"Jeff" wrote
Bart - it really sounds like you have the same misunderstanding of current
generated wind that Ellen did.

When you have zero true wind, but a strong current, there will be an
apparent wind that is indistinguishable from a real wind if you are not in
a position to detect the current. For example, it you are in the middle
of the ocean with no wind but a 10 knot current, that will feel exactly
like a 10 knot breeze. There would not be any weird affect like the
rudder having "no bite" and "losing control."

Not true Jeff. Think about it. Consider Case 1 and 3 below. Think
about a powerboat going down-river. A slow moving boat, say
just slightly faster than the current will have minimal control over
his steering. A boat drifting will have no steering. While a boat
moving much faster than the current will have good helm control.
Rudders don't work without water flowing by them. They work
by deflected the flow, not typically by sculling

As for going faster than the current - if the boat can go faster than the
wind, which some do, then you can go faster than the current. But not
directly up or down current.

Agreed. But it would take an extremely fast boat--a typical boat would
not be able to do this. It is clear you could only hope to accomplish this
sailing across the wind. As I stated, you would still be better off sailing
into the current which would reduce your speed and give you more
control--in the typical currents you are likely to encounter.

Bart wrote:
Gilligan wrote:
On a windless day, is it possible to drift with the current and use that
relative wind to power the boat faster than the current?

If so, could you go over why it is possible. I could never figure that
one
out.

I don't think so, even though you could increase the
apparent wind at the expense of control.

Case 1: In the direction of the current:
You would be shoved along at the same rate and
your sails would hang limp. You would be "In Irons"

Case 2: Against the current:
The wind made by the current would push you slower
than the current, and you would still be forced in the
direction of the current. You would have no control
of your steering and at the mercy of the current.
Your speed would be the speed of the current less
any aerodynamic drag.

Case 3: Across the wind (90 degrees to the current):
You would be pushed at about a 45 deg angle "with
the current" and you would have to trim for a close haul. If
you tried to head up at all you would stall the boat
and go "In Irons" as in Case 1.
.
Your Boat Wind would be less than the Current Wind,
however, combine the two and the Apparent Wind would
be slightly greater than the Boat Wind. Could the boat
then sail faster than the Boat Wind or Current Speed?
I think in a light boat in might be possible. But the
difference if any would be negligable. In most boats
your speed would be less because of drag.

Clearly, this direction would give you your best boat speed,
but since you are now moving in roughly the same direction
as the current your helm response would be horrible. Who
would want less control in avoiding obstacles "down current"?

Case 4: 45 degrees into the current:
This should give you roughly beam reach sail trim, and
the boat would be moving slightly in the direction of the
current. In this case the vectors cancel somewhat and
your Apparent Wind would be less than the Current Wind.
You would be able to avoid obstacles and steer better as you
would have good flow across your rudder. This would get you
away from a dock--in slow motion, and away from danger with
the most control. Your boat would still be moving down current
while making the best possible speed away from a dock or shore.