Why GPS compass for 500 GT vessels only


#21

I don’t understand why larger vessels are not using Inertial Navigation. That is well proven tech that would solve a lot of potential problems, spoofing, jamming, etc.


#22

Here’s another one, sells for 9126 USD.

image

I wonder if this claim is accurate?

Its heading is more accurate than high end gyrocompasses costing ten times the price and is continuously reliable unlike GPS compass systems.


#23

Maybe, since “more accurate than” is a very diffuse term. I suppose you could postulate a usage case where gyro drift would be expected (like intermittent power supply), and say that this one is now more accurate since it’s able to pick its heading back up from satellites. The stated heading accuracy of 0.1 degrees is impressive for a satellite compass, but not so impressive for a gyro.

However, that whole site has suffered severe defacement by marketeers. After mouthfuls like “sophisticated fusion algorithm”, “supports all (…) future satellite navigation systems” and “safety oriented real time operating system”, I now suffer a level of queasiness that can’t be ascribed to the swell on our port quarter.

Seriously, who thought it was a good idea to inject marketing BS between engineers?


#24

I guess I should retract my statement, but those “gyros” would seem to have little to do with an actual “gyro compass” like the ones on actual ships. The Raymarine autopilot on my home (yott) has a couple of those to compensate for roll and pitch motion, but I don’t consider it anything like a true gyro compass. (and the implementation is far from perfect)


#25

That was my thinking as well but evidently that’s not industry standard - Here is an interesting paper: Gyroscope Technology and Applications: A Review in the Industrial Perspective (pdf)

The term “gyroscope”, conventionally referred to the mechanical class of gyroscopes, derives from the Ancient Greek language, being the Physics of the “precession motion”, a phenomenon also observed in ancient Greek society [1].

Many classes of gyroscopes exist, depending on the operating physical principle and the involved technology. Gyroscopes can be used alone or included in more complex systems, such as Gyrocompass [2], Inertial Measurement Unit [3], Inertial Navigation System [4] and Attitude Heading Reference System [5]. In this paper, a review of the more commercially diffused classes of gyroscopes is presented. In particular, mechanical gyroscopes (Section 2); optical gyroscopes (Section 3), including Fiber Optic Gyroscopes (FOGs) [6–8] and Ring Laser Gyroscopes (RLG) [9,10]; and Micro-electromechanical system (MEMS) gyroscopes [

gryo


#26

Hmm… looking along the bottom “bias stability” scale of that chart, I don’t see much use for a “gyro” with values above 1-2 degrees per hour for long-term navigation use. compensation for motion, yes - but not as a heading reference unless it’s just short-term stabilizing something with better long-term performance (like a magnetic or GPS compass). I am impressed with the GPS compass’ I see here, though - that tech looks useful to me, and I can see how advancing technology will make them better & cheaper.


#28

I take that to mean more then one type sensor and a Kalman filter or similar.

In any case if the GPS compass combined with MEMS data is 10,000 USD and a small mechanical gyro is 20,000 USD I would think the extra 10,000 is a small part of the total budget. Assuming the boat is capable of providing an adequate power supply.


#29

The Furuno Sat Compass is $4000 with small installation and start up cost and virtually no maintenance.

The cheapest USCG approved gyro I have seen, cannot remember which brand or model, is $16,000 plus significant installation, start up, and maintenance costs. By the time it’s running it will be over $20,000.

Several times I have seen small companies with tight budgets waste $10,000 repairing, or worse, trying to repair old gyros. After that, they don’t want to hear about anything except a magnetic compass. Once the cost driven switch to magnetic is made, the north up radar, arpa, and so on, no longer function without a true north heading input. Not to mention, that the magnetic compass takes on a huge usually unknown error as soon as you hip up to a barge. It’s much better to just switch to the sat compass in the first place rather than to try to repair an old gyro.


#30

The GPS compass is $4000 plus the risk associated with the unreliable GPS signal. If that risk is considered acceptable than it just a matter of comparing cost in which case the pure GPS system is clearly lower cost. No doubt about that.


#31

I have never been on a yacht with a true GPS compass. Plenty of them - actually almost all of them - will have a GPS heading display somewhere. For a slow boat in current, the heading can be quite a bit off where the bow is pointing!
10 Hz fluxgates are a thing if you want the MARPA/ARPA to work worth a crap, but they are as good as the installation and calibration. If you put the thing right next to a locker where people put steel tools in and out… maybe not so good :frowning:


#32

Sounds like COG not HDG.


#33

Yes exactly. The standard GPS has no idea what is what until it moves.


#34

If the marketing hype is true then why haven’t they gone for FAA and USCG approval?


#35

It would be nice to quit resetting the gyro every so many minutes. For airplanes with vacuum gyros you get redundancy issues, you can only switch so much stuff from vacuum to electric until you get a requirement for standby power or dual busses that drive the cost up. I also think most pilots would be pretty nervous about losing the compass if there is a GPS issue. For those who don’t know, flying off a mag compass is a huge PITA.


#36

I don’t know maybe the claims are correct in some applications. @Klaveness mentioned vessel motion, maybe vibration would limit effectiveness?

I would think any of these issues could be overcome with a hybrid system and software filtering but the ceiling on costs is the low-end mechanical gyro.


#37

Here you go, some expensive solutions to your problems:

https://www.km.kongsberg.com/ks/web/nokbg0240.nsf/AllWeb/1CC97340CD83F369C1257C8D002E9F28?OpenDocument

Or

https://www.km.kongsberg.com/ks/web/nokbg0240.nsf/AllWeb/1466922232A64232C125819B003BB2DA?OpenDocument

With a DPS i4 all the satellites have to fall out of the sky for it to fail. If some of the sailing/working dinosaurs wonders.


#38

cost…
INS should be the basis of all DP installations to help prevent pos refs that gang up to vote others out. INS is the only device that can you tell you what is really happening at the instant you get a fault.
Lots have been installed on DP rigs that go to the parts of Brazil that have bad scintillation every arvo

PS all the stuff in a toy drone cost $100 and its 3 axis gyro/ins etc, lots of room for prices to comes down


#39


#40

On this thread mariners with practical experience with GPS compass have brought up the problem of temporary loss of a clean GPS signal. But this post is just marketing fluff.

Do you have anything more substantial? Cost/reliability comparisons, regulatory issues?


#41

I guess we need to know if a postilion jump also effects a gps compass?

It will still have the same issues at a platform so not reliable there