can help it!
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