Fluxgate compass

[chrishscorp]

In the process of updating the boats systems currently have a Garmin 126s and a Raymarine autohelm. I have had a good look over the boat but I was told that somewhere on the boat it will need a gyro compass for the auto helm to use to get a heading, is this correct ? and where might it be hidden as I have not seen anything.
TIA



Thread title edited

 

[Sandy]

The best place for it is the centerline of the boat. I'd start there. Mine is under the sink! Not sure if that affects it or not.

 

[LittleSister]

Depends on the model of Raymarine autohelm. Some (e.g. tiller pilots) have an internal one - check the manual.

Your question doesn't make the context clear. Presumably the auto helm works, in which case why do you need to find the compass? There will be wires from it to the autohelm, and which wires they are can be identified with the aid of the manual.

If it doesn't work (because it lacks a compass or compass wiring), what makes you think the boat has one?

 

[Refueler]

GYRO compass ??????

Are you sure ? Maybe you mean Fluxgate Compass which is the usual yacht item.

 

[chrishscorp]

My bad it could be a fluxgate compass.
Updating, the Garmin is going and being replaced with an Axiom 9 and AIS so need to link it all up
The auto helm is a Raymarine ST1000 i think as boat is 32 foot

 

[Refueler]

My bad it could be a fluxgate compass.
Updating, the Garmin is going and being replaced with an Axiom 9 and AIS so need to link it all up
The auto helm is a Raymarine ST1000 i think as boat is 32 foot

The Raymarine ST1000 if its the tillerpilot version - has a Fluxgate compass INSIDE the case .....
ST1000 & ST2000 Cockpit Autopilot Tiller Pilots | Marine Electronics by Raymarine

I believe you can connect an external compass to overcome any problems of errors at helm area.

 

[Sandy]

My bad it could be a fluxgate compass.
Updating, the Garmin is going and being replaced with an Axiom 9 and AIS so need to link it all up
The auto helm is a Raymarine ST1000 i think as boat is 32 foot

We knew what you meant.

 

[chrishscorp]

The Raymarine ST1000 if its the tillerpilot version - has a Fluxgate compass INSIDE the case .....
ST1000 & ST2000 Cockpit Autopilot Tiller Pilots | Marine Electronics by Raymarine

I believe you can connect an external compass to overcome any problems of errors at helm area.

So that is probably why I would not have found one previously, the fun bit will be getting it all to work again.
I currently have the Axiom wired in stand alone so its now a case of just adding bits in to a backbone network. The Axiom manual is about 430 pages long, only 3 pages of the manual relate to loading of the charts, intial impression is lovely clear charts and picture just surprised it cant make me a cup of tea it seems to do just about everything else.

 

[PaulRainbow]

GYRO compass ??????

Are you sure ? Maybe you mean Fluxgate Compass which is the usual yacht item.

Some Raymarine autopilots are fitted with a gyro compass.

 

[PaulRainbow]

So that is probably why I would not have found one previously, the fun bit will be getting it all to work again.
I currently have the Axiom wired in stand alone so its now a case of just adding bits in to a backbone network. The Axiom manual is about 430 pages long, only 3 pages of the manual relate to loading of the charts, intial impression is lovely clear charts and picture just surprised it cant make me a cup of tea it seems to do just about everything else.

The tiller pilot will likely be on Seatalk, the Axiom will be on Seatalk NG (NMEA 2000 with Raymarine cables and connectors). You'll need a Seatalk to Seatalk NG converter kit to get them to speak to one another.

 

[William_H]

Gyro compass? I am guessing that Paul is talking about a gyro stabilised compass. Common on aircraft the directional gyro is stabilised that is automatically aligned to the magnetic compass. Usually a fluxgate compass. The gyro gives a very accurate stable heading data.
A "gyro compass" is a clever device which has no relation to earth's magnetic field. So is good for high latitudes. It is a gyro which aligns itself with it's rotation around the earth. ie aligns with west to east movement. The problem is that they take something like 24 hrs to align them selves and from then on must be continually powered. I wonder now with laser gyros being so common if these problems can be overcome. ol'will

 

[AntarcticPilot]

The Raymarine ST1000 if its the tillerpilot version - has a Fluxgate compass INSIDE the case .....
ST1000 & ST2000 Cockpit Autopilot Tiller Pilots | Marine Electronics by Raymarine

I believe you can connect an external compass to overcome any problems of errors at helm area.

Yes, there is an internal compass but it's in chocolate teapot territory, unless the autopilot is used as a stand-alone piece of equipment. First, it only gives a true heading if the tiller-pilot is connected - and of course, the whole point is that you generally don't use a tiller-pilot all the time; for example, I usually only use mine under engine or to give me a few minutes away from the helm when managing other things. Second, if you have other equipment in the vicinity (I have a command mike for the VHF) it will be affected by stray magnetic fields. If the tiller-pilot is integrated with the rest of your equipment, an external fluxgate compass is essential to avoid erroneous readings when the tiller-pilot is not in use.

 

[Refueler]

Gyro compass? I am guessing that Paul is talking about a gyro stabilised compass. Common on aircraft the directional gyro is stabilised that is automatically aligned to the magnetic compass. Usually a fluxgate compass. The gyro gives a very accurate stable heading data.
A "gyro compass" is a clever device which has no relation to earth's magnetic field. So is good for high latitudes. It is a gyro which aligns itself with it's rotation around the earth. ie aligns with west to east movement. The problem is that they take something like 24 hrs to align them selves and from then on must be continually powered. I wonder now with laser gyros being so common if these problems can be overcome. ol'will

Interesting post ....

Having been a senior Navigating Officer on ships .... one of my responsibilities was to look after the Gyro Compass ..... magnetics as well - but lets stay with the Gyro.
Even the old large Sperry with its sequential shut down / start up routines never took 24hrs to align. I accept it was not instant - but I never had any Gyro take 24hrs .... Anshutz ... Sperry and various others I looked after.

 

[Refueler]

Yes, there is an internal compass but it's in chocolate teapot territory, unless the autopilot is used as a stand-alone piece of equipment. First, it only gives a true heading if the tiller-pilot is connected - and of course, the whole point is that you generally don't use a tiller-pilot all the time; for example, I usually only use mine under engine or to give me a few minutes away from the helm when managing other things. Second, if you have other equipment in the vicinity (I have a command mike for the VHF) it will be affected by stray magnetic fields. If the tiller-pilot is integrated with the rest of your equipment, an external fluxgate compass is essential to avoid erroneous readings when the tiller-pilot is not in use.

Of course if the yacht has an integrated system with compass data input - then of course a Tiller Pilot Compass is insufficient. Which is why there are stand alone Fluxgates such as the Nasa available to provide that data.

The other factor you touch on - is the matter of error caused by any item placed near the tillerpilot that has any magnetic flux. It could be anything from placing an outboard in the locker under / nearby .... even to a smart phone placed next to it ...
Several times my Tillerpilot has had such ... even my bulkhead compass was seen to be offset by a pal placing his 'item' above it under the sprayhood.
BUT one aspect ... if the item in the locker or nearby is constant and there when tillerpilot enabled ... stays there till completion of the tillerpilots job ... the error is of no consequence in fact. The tillerpilot as a stand alone acts on change of direction detected - not on absolute compass direction. If its connected to plotter and receives data - its still working on change of direction.

 

[Refueler]

Some Raymarine autopilots are fitted with a gyro compass.

I know and have used Raymarine Autopilots on ships that work WITH the Ships Gyro. I can only assume that an Autopilot fitted with its own Gyro must be on a large yacht ...

 

[PaulRainbow]

There are differences between the equipment use by aircraft and that used by ships, add to that the fact that leisure marine "gyro" compasses are not always true gyro devices.

The Raymarine one, for instance, is actually a "rate stabilised fluxgate compass", as alluded to by Will, above. The S series Raymarine autopilots had a model that was suffixed with a "G" (G2, G3 etc) and Raymarine referred to these as being the "Gyro" version. It was, in fact, a rate stabilising device for the external fluxgate compass. It's primary function was to provide yaw and pitch data to the ACU to make the fluxgate more stable.

The current "heading sensors" marketed by Raymarine, Garmin, Navico etc are a single package device, with provides a stabilised heading to the ACU and other instruments by taking into account roll, pitch, yaw and acceleration.

 

[Refueler]

There are differences between the equipment use by aircraft and that used by ships, add to that the fact that leisure marine "gyro" compasses are not always true gyro devices.

The Raymarine one, for instance, is actually a "rate stabilised fluxgate compass", as alluded to by Will, above. The S series Raymarine autopilots had a model that was suffixed with a "G" (G2, G3 etc) and Raymarine referred to these as being the "Gyro" version. It was, in fact, a rate stabilising device for the external fluxgate compass. It's primary function was to provide yaw and pitch data to the ACU to make the fluxgate more stable.

The current "heading sensors" marketed by Raymarine, Garmin, Navico etc are a single package device, with provides a stabilised heading to the ACU and other instruments by taking into account roll, pitch, yaw and acceleration.

Have been searching online since you mentioned gyros with Autopilots and I read similar to your post.

As I see - its a "Heading Deflection Sensor with accelerometer" to stabilise the data output ... as a gyro based sensor ... Seymo ... Evolution etc. detects the horizontal deflection ultra fast.
Not really a Gyro Compass .... to split hairs ...

Interesting though.

Lets be honest - no autopilot uses the actual compass reading ie course 170 .... 090 ... etc. What it uses is the CHANGE of heading from whatever is set as desired heading. The compass can be 100 deg in error when start to use AP as long as that error remains throughout use - AP will follow desired direction. Its us really that wants to see compass reading - to reference to the desired charted course etc.

It may surprise some to know that Ships Gyro Compass is not exact and has an error ... its why each OOW is expected to do a compass error at least once per watch and log the result. Usually its only 1 deg or so ... and not usually used in setting course unless greater.
Ships AP is usually a set of sensors mounted under a compass repeater ... older ships had this at helm station repeater, later was to have with a repeater in the nav / command console.

 

[Graham_Wright]

Interesting post ....

Having been a senior Navigating Officer on ships .... one of my responsibilities was to look after the Gyro Compass ..... magnetics as well - but lets stay with the Gyro.
Even the old large Sperry with its sequential shut down / start up routines never took 24hrs to align. I accept it was not instant - but I never had any Gyro take 24hrs .... Anshutz ... Sperry and various others I looked after.

As a Boeing 737 (simulator!) pilot, the spin up time is around 7 minutes I believe.

 

[Mudisox]

I have a fluxgate compass installed in a cabin normally given to guests.
I now, after many problems with "autopilot course" differing greatly to main compass course, tell them not to put anything that might affect the compass in or around that locker. Phones, hairdryers, or even hefty cameras .
I now also always check that the course set for long passages on the autopilot also agrees with my main compass which I have checked once a season. If nothing else a compass swing keeps the mind agile.

 

[William_H]

As a Boeing 737 (simulator!) pilot, the spin up time is around 7 minutes I believe.

I am sure you are talking about the directional gyro. Here the spinning mass has a horizontal axis such that it always wants to retain it's alignment (in space) that it started with. It can be forced (adjusted) to be aligned with north (small aircraft) or as said can be automatically aligned with north. Yes takes time to get the mass typically a disc around 6cms in diameter up to speed in 10s of thousands of RPM. Right up there next to the artificial horizon (gyro) also rigid in space and also turn indicator a rate gyro. But beware my knowledge on these things is 30 years old. Slod state gyros and accelerometers have changed every thing..
Thanks Nigel for setting me right on start up time for gyro compass. ol'will