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Old 17-10-2017, 13:24   #1
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Current Best Compass?

I've been getting PM's from different people asking advice about electronic compasses. When I was last in the market for a compass, the best one available for less than a grand was the Airmar H2183, which I subsequently bought.

But this is old information. Maybe we need a thread where people who are more knowledgeable and/or have more recent experience can weigh in.
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Old 17-10-2017, 13:26   #2
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Re: Current Best Compass?

My wife uses the compass app on her IPhone.
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Old 17-10-2017, 13:33   #3
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Re: Current Best Compass?

Quote:
Originally Posted by Kenomac View Post
My wife uses a compass app on her IPhone.
And does it work well with your autopilot?
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Old 17-10-2017, 13:36   #4
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Re: Current Best Compass?

Auto has his own compass.
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Old 17-10-2017, 14:07   #5
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Re: Current Best Compass?

https://www.amazon.co.uk/MPU-9250-Co.../dp/B016RJ2ME4

Into a Raspberry Pi. Actually the auto calibrate is having problems, not surprising down below in a steel boat

Quite a bit of change from 1K.
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Old 17-10-2017, 15:38   #6
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Re: Current Best Compass?

One of the key parts of this question is what type of compass is it you're looking for, & what will it's job be. Magnetic, flux gate, gyro, other ??? And for helming, a magnetic compass is fine, & pretty much maintenance free. Well, unless you're doing a circumnavigation, & need it to function in a different hemisphere or zone than it begins it's life in.

Do you need a compass that reads true north, or magnetic north? How about it's update rate in order to work with your other instruments, & or, your autopilot. And is there a good spot near the various neutral axis of your boat to mount something other than a magnetic compass? As if you mount the compass/sensor elsewhere it'll be less accurate, & not work as well in terms of your overall instrument accuracy, & also with the AP.

Plus, if you have a high end AP it may use accelerometers along with the compass to steer the boat well. Which will likely necessitate a more sophisticated (probably proprietary) compass type, & make. Along with backup sensors, & AP & instrument brain modules.
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Old 17-10-2017, 16:13   #7
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Re: Current Best Compass?

Quote:
Originally Posted by conachair View Post
https://www.amazon.co.uk/MPU-9250-Co.../dp/B016RJ2ME4

Into a Raspberry Pi. Actually the auto calibrate is having problems, not surprising down below in a steel boat

Quite a bit of change from 1K.
Thank you for posting this link. I found a more integrated version, BWT901CL for $30 that accepts NMEA GPS inputs and connects to a PC either via Bluetooth, USB or serial. These are made for model airplanes, so the accuracy, update rate, etc. is stated to be about 50x better than than the H2183. I will order one to test how good it actually is.

I think that the phone gyros are likely better than most marine units and most electronic compasses are better than manual magnetic ones. We just need to find a good OEM unit that outputs NMEA, otherwise I need to spend another evening with my Python
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Old 17-10-2017, 17:01   #8
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Re: Current Best Compass?

Suunto Handheld Compasses work really well also as a backup for your GPS etc

http://www.suunto.com/en-US/Products...10-SH-Compass/

Suunto Arrow-30 NH Compass - Ergonomically shaped compass
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Old 17-10-2017, 17:32   #9
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Re: Current Best Compass?

The little Suunto hand bearing compass is expensive ($65) but lets you superimpose a vertical line, the bearing to it, and the reciprocal bearing on your scene by using it with both eyes open. But, for my steel boat, the only compass that is adequately responsive for steering is the flux gate up the mast that feeds the autopilot. No GPS compass responds until you are well off course, and I gave up on trying to compensate a magnetic with a steel bulkhead about three inches in front of it.

The problem with compasses and circumnavigations is dip. The North magnetic pole is well below the surface of the earth, and when you get much below the equator a compass balanced for the Northern Hemisphere starts telling you where Down is.
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Old 17-10-2017, 17:55   #10
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Re: Current Best Compass?

I don't have a lot of sea time with it yet but the new Simrad/B&G Precision 9 rate compass has great specs and gets strong reviews.
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Old 18-10-2017, 11:27   #11
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Re: Current Best Compass?

Based on my research from last night, it seems that modern electronic compasses are all based on these small 9 degrees of freedom MEMS chips. The best known is the Intersense MPU-9250 ($9 from Amazon) but there are others such as the BNO055 and the LSM9DS1. The idea here is that you take the sensor and use a Raspberry to fuse, average and calibrate the data, then format it in NMEA 0183 to feed into the chartplotter. The weak point of these chips is that the magnetometer is relatively noisy but the rate of change is amazing. All told, a well configured system should be in the +/- 2 deg of accuracy which is better than a typical fluxgate and the refresh rate can be very high, up to 200 Hz (clearly a lower rate should be used to feed most chartplotters). In terms of usability such a system is problematic. For example, you need to enter commands on the Raspberry to calibrate and align the sensor. Thus my pecking order to answer the original question, best to worst:

1. KVH Azimuth 1000 ($600) - replaces the binnacle compass, 0.5 deg accuracy, 10 Hz, calibrates automatically as you go, easy to use and setup.

2. All vendor compasses, incl. Raymarine EV-1, H2183 based systems from Garmin and Simrad, etc. (~$600 retail), around 1-2 deg accuracy - less accurate than the KVH but still very good, some calibrate automatically, others require the vendor chartplotter. Note the H2183 is an 8-axis device.

3. Home made system based on the Intersense MPU-9250 ($50 total) - requires programming, difficult to calibrate but should be ideal for MARPA. Really makes more sense if one wants to play with OpenPlotter and fuse many sensors on the Raspberry. Easy to modify and upgrade, eventually someone will write an autocalibration code similar to the KVH approach. It needs to have the Raspberry powered all the time.

4. Vendor systems based on a fluxgate with 1-dimensional gyro compensation. A prime example will be the Raymarine Smart Heading Sensor. Old by today's standards.

5. Plain old fluxgate compass - what most autopilots use today.

In addition, I found a couple of real inertial navigational units (although you can use the MPU-9250 chip above to calculate the position based on the accelerometer output, it is not accurate enough for a small boat). These are pricey but I believe the best option for a recreational sailor today:

A. KVH DSP-17xx is an IMU with fibre optic gyros, excellent for MARPA (~$4,000)

B. Intersense NavChip (~$4000) MEMS based but when coupled with a magnetometer and a Raspberry can provide properly stabilized output.

Regards,
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Old 18-10-2017, 12:11   #12
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Re: Current Best Compass?

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Originally Posted by Pizzazz View Post
Easy to modify and upgrade, eventually someone will write an autocalibration code similar to the KVH approach. It needs to have the Raspberry powered all the time.
That's actually already written (by boat_Alexandria I think) and implemented, Pi draws about 0.3A , outputs signalk & NMEA over wifi along with anything else coming in.

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Old 18-10-2017, 20:40   #13
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Re: Current Best Compass?

From the discussion I infer you are looking for an compass + attitude sensor unit, not just a compass?

How about the Thrane LT-500 AHRS then?

http://thrane.eu/wdpress/index.php/lt-500-ahrs

Specs similar / better than Precision-9 (which I have and am happy with), with possibility of setting up and calibrating directly on the unit without the need for a compatible chartplotter, and additional baro / temp sensors.

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