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Old 25-05-2018, 21:20   #1
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GPS-Hdg Sensor Shoot-Out

I need to replace a failed N2K gps antenna and I'd like to take the opportunity to get another heading sensor at the same time ( I have a Furuno PG500 right now).


The two candidates are a Simrad HS60 vs Airmar WX200 (both have equivalents under different brands). Both have 10Hz GPS's and that's all I care about on the gps front. I am really interested in understanding the quality of the Heading output from these as it must be good enough for autopilot, radar overlay and ARPA/MARPA. I have reviewed the N2K Heading output pgn's and both are equivalent, but I don't know how to make sense of the gyro and accelerometer differences between the two or how to assess the real quality of the Heading outputs. Can anyone help me with this?


(The weather data from the WX200 would be nice, but I wouldn't value this over an inferior Heading accuracy. If Heading accuracy is equal, the WX200 would win the shoot-out for me. Both are around the same cost. The vessel is a 55' motor boat....antennae are mounted on flybridge hardtop, not up a rag stick)
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Old 26-05-2018, 01:04   #2
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Re: GPS-Hdg Sensor Shoot-Out

There is a difference between a heading sensor and a position (GPS) sensor. The GPS can give you SOG (speed over ground) and COG (course over ground) and these are useful but not accurate enough to calculate true heading and rate of turn even at 10 Hz update. The problem is that there is jitter in the GPS position calculation which prevents the sensor from giving you stable heading and rate of turn indications. My experience is that if you want good radar/chart sync and MARPA you need to have all six inputs (position, SOG, COG, speed through water, heading and rate of turn).

Heading at 10 Hz is most important, rate of turn is the least important. Fast GPS update is better but not essential. In terms of heading sensors, here are your options:

1) Raytheon Standard 22 Gyro Compass. A real gyro compass, the gold standard for larger boats. Runs on 24V, start up time in hours, requires periodic maintenance, consumes a lot of current. Static accuracy is 0.1 degrees/sec, dynamic is 0.4 degrees, up to 50 Hz update speed. A total overkill for a recreational boater but sometimes you can find them used on ebay for reasonable prices. List price is more than $10K. Calibration is a pain.

2) KVH fluxgate stabilized AutoComp 1000. This can be had for as low as $200K on ebay, retails for around $700, heading accuracy is 0.5% static. I used on of these and I am very pleased with the performance. 10 Hz update but only nmea 0183. Self calibrating.

3) Airmar H2183 solid state heading sensor for about $600. Static accuracy is 1 degree, dynamic is 2 degrees, up to 20 Hz output. Great sensor with rate of turn output, resold by Raymarine, Garmin, Simrad, etc.

4) Fluxgate with a rate gyro stabilization. Output at 10 Hz. Performance is similar to the Airmar but calibration is time consuming. ~$200 on ebay.

5) Regular fluxgate sensor at 2 Hz output. Plentiful ebay supply at ~$100. OK fo autopilot, not good for MARPA.

6) Garmin SteadyCast heading sensor, 10 Hz output, 3% static accuracy, $120 new from online suppliers. Not that useful given the poor accuracy.

In addition to the accuracy, the better compasses such as the Raytheon and the KVH have adjustable damping settings for various sea state conditions.

Good luck with you search.

SV Pizzazz
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Old 26-05-2018, 01:53   #3
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Re: GPS-Hdg Sensor Shoot-Out

Simrad HS60 is a GPS compass -- not comparable in any way to the fluxgate in the WX200.

Go with that for sure if you want accurate heading data.

Accuracy of heading data is one of the most important bits of data -- essential to good autopilot performance, radar overlay, MARPA, radar navigation.

I've been dreaming about a GPS compass myself for a long time, and am seriously tempted by the HS60.

On top of all that, the HS60 gives heave data. It's light years ahead of the WX200.
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Old 26-05-2018, 02:09   #4
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Re: GPS-Hdg Sensor Shoot-Out

Pizzazz: thanks for your interest, but you may have missed that I am specifically looking for a GPS+Hdg sensor...not just Hdg. I understand the difference between the two...I want both!
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Old 26-05-2018, 02:09   #5
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Re: GPS-Hdg Sensor Shoot-Out

I don't know where you're based, but www.jgtech.com/shopc.htm has the Airmar GH2183 GPS/heading sensor on offer at £129 at the moment.
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Old 26-05-2018, 02:11   #6
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Re: GPS-Hdg Sensor Shoot-Out

HS60 for sure. As Dockhead said it is a GPS compass.

you'll notice a big difference with your auto pilot, especially if you have a metal boat.

I wish i could justify one.
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Old 26-05-2018, 02:19   #7
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Re: GPS-Hdg Sensor Shoot-Out

Quote:
Originally Posted by hoolie View Post
I don't know where you're based, but www.jgtech.com/shopc.htm has the Airmar GH2183 GPS/heading sensor on offer at £129 at the moment.
That's not a GH2183, but rather the G2183 without heading sensor. The GH2183 is £579.

The G2183 is an obsolete unit which does not receive GLONASS or Galileo. Not recommended when you can buy a Simrad GS25 for just a little more.

But in any case, the OP was looking for combined heading/position. The GH2183 has what used to be the best heading sensor for less than $2000. I have the heading only version. But there has been a lot of progress since then so no way is the GH2183 worth £579 when you can get the HS60 for less than £700.

I guess I need to sell my H2183 while anyone still wants it.
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I behold from the beach your crooked inviting fingers,
I believe you refuse to go back without feeling of me;
We must have a turn together . . . . I undress . . . . hurry me out of sight of the land,
Cushion me soft . . . . rock me in billowy drowse,
Dash me with amorous wet . . . . I can repay you."
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Old 26-05-2018, 02:25   #8
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Re: GPS-Hdg Sensor Shoot-Out

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Simrad HS60 is a GPS compass -- not comparable in any way to the fluxgate in the WX200.

Go with that for sure if you want accurate heading data.

Accuracy of heading data is one of the most important bits of data -- essential to good autopilot performance, radar overlay, MARPA, radar navigation.

I've been dreaming about a GPS compass myself for a long time, and am seriously tempted by the HS60.

On top of all that, the HS60 gives heave data. It's light years ahead of the WX200.

Dockhead...thanks for that. You are right that the HS60 determines heading from maths applied to its two gps antennas vs the WX200's fluxgate compass...BUT with the WX200 up on the flybridge hardtop and so well away from ferrous and RFI interference AND with its identical accuracy specs, I think the comparison is valid. For the same reasons, perhaps I should have added the Airmar GH2183 to the mix. I admit I'm attracted by the 'magic' of the gps compass....but the WX200 has all that interesting/fun 'weather' data. I wouldn't value heave data....I think that is only relevant to fanatical fisherfolks.
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Old 26-05-2018, 03:43   #9
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Re: GPS-Hdg Sensor Shoot-Out

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Originally Posted by aquabelle View Post
Dockhead...thanks for that. You are right that the HS60 determines heading from maths applied to its two gps antennas vs the WX200's fluxgate compass...BUT with the WX200 up on the flybridge hardtop and so well away from ferrous and RFI interference AND with its identical accuracy specs, I think the comparison is valid. For the same reasons, perhaps I should have added the Airmar GH2183 to the mix. I admit I'm attracted by the 'magic' of the gps compass....but the WX200 has all that interesting/fun 'weather' data. I wouldn't value heave data....I think that is only relevant to fanatical fisherfolks.
I can't give you a definitive answer since I've never used the HS60, but the advantages of satellite compasses go far beyond lack of interference -- they are supposed to be more accurate and stable, and since they measure true heading, don't need to compensate for variation in order to do radar nav.

Accuracy and stability of heading data makes a dramatic difference in pilot performance, marpa, radar overlay, radar nav. AFAIK, the WX200's compass is not even navigation-grade. So in my opinion it's a bad idea to settle for a much worse compass just to jam in weather function which can easily be provided in a separate unit.

So if I were you, I would start with the best compass you can afford, and combine it with whatever other functions can be added without compromising that, then adding a separate unit for anything which can't be beneficially combined.

For wind, weather, position, and heading, I would probably do something like HS60 + Maretron WSO100 or the WX100 (or 110 or whatever the simple one is called).
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Old 26-05-2018, 08:41   #10
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Re: GPS-Hdg Sensor Shoot-Out

Quote:
Originally Posted by aquabelle View Post
Pizzazz: thanks for your interest, but you may have missed that I am specifically looking for a GPS+Hdg sensor...not just Hdg. I understand the difference between the two...I want both!
I see you want a combined unit but my point was that the HS60 and most cheap GPS compasses do not give you the accuracy that you need. The HS60 is spec'd at 2 degrees heading accuracy which is just not good enough. It has dual antennas but they are mounted very close to one another and the jitter in the position calculation prevents you from getting good accuracy. Not to mention that the slower you go, the less accurate it is.

There are GPS compasses that have two antenna's spaced apart (for example, the VN-300, search it on the web, antennas need to be mounted at least five feet apart) that give you great heading (0.1 degrees static, 0.3 degrees dynamic, comparable to the real gyros plus a built in INS) but they cost $5,000. There is also the HS70 that is about $2000, antennas spaced 1 foot apart, less accurate. I think you would be better off with an H2183 or the GH2183 mentioned.

Look at it this way, a quality GPS sensor (ublock on Amazon for $12, I have one of those) will give you accurate position at up to 200 Hz if you could take it over a fast nmea/serial port. But lots of jitter in the position. A cheap MEMS 9-axis sensor will give you 3D orientation for less than $50, also with lots of jitter in the orientation. If you combine these with the proper algorithms you get the HS60 but the accuracy drops to 2 degrees. If you want higher quality MEMS you need to buy the GH2183. If you jump to a real dual GPS compass, there are many offerings in the $2,000 range from Simrad, NKE, etc. and you can get sub 1 degree accuracy. If you want gold standard performance, then you need the Raytheon or the VN-300 or equivalent. There is no shortcut to it.

I recommend having two sensors because it is better to mount the heading low, near the center of gravity, while the GPS sensor likes to have a clear view of the sky. Yet, most new GPS sensors are so sensitive that they would work in the bilge with no problem (the ublock above).
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Old 27-05-2018, 00:08   #11
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Re: GPS-Hdg Sensor Shoot-Out

Pizzazz....no argument that there are varying degrees of accuracy between gps compasses. But with hyper-accuracy goes hyper-pricing, as you have indicated. I don't need better than 2degrees RMS accuracy and couldn't afford it if I did. I want an alternative to my Furuno PG500 (aka PG700 if N2K) which performs well most of the time and has dynamic accuracy of 1.5deg...BUT which needs frequent re-calibration, which is awkward given it is buried in the vessel's bowels where it is supposed to be.

So for an equivalent accuracy without the hassles of a fluxgate, I think the HS60 is the go. The cost is acceptable given I need to replace the Furuno GP-330B that has died anyway and the HS60 gps is better all-round.

You are also right that the disadvantage of a fluxgate-based integrated GPS/Hdg sensor is that it puts the fluxgate component up in the air with the gps, rather than in the bowels down below. That's another + for the HS60 (hdg not fluxgate-derived). Based on the consenus of comments here and on other fora and given I've been offered a good deal on an HS60, that's the way I've decided to go.

Thanks for taking the time to contribute.
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Old 27-05-2018, 04:12   #12
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Re: GPS-Hdg Sensor Shoot-Out

Quote:
Originally Posted by aquabelle View Post
Pizzazz....no argument that there are varying degrees of accuracy between gps compasses. But with hyper-accuracy goes hyper-pricing, as you have indicated. I don't need better than 2degrees RMS accuracy and couldn't afford it if I did. I want an alternative to my Furuno PG500 (aka PG700 if N2K) which performs well most of the time and has dynamic accuracy of 1.5deg...BUT which needs frequent re-calibration, which is awkward given it is buried in the vessel's bowels where it is supposed to be.

So for an equivalent accuracy without the hassles of a fluxgate, I think the HS60 is the go. The cost is acceptable given I need to replace the Furuno GP-330B that has died anyway and the HS60 gps is better all-round.

You are also right that the disadvantage of a fluxgate-based integrated GPS/Hdg sensor is that it puts the fluxgate component up in the air with the gps, rather than in the bowels down below. That's another + for the HS60 (hdg not fluxgate-derived). Based on the consenus of comments here and on other fora and given I've been offered a good deal on an HS60, that's the way I've decided to go.

Thanks for taking the time to contribute.
I think you've made a good choice.

I'm not sure why Pizzazz would recommend the H2183 over the HS60 -- does he have experience with both? I have the H2183 and it was the best sub-$1000 heading sensor in its day, but I think time has passed it by. Its nominal accuracy is the same as the HS60 -- 2 degrees in "dynamic" conditions - but nominal accuracy is very far from the only factor which makes a good heading sensor -- it would be like judging cars solely on the basis of how many horsepower they have. Satellite compasses work on entirely different principles from magnetic ones, and they have a whole bunch of serious advantages. I wish I had one myself.
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Old 27-05-2018, 05:54   #13
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Re: GPS-Hdg Sensor Shoot-Out

Looked at the Simrad website to get more information and found there is now an HS70.

I also found some online discussions that the Precision 9 compass can output heave data as well the HS60/HS70 although that feature may be pending a software update.
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Old 27-05-2018, 09:03   #14
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Re: GPS-Hdg Sensor Shoot-Out

I think we are all in agreement about the options vs. price vs.performance. I believe accurate and smooth heading data is more important if you care about smooth chart overlay and MARPA and less so if you just need it for the autopilot. I tried various sensors to optimize MARPA on my E80 display, fluxgate, stabilized fluxgate, H2183 and the KVH 1000 sail compass. The last one was by far the best and cost ~$200 on eBay. The specs also confirm that with 0.5 degrees accuracy. By the way, it also helped that I put a speed through water sensor on the boat. Now my overlay is finally smooth without jumping around.

You may be right that there is not a big difference between the Airmar and Simrad sensors. As I mentioned above, the key though is to have stabilized reading, which means to be able to smooth the heading change in various conditions. You would expect that Simrad sensors would be optimized for navico equipment.

Regarding GPS compasses, it seems that the accuracy depends a lot on the separation of the GPS antennas. It would be interesting to find a solution with two small antennas, one mounted be on the bow, the other on the stern and some software doing the math. You still need a 3D gyro to compensate for roll motion. I would like to think these systems will go down in price. The component cost is less than $100, what is the markup for?
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Old 27-05-2018, 09:57   #15
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Re: GPS-Hdg Sensor Shoot-Out

Quote:
Originally Posted by Pizzazz View Post
I think we are all in agreement about the options vs. price vs.performance. I believe accurate and smooth heading data is more important if you care about smooth chart overlay and MARPA and less so if you just need it for the autopilot. I tried various sensors to optimize MARPA on my E80 display, fluxgate, stabilized fluxgate, H2183 and the KVH 1000 sail compass. The last one was by far the best and cost ~$200 on eBay. The specs also confirm that with 0.5 degrees accuracy. By the way, it also helped that I put a speed through water sensor on the boat. Now my overlay is finally smooth without jumping around.

You may be right that there is not a big difference between the Airmar and Simrad sensors. As I mentioned above, the key though is to have stabilized reading, which means to be able to smooth the heading change in various conditions. You would expect that Simrad sensors would be optimized for navico equipment.

Regarding GPS compasses, it seems that the accuracy depends a lot on the separation of the GPS antennas. It would be interesting to find a solution with two small antennas, one mounted be on the bow, the other on the stern and some software doing the math. You still need a 3D gyro to compensate for roll motion. I would like to think these systems will go down in price. The component cost is less than $100, what is the markup for?

KVH 1000? But that's an ancient, simple fluxgate compass without even any rate gyro compensation. It might be accurate to 0.5% in static conditions, but fluxgate compasses have to be kept exactly horizontal to work, and so they have internal gimbals. The compass on the gimbals has inertia and friction and so you get a really dirty (not only inaccurate, but highly inconsistent) heading data output unless you can compensate the output from the fluxgate electronically with data from accelerometers, which all decent modern fluxgate compasses have nowadays.

But even with a good quality rate gyro (not an actual gyro, but to be more precise accelerometer) compensation, the heading data from a fluxgate compass is still degraded by heel and boat motion. 2 degrees in "dynamic conditions" is CLAIMED for the H2183, but I am sure that this is under good sea conditions and that it's a lot worse than that in rough weather or on a big heel. And like with a lot of instruments -- the most important thing is not the absolute accuracy compared to the Earth, but the consistency of the data. A simple uncompensated fluxgate, no matter how accurate it is in static conditions, will be far worse in realistic, dynamic conditions than one with good accelerometer compensation.

This is one of the huge advantages of satellite compasses -- they are not affected in the same way by boat motion or heel. There is no inertia or friction to compensate for, nothing mechanical. Furthermore, they are not affected by magnetic anomalies and there is no error which comes from compensating for deviation.

So you really can't compare compasses just by looking at the claimed heading accuracy, which is pretty much completely meaningless when you are comparing compasses of different types -- simple fluxgates, two-axis compensated fluxgates, three-axis compensated fluxgates (like the H2183), and satellite compasses.
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