I liked your analysis, DDW.

In the case of a seaway where swells and waves are (unfortunately) usually from the same direction. I liken it to a double-fall line on a moguled ski slope. There is usually a favored tack from not only a directional stanpoint, but also from comfort, speed, and stability standpoints. Having to adjust to variations in wave face steepness, whether the wave crest is rounded or breaking, the ability to maintain relative controlled speed in both the troughs, up to the crests, and over them -- then down again.

Undertanding the mathematics is useful to getting a feel for what you're really doing to get to a goal. We feel apparent wind; however, if the wind and waves are from where we want to go, then the getting there is not just a question of keep close or lay-off and go for maximum speed.