Furuno SCX 20 Satellite Compass

[Dockhead]

Anyone have experience with this device? I'm trying to improve heading data for pilot, MARPA, and radar overlay. Kind of tired of magnetic compass issues.

[slug]

I’ve seen them on super yachts as a gyro substitute

Never used one

Whats wrong with the new generation autopilot compasses ?

[Dockhead]

Originally Posted by slug

I’ve seen them on super yachts as a gyro substitute

Never used one

Whats wrong with the new generation autopilot compasses ?

Never ending search for more accuracy more stability.

[Q Xopa]

Originally Posted by Dockhead

Anyone have experience with this device? I'm trying to improve heading data for pilot, MARPA, and radar overlay. Kind of tired of magnetic compass issues.

Nope haven't used em. At a quick glance they sound pretty good. I know you have been looking for something along these lines for a bit. How do the performance specs stack up?

[Nicholson58]

We installed the electronic rate compass required with our Simrad suit of chart plotter, broadband radar, and autopilot. It is reliable and repeatable. Since it is aligned to the vessel it registers the angle of the boat centerline which shows as a crab angle on the avatar of the chart plotter. The GPS gives true course over ground at the plotter including leeway and drift from currents. Our Simrad autopilot can be made to steer by GPS COG, rate compass, or to a distant GPS point. It can be made to reference either true or magnetic north. Compass variation in the Caribbean is big. The numbers shown by all of these various devices never agree. The only possible exception is dead down wind motoring with no current. The point is that you need to learn how to make these tools work for you. I also keep paper charts nearby.

[Tugwit]

I just installed an SCX20 a couple of weeks ago to replace an infuriatingly inaccurate Aimar H2183 (dunno why the otherwise well-regarded 2183 never worked properly on my boat--maybe the 2 ton cast-iron keel ).

Due to an ongoing hatch replacement project, I haven't been away from the dock to perform a sea-trial yet, but the heading data provided by the SCX20 is spot on for the position of my boat in its slip. Not so for the 2183.

After some initial difficulty, I used my Actisense NGT gateway to run the Furuno SC Setting Tool to provide the necessary configuration coordinates for the SCX20. While I don't have a particularly large N2K network, it was necessary to disconnect many of the devices from the network to provide sufficient bandwidth for the Setting Tool to work. Once that was done, however, the tool worked well. (I've never experienced a similar problem with configuration software from other vendors, e.g. Airmar Weathercaster, Maretron N2KAnalyzer, etc, but there you have it...)

Hopefully, I'll be out on the water in the next couple of weeks and can provide a more comprehensive report later. I expect to use the heading data for better autopilot control and sailing performance data--not so much MARPA or fathometer corrections....

[TBW]

Have scx21 for 0183. Got it when first available. Perfect.
Cross track usually 1 to 2 degrees. 50 x 24 . 50 tons. 7 knots.
Many problems went away.
Get it.
Always best to go with Furuno.
TW

[Oceanride007]

I have a Raymarine set up with one of their EVG1. My problem is that it appears got quite a bit of Deviation, may be up to 10 deg. Due to my boat being steel I suppose and there appears to be no adjustment available for it.
It only matters when trying to get data for polar diagram.
Think such a devise as the SCX may solve my problem, or is there another method/devise. Apologies for thread drift.

[Dockhead]

Originally Posted by Tugwit

I just installed an SCX20 a couple of weeks ago to replace an infuriatingly inaccurate Aimar H2183 (dunno why the otherwise well-regarded 2183 never worked properly on my boat--maybe the 2 ton cast-iron keel ).

Due to an ongoing hatch replacement project, I haven't been away from the dock to perform a sea-trial yet, but the heading data provided by the SCX20 is spot on for the position of my boat in its slip. Not so for the 2183.

After some initial difficulty, I used my Actisense NGT gateway to run the Furuno SC Setting Tool to provide the necessary configuration coordinates for the SCX20. While I don't have a particularly large N2K network, it was necessary to disconnect many of the devices from the network to provide sufficient bandwidth for the Setting Tool to work. Once that was done, however, the tool worked well. (I've never experienced a similar problem with configuration software from other vendors, e.g. Airmar Weathercaster, Maretron N2KAnalyzer, etc, but there you have it...)

Hopefully, I'll be out on the water in the next couple of weeks and can provide a more comprehensive report later. I expect to use the heading data for better autopilot control and sailing performance data--not so much MARPA or fathometer corrections....

Thanks. That sounds encouraging. Please post updates when you've been out with it.


I am changing for exactly the same reason -- an H2183 which is just not as good as it is supposed to be.

[Dockhead]

Any other opinions on the SCX20 vs other compasses?


The price is about $1000 in the U.S. which is near the price of the cheapest GPS compasses previously, and less than half of the cost of the classic SC33.



The Furuno propaganda makes it look awfully appealing:


https://furunousa.com/en/products/scx20


But I don't know how it stacks up in real life. They claim 1 degree static and 0.5 degree dynamic accuracy; the H2183 claims 2 degrees dynamic accuracy, but I don't believe I have seen that kind of performance.

[kokajambo]

My world is turning upside down with you guys.
I always thought that solid-state compass+accelerometer (to compensate heading for roll) is _the solution_ to inaccurate heading data from GPS.
The reason being that the magnetic field of planet Earth is just about as big and as stable a thing as they get...
There are of course local magnetic abnormalities caused by geological features and Tugwit's 2ton iron keel, but they are compensated for by compass calibration.

Now you talk sattelite compass being more accurate, I can't help but think there is something wrong with your regular compass. It must be either faulty or mounted in a weird place where it's shielded from Earth's magnetic field, or not properly calibrated...

I know I sound like a broken calibrecord, but have you carefully calibrated your (G)H2183 following all of instructions in the manual?
It must be done after it's installed in its permanent place on the boat!
Then, you must do it again if you move your boat to a different geographic location! (there is no specific distance threshold, basically far enough that it starts being inaccurate).

[tanglewood]

I can't speak to this particular device, but I have more faith in Furuno to get it right than any of the other vendors.


I do have first hand experience with a couple of other sat compasses, and I would never consider anything else. I do still have a magnetic rate compass as a backup device, but it's only there if the sat compass fails.


The benefits, as I see them, are:


- No more magnetic interference, either from things external to the boat, or soup cans rolling around is a drawer near the compass, or electro-magnetic interference when a large appliance gets turned on, etc.


- It give true heading, and isn't dependent of a variation almanac that gets out of date.


- The heading and position and rate of turn are much more precise that with a rate compass.


- The lower end models like the SCX20 are about the same cost as a quality rate compass plus a good GPS, so why not....

[Statistical]

Originally Posted by kokajambo

My world is turning upside down with you guys.
I always thought that solid-state compass+accelerometer (to compensate heading for roll) is _the solution_ to inaccurate heading data from GPS.
The reason being that the magnetic field of planet Earth is just about as big and as stable a thing as they get...
There are of course local magnetic abnormalities caused by geological features and Tugwit's 2ton iron keel, but they are compensated for by compass calibration.

Now you talk sattelite compass being more accurate, I can't help but think there is something wrong with your regular compass. It must be either faulty or mounted in a weird place where it's shielded from Earth's magnetic field, or not properly calibrated...

I know I sound like a broken calibrecord, but have you carefully calibrated your (G)H2183 following all of instructions in the manual?
It must be done after it's installed in its permanent place on the boat!
Then, you must do it again if you move your boat to a different geographic location! (there is no specific distance threshold, basically far enough that it starts being inaccurate).

A normal GPS receiver is pretty poor for heading accuracy but the Furuno SCX 20 is not a regular GPS receiver it is a GPS compass. A GPS compass uses two or more GPS antennas placed a fixed known distance apart to do detailed comparative analysis of the received signals which allow the built in processor to compute in real time the pitch, roll, and heading.

They are pretty much the gold standard for heading accuracy with no downsides beyond cost. 15 years ago they were around $30,000. Five years ago around $5,000. Now the SCX 20 is $1,000.

[Tugwit]

Originally Posted by kokajambo

My world is turning upside down with you guys.
I always thought that solid-state compass+accelerometer (to compensate heading for roll) is _the solution_ to inaccurate heading data from GPS.....

...I know I sound like a broken calibrecord, but have you carefully calibrated your (G)H2183 following all of instructions in the manual?).

Well, let's see if we can get your world right side up!

First of all, a single GPS can provide you with a sort-of heading--Course over Ground (COG), which is the direction that the boat is actually traveling affected as it is by current and wind. Heading, however, is the direction that the bow is pointing regardless of current and wind. If you wish to accurately assess leeway (in general, the difference between heading and track)--whether caused by current, wind, or both, you need both measurements. So COG from GPS is not inaccurate--it's just not heading.

Heading is traditionally measured by a compass carefully aligned with the vessel centerline (i.e. the bow direction). Magnetic compasses (either old school or electronic) respond to the earth's magnetic field and must be compensated, as you say, to account for local ferrous/magnetic influences. Still, there is usually a residual inaccuracy which is tabulated in a deviation table so that the skipper can apply the appropriate correction for a given course and know in which direction the vessel's bow is actually pointing.

I like compasses. I have six: two permanently mounted magnetic compasses mounted on each side of the cockpit, two hand-bearing compasses, an Airmar H2183, and, now, a Furuno SCX-20.

The H2183 is an electronic magnetic compass that measures heading and feeds data to the chartplotter (and autopilot, etc.) so that the little icon that represents your boat points in the appropriate direction. I tried to scrupulously follow Airmar's installation instructions--mounted the compass in the center of the boat and "low", but as far "away" from the 2-ton cast iron keel as I could--about 5 feet (Airmar simply says "away", but doesn't say by how much except 1 foot away from another magnetic compass).

I also scrupulously followed Airmar's calibration instructions--many times, in fact. I've been out at 5 in the morning on high tides and low tides, not a breath of wind, and ran 180-degree/minute circles until my crew got dizzy and threatened to throw-up. I've run so many circles in the local bay that the boys in the club bar were taking bets as to whether I'd lost my rudder or lost my mind. To avoid any local magnetic anomaly, I've run calibration circles in half the bays between Olympia and Cape Scott. No joy. I've never been able to reduce the deviation to less than 15 degrees on some courses.

As a result, the vessel icon on the chartplotter often appears as if I'm crabbing one way or the other--which is disconcerting when you're trying to assess and manage the CPA to another vessel in the fog. It drives me nuts.

The SCX, however, measures heading without using the earth's magnetic field. Instead, it uses signals from GPS/GNSS satellites. As I understand, it effectively measures the subtle time difference between arrival of a GPS/GNSS signal at two independent receivers affixed to a boat but separated by some distance, and, through prodigious calculations, computes how the boat must be oriented (heading) to observe that time difference because it knows the location/direction of the satellite that sent the signal.

As I understand, the SCX actually has four independent GPS/GNSS receivers and performs the above calculations repeatedly, using different pairs of receivers, and using whatever GPS-type satellites (GPS, GLONASS, Galileo, QZSS) you can "see", depending on where you are in the world. Really, pretty amazing.

So far, I have only limited experience with the SCX, but it has been outstanding. I've run several charted ranges in the area in calm conditions and my displayed heading is always within 1 degree of the published range--a difference so small that it's more likely due to steering error than instrument error. The vessel icon on the chartplotter nicely comports with the reality that my eyes perceive, and, with accurate extension lines for heading and COG, I get a very good sense of what the current is doing when transiting through, for example, our local Tacoma Narrows.

So far, so good.

Ultimately, I hope to use it to accurately assess leeway under various sailing conditions and improve my VMG. Sadly, my use will likely not explore and take advantage of other advertised capabilities of the SCX such as "heave" to stabilize the bottom image in fishfinder/sounder applications or improving MARPA performance using Radar....

[Breaking Waves]

Some time ago I've used two (different models on different vessels) of the older furuno sat compasses - primarily installed for up in the north (near magnetic pole where the fluxgates started to have trouble) but also nice in the south. They both worked very well. I do not have any experience with the most recent models (20 and 21).