Raymarine EV-1 "yaw" definition

[ironman]

The Raymarine EV-1 transmits PGN 127257 Attitude, which includes a field called 'yaw'. This seems to coincide somewhat with 127250 Vessel Heading, but not quite: there seems to be some difference. Question: what is that difference?

[nuku34]

"yaw" is the tendency of a vessel to "wander" back and forth around the intended vessel heading. For example, say you specify 0 degrees as the course you want the autopilot to steer, then depending on sea state, the actual heading at a given moment might be anywhere between 365 to 10.

Yaw, pitch, and roll are all words that describe how a vessel moves in the water. Yaw is a turning movement (change of heading), pitch is the bow going up and down, roll is side to side rolling of the boat.

Your autopilot is tracking all of these movements since they all affect the rudder adjustments it is making to keep you on your chosen course.

[ironman]

Ok so you say that in the EV1, yaw is defined as 'heading error'. Then it would indeed make sense; assuming the default 'heading to steer' would be 0, that it follows the HDG. I forgot to mention that the yaw values range between -180 and +180, which would be consistent with your explanation. Thx!

[Brian.D]

+/- 180° is rather extreme for 'yaw'. It should be more or less +/- 20°. If your vessel wanders off by 180° then you are basically heading back to where you came from. That seems silly. JMHO

Is it possible that this is an alarm setting to let you know if you wander to far off course?

[ironman]

I guess it also transmits these messages when the autopilot is off; then it can be expected to see these extreme yaw values.

[deblen]

Each vessel has it's own tendency to yaw.
To find your vessels yaw, take her out,under power and on a substantial following sea.
Hold the steering dead center-do not move it-& watch the compass for a bit.
Note how many degrees to P & S of your desired course that your vessel wanders. That is yaw.
Perform same test with quartering seas. Yaw should be less,but still there.


Finally,perform same tests under sail.


Now you know your vessel's natural yaw in different sea directions. Of course,yaw will generally get worse with worsening sea conditions.


An autopilot should not be expected to steer much better than your natural yaw. Yes,you have a yaw control & you can set it to hold a tighter course & it will.
But-the pilot steering mechanics(ram,rudder,etc) can beat themselves to death,if you ask too much. This can also burn a lot of amp/hrs.
Be reasonable.
Cheers/Len

[Tehani]

It happens that the Euler angles (Yaw, Pitch and Roll) are expressed in degrees from -180 to +180 (-PI to +PI radians), while the Heading is expressed from 0 to 360. That is, a Yaw of - 90 equals a Heading of 270.

It also happens that a "fine" Heading can be the projection of the Euler angle "yaw" on the terrestrial horizontal plane. But this is not very important with a normal heel.
This change of plane is a function of the other two angles: Pitch and Roll, so if Pitch = 0 and Roll = 0, then Heading = Yaw (with +360 correction for negative values).

Heading's variation speed is given by another data: Rate of turn (PGN 127251).