Milton Waddams wrote:
[Default] On Mon, 19 Feb 2007 20:25:04 -0800, "Capt. JG"
wrote:

"Jeff" wrote in message
...
Milton Waddams wrote:
Which is more accurate to use in estimating leeway, the true
wind/current or the apparent wind/current?


Milton
How do you tell the difference between "true current" and "apparent
current"? How do you measure either?

And leeway is a function only of the wind, not of the current.

Traditionally, and by that I mean going back a few hundred years to the
square riggers, leeway guesstimates were based not on wind strength, but
on the amount of sail you had to take in. Bowditch summarizes several
other earlier writers and claims:
"1st. When a ship is Close-Hauled, with all her sails set, the water
smooth, and a moderate gale of wind, she is then supposed to make
little or no lee-way.
2d. Allow 1 point, when the top-gallant sails are taken in.
3d. Allow 2 points, when the top-sails must be close-reefed."

Nowadays, if you did it at all it would be based on the tables generated
by a "Velocity Prediction Program," the same software that generates polar
diagrams. These tables are usually organized by true wind.

Maybe he's thinking of set and drift...


Can you explain set and drift? Thank you.

As mentioned, set is the direction the current is flowing, and drift
is the strength. It is important to remember that current does not
have a noticeable affect on the boat unless you can take bearings, or
use the GPS to determine that your motion is not what you might first
imagine. Sometimes people make silly claims, like you can feel the
current on the rudder, but assuming there is constant flow in open
water, its best to think of the current as a shift in your coordinate
system. When plotting, you use vector addition to add in the affect
of the current.

Leeway is quite different, since it is a function of the way the
particular boat responds to the wind. It is usually minimal except
when going upwind. When plotting, you add in several degrees (as
appropriate) to your angle to the wind.



Milton

BTW thanks to everyone for their generous help on all my questions.