True Wind - your definition.

[lw395]

The red boat is sailing beyond the layline.
It will have to ease sails and reach to the mark.
The mark is a moving target, the layline when you get there is the one that matters.

When fixed objects like marks are involved, I tend to think in a geostationary frame, the tide is moving not the mark.

 

[Yealm]

And I expect most of the 66% majority also refer often and casually to the number on the instrument labelled true wind as true wind. Despite claiming on this post topic that this is not true wind (and that true wind is actually the term for ground wind).

Whatever your preferred terminology, you do need to have 3 words to distinguish 3 different wind types (which all the manufacturers call ground, true and apparent wind).

And to the many posts that suggest all this is pedagogical rubbish and you can just put your wetted finger in the air or look at the wavelets - I'm surprised. For me, sailing is an amazing existential pleasure, but the geeky side - understanding the physics and forces acting on the boat - is also fascinating.

Now I support everyone's right to use language exactly how they want to and I suspect that many in the ybw demographic are uncomfortable with the notion that "truth" may be subjective rather than absolute and universal. However, the question was about what you mean when you use the term, not what you think in your head it would best be applied to.

The only time I think I use the term "true wind" on a boat in a non-pedagogical context is when asking about or relating the numbers on the wind speed indicator. It would be a perverse skipper indeed who, when asking a crewmember for the "true wind speed" expected an estimated current correction to be applied to the numbers on the instrument before being relayed.

 

[DJE]

All you have done is rotated the frame of reference so that the sailing wind is blowing down the page. This doesn't make it a moving frame of reference. It is still stationary. If you want to use a moving frame of reference then both the start line and the windward mark will be moving.

 

[BelleSerene]

All you have done is rotated the frame of reference so that the sailing wind is blowing down the page. This doesn't make it a moving frame of reference. It is still stationary. If you want to use a moving frame of reference then both the start line and the windward mark will be moving.

Yes, you're right. I could (should) have omitted the start line from my diagram (or else marked that it drifts uptide just as the windward mark does). All that matters in the water frame of reference is the boats' start location on the water, which I showed.

I am not sure what you mean by a moving frame of reference; the point of a frame of reference is to examine how things move relative to it. In this case, what's moving (as well as the boats!) is simply the windward mark. (It is also true, if irrelevant to who wins the race, that the start line, being fixed to the ground, is drifting uptide in the same way.)

As lw395 is saying in #161, the red boat, seeing only the layline to the current position of the windward mark, is moving above its (eventual) layline, and so he's extending his course. As I believe we both accept (lw395, please feel free to disagree with me), the moment Red oversteps this eventual layline, he is going to have to sail further to the mark than Green, even though the two boats are equally far upwind.