Tactics Plugin

[NAV]

For my own understanding, I made a drawing using the standard navigational expressions (so I didn't use the terms that are common in yacht racing). This drawing is for upwind situation, not for the waypoint situation.


If anybody thinks there is an error in this drawing, please let me know.

[tom_BigSpeedy]

NAV,

forget about the term CMG as long as you don't use an active waypoint.
CMG is only used in conjunction with waypoints.
I redrew your picture, using your colours ...

See my changes in orange colour please-



I can draw another one with CMG, as soon as this one is clear...


Thomas

[NAV]

Originally Posted by tom_BigSpeedy

NAV,

forget about the term CMG as long as you don't use an active waypoint.
CMG is only used in conjunction with waypoints.
I redrew your picture, using your colours ...

See my changes in orange colour please-

Attachment 140332

I can draw another one with CMG, as soon as this one is clear...


Thomas

Thomas,

I see that I did understand things correctly. In my drawing I didn't want to use the terms VMG and CMG in the way that is common in yacht racing.

I will add the velocity component into the wind for the actual heading and STW and repost this together with the drawing I made for the waypoint situation.

I only do this to be sure that I understand correctly what information you are presenting in the plugin. I'm not used to yacht racing, but have sufficient knowledge of both sea and air navigation.

[NAV]

Attached are my 2 drawings indicating the "upwind" and "towards waypoint" situation. Again sticking to the navigational terms for CMG and VMG as e.g. used in Bowditch, so on purpose not using the sailing terms.

[fgd3]

In your drawings you show two positions with a line between them. That line shows your actual course. Actual speed through the water should be measured along that line, not along the heading line.

Fabbian

[NAV]

Originally Posted by fgd3

In your drawings you show two positions with a line between them. That line shows your actual course. Actual speed through the water should be measured along that line, not along the heading line.

Fabbian

Fabbian,

The black line between the 2 positions shows the Track Made Good (with Course Made Good and Speed of Advance), which is history and not actual. If the situation does not change (all variables including current and wind remain exactly the same) the angle between the black line beyond position 2 and the North direction indicate the actual COG. Speed measured along that line is SOG, not STW in my opinion.

[fgd3]

You're right.

Fabbian

[NAV]

Again the two drawings now with TWA added and with one correction: I changed SOA to SMG.

[rgleason]

NAV nice diagrams. I see you are using CMG & SMG for both conditions, VMG to upwind and VMG to waypoint.
I guess that is ok, but I thought we were trying to make a distinction between the terminology vmg to wpt & to wind.
I'm interested in what Thomas says about this.

[NAV]

Originally Posted by rgleason

NAV nice diagrams. I see you are using CMG & SMG for both conditions, VMG to upwind and VMG to waypoint.
I guess that is ok, but I thought we were trying to make a distinction between the terminology vmg to wpt & to wind.
I'm interested in what Thomas says about this.

Rick,
For my own understanding of the plugin, I have just tried to stick to the official definitions of CMG and SMG as given e.g. in Bowditch (the course and speed made good between the positions t1 and t2). The actual velocity components upwind and towards waypoint are not described in Bowditch, so I've tried to show these as just that: velocity components of the vector HDG & STW (being V_upwind and V_towards wpt), and I haven't given these any special name as is common in the yacht racing world (VMG and CMG as used by NKE are misnomers in my opinion).


In fact, Bowditch describes Course Made Good as a misnomer too, and prefers the use of the term Track Made Good.

The additional problem we have in the Netherlands: the words for velocity (vector) and speed (scalar) are the same ("snelheid").

[RogerD]

OpenCPN already defines VMG - "VMG Velocity made good to next waypoint" in the "Active Route Console Window".
In my opinion, if that definition is not going to be used in the Tactics Plug-in then it must also be changed in the main program, We don't need two different definitions for the same parameter (VMG) that could be shown in two different places on the same scream (tactics display with an active route).

I agree that your diagrams are excellent. Nice work!

Roger

[rgleason]

https://opencpn.org/wiki/dokuwiki/do...al:terminology

Roger D and Nav we have had some lengthy discussions and tried to resolve terminology. At this point I'm not so sure its worth starting it up again as there are so many different ways to look at it!

[rgleason]

I just happened to be checking the Tactics_pi documentation and noticed the terminology used there:

CMG Course Made Good; the speed approaching a waypoint

VMC Velocity Made on Course; same as CMG

VMG Velocity Made Good; the speed up-downwind with
reference to true wind direction

So I guess we are consistent about terminology within a given plugin. I was not able to get others (primarily powerboaters) to buy into our sailing definition of VMG, so we have just left things the way they are, and made our own definitions for the plugin.
https://opencpn.org/wiki/dokuwiki/do..._tools:tactics

I think this is a good point.
VMG velocity made good a vector made up of an angle and distance
CMG Course made good an angle
SMG Speed made good scalar, a distance or speed.

[NAV]

For definitions related to direction and speed as given in Bowditch 2002, see attachment.

[NAV]

And again, now with a correction for the terms leeway angle and drift (for the Dutch situation and definitions only).