Radar....When to buy

[tome]

Re: Raymarine rate gyro....

If you want a really good electronic compass then the best I've discovered is the Honeywell HMR3000 available from TDC Ltd for around £450.

We use a more expensive unit for survey, but this compass outperforms it with excellent heading stability over a wide range of pitch and roll. It provides outputs up to 20Hz, easily fast enough to stabilise a radar or AP. It's actually a 3 axis magnetometer and smart processor rather than a conventional fluxgate.

 

[pvb]

Re: Raymarine rate gyro....

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No I didn't mean Raymarine's rate gyro.

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I didn't suggest you did - I was referring to BlueChip, whose post you'd replied to.

Agree that an integrated compass correction system, such as you have, might be the best technology. But interestingly, Raymarine make no recommendation about mounting their add-on rate gyro (Smart Heading System) close to the fluxgate compass, so I imagine they've found it doesn't matter too much on a boat.

 

[Oldhand]

Re: Raymarine rate gyro....

I failed to come up with that one when I was searching for a high speed heading data output device. It sounds good and probably more worth the money than Raymarine's expensive system. However, I wonder if leisure radars can actually process heading input any quicker than 10Hz, this being Raymarine's recommended input.

Another problem with having an autopilot indepedent heading sensor for radar stabilisation, is that the 2 sources are unlikely to give the same output all the time. One could thus be confused by having 2 different sets of heading data displayed and be left wondering which one is correct. It was in order to avoid this that I decided upgrading my Simrad autopilot system was the sensible way to get the heading data required for radar stabilisation.

However, having gone what might be considered an unusual route, I wanted hard evidence that I had achieved 10Hz output of the NMEA "HDG" word. I connected the serial port of a laptop to my system and ran a utility called "NMEA Tool". After logging 5 seconds of data, I counted the number of HDG words in the log file produced and found exactly 50. I wonder if this sort of check is made on many installations or whether people have more trust than me?

 

[pvb]

Probably worth more money....

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probably more worth the money than Raymarine's expensive system

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If the Honeywell system tome recommended is "around £450" as he said, isn't that roughly the same as the Raymarine system? On that basis, you probably can't call the Raymarine system "expensive". One advantage of the Raymarine system is that it can be controlled via SeaTalk from the radar/plotter display to linearise the compass automatically. How would the average boaty achieve this with a third-party system?

 

[tome]

Re: Raymarine rate gyro....

The Honeywell output can be limited to 10Hz (or less if required), and it outputs the NMEA sentences required by APs and radars. Agree about avoiding 2 heading sensors - it's difficult enough to find a good location for one!

Because my small business unit designs and tests nav systems, we have some powerful tools in our lab. We can precisely timestamp all data streams so that not only can we see the rates, we can also see their consistency and can accurately de-skew an array of instruments from different suppliers.

I'm not going to knock Raymarine's products as I find them generally good, but I do stand by my recommendation of the Honeywell compass. We've yet to do a field test, but results have been superb in the lab. I have one fitted to my boat for data collection but not yet used to stabilise radar or control AP. It's a next generation product up from a rate gyro or fluxgate IMO and I'm not going to bore you with any more detail /forums/images/graemlins/wink.gif

 

[tome]

Re: Probably worth more money....

You need to connect a laptop to carry out the calibration or to alter data rates or sentences using their supplied software. It uses flash memory so won't forget settings.