Lee bowing

[dom]

Indeed! Ground wind opens play, modified by tides/currents to produce the true wind, modified by the boat's motion to produce the apparent wind.

The trouble is, one has to pick a constant frame of reference for course calcs, and true wind is the most intuitive. But if tides are a significant dynamic factor, it can be easiest to use ground wind.

The best way to think of the true wind is that experienced by stopped vessel floating freely in the current. It follows that lee-bowing will have a zero influence on the difference between true and apparent wind, for everything takes place on that floating carpet.

The moored buoy on the other hand experiences the ground wind and we must consider its frame of reference to successfully round it. In practice, tidal flows bend, shift, and eddy, which can in turn influence the ground wind, adding an extra complication.

OK -- I certainly agree with all of the above, which is, objectively, correct.

But then why would you torture the term "referenced" to make this point?

We can express wind speed and direction in three ways:

1. Referenced to our boat (apparent wind) (direction typically expressed as degrees from the bow)
2. Referenced to the water ("true wind" in the sense that boat motion is factored out; exact analogue of True Air Speed which has temperature and pressure factored out). (direction typically expressed as degrees from the bow)
OR
3. Referenced to the ground. (direction typically expressed as a compass direction).

......No reason in the world that "true wind" on land needs to be the same as "true wind" as we sailors use it.

Bizarre, it seems like we are saying the same thing! Take a look at the above linked posts from way way back where I tried to introduce the terminology used by the principal electronic OEMs

Upon which I others were lit upon for redefining true wind referenced to anything other than the land :ambivalence:

To which I offered, no problem; one can use whatever inertial frame of reference one wants once they are in a state of constant (rectilinear) motion with respect to each other. This makes for a simple vector translation, but it must be done consistently.

Now you're asking why I'm "torturing the terms referenced". Personally I find it easier to just use the standardised OEM nomenclature as it seems by far the most useful and intuitive

 

[BelleSerene]

There’s an article in this month’s (May 2019) Yachting World on tidal windshifts, by one Mark Chisnell, Technical Coordinator for the British America’s Cup team. I expect he is furious that the magazine has mangled his second vector diagram, ruining his point about how having the tide on the lee bow strengthens and lifts the sailing (apparent) wind.