Friday, 13 April 2012

Relative Velocity (Delta Vector the Game)

I could do this SOOOO much easier if I only had used hexes.  I know a simple equation that would work for all situations and be much faster.... but nonetheless...

If ships are stationary or approach side on, use the velocity of the fastest ship only.

If ships are closing, subtract the lowest velocity from the highest.
Note this rule could change if I enforce a "hard upper limit" of 20" velocity

If ships are heading for each other at less than a 45-60d angle or so, they are closing.
Add both velocities together!

Vector paths can cross in front or behind a ship - it is the angle that matters, not where the paths intersected.  This is a perfect example of a side on attack, as the angle is near 90 degrees. It is NOT a rear attack.

I really think I might switch to hexes as I could have used a single photo and forumla to show all of this. If you can think of a better way to do it (hexlessly) please let me know.

EDIT: Here is the hex rules with a photo illustration
The dark blue line shows the blue ship's actual movement path. The light blue line and marker show the imaginary line and path the blues ship would have if it shared a starting point with the greenship.

The red dotted lines show how many hexes between the imaginary drift marker of blueship with the actual endpoint of greenship. The difference is 11 - giving a relative velocity of 11...


  1. "I could do this SOOOO much easier if I only had used hexes. I know a simple equation that would work for all situations and be much faster.... but nonetheless..."

    I'd be interested to hear/read your hex version ..

    1. I don't have a camera (or hexmap) handy, but basically this:

      Pretend both ships are moving from the same initial position (i.e. pretend ship A is starting from ship B's hex)

      Layout a pretend drift marker from ship A at the actual angle and distance from the real ship A's drift marker is.

      Now measure from ship A's pretend drift marker to ship B's actual drift marker.

      Ugh my head hurts re-reading what I wrote. I'll get the camera sometime. If you understood that, then I'll teach you the secret handshake... :-)

  2. And then you simply just count the number of hexes between the drift markers ??

  3. Yes, I think you have it.

    To re-explain. If you looked in the last photo, and moved the blue ship base to be in the same spot as the green ship base, but had the blue ship drift marker pointing at the same angle and distance from the blue ship base as it did in its original location, THEN measured the range between the pretend blue drift marker and the green drift marker, you would have the relative velocity.

    This could easily be eyeballed with hexes (as ranges are clearly marked and straight lines and angles clearly dilineated)

  4. I think SFB chose which moves first and uses its intended positions for deciding facing.

  5. Oops; after reading this blog post again I realize you are ALSO trying to determine the magnitude difference between velocities of two ships; ship A and ship B.

    Take the offset of ship B and apply it to ship A. And then measure from between ship B offset and the revised ship A offset. That is the vector difference. The length gives you the magnitude (difference in speed).


    1. These rules have gone through a LOT of iterations since then; perhaps a more recent version is in the google group?

      It's not precise; I think I ended up with head v head = add speeds; everything else = use the fastest speed (I think I was using a Lost Fleet "hard" lightspeed limit of 20-anything)