I honestly don't know. I know that this is argued in the Seaplane's
pilot association newsletter ad nauseum. One thing to further
complicate things is with a Seaplane, water speed DOES matter. Faster
water speed gets you on the step quicker and that means shorter takeoff
runs. Also, TOO fast a water speed (on landing) can cause a bad
accident (this would be landing upstream with a tailwind). People who
takeoff on fast moving rivers do report shorter runs (relative to the
ground) going upstream. What is debated is whether they are getting
shorter runs relative to the water, than a downstream run with the same
headwind. But like I say, I dunno. The real world scenario is NOT
trivial. My bottom line is I need to have plenty of room to take off,
so I never really pushed the issue. I always wanted 2 or 3 times as
much distance as I needed. If I didn't have it, I found a longer lake
or river. Rivers tend to be plenty long, at least the ones I've dealt
with. My experience with rivers is limited to one or two and they were
fairly easy, plenty long. I always just took off into the wind.

Gary Drescher wrote:
"Doug" wrote in message
ps.com...
Actually, on a moving river, water speed matters and frequently speed
(well, distance really) relative to the ground matters.
....local obstructions dictate
you concern yourself with distance of run relative to the land....

Sure. That's why I said that *if* the river is arbitrarily long, and if you
don't care where you land, *then* you just ignore the land and care only
about the speed of the air relative to the water. (Those stipulations make
the situation analogous to the hypothetical conveyor belt scenario.)

The ideal setup
is to have a headwind while pointing downstream. That way you have
slowest waterspeed and shortest run.

The plane's speed relative to the water (the plane's waterspeed) depends
only on the plane's airspeed and the speed of the air relative to the water.
It doesn't depend in any way on the speed of the water relative to the land;
hence, it doesn't depend on whether you're going upstream or downstream.
Rather, it just depends on whether you're going upwind (relative to the
water) or downwind.

As for making the shortest run (relative to the land), wouldn't you want to
be going upwind (relative to the water) and upstream, rather than upwind and
downstream?

--Gary