How long does a dry fly need to float?

[JohnScott]

...How long, on average, does a fly need to float before the next cast (at which time the cast will again "dry" the fly)?

I know, when you are fishing to a rising fish, it seems like forever that you need the fly to float into the trout's window. But, I would guess that it is less than 10 seconds in most cases!!!

What do you think?...

... if you do the math, given a 3 mph* current speed, 10 seconds would result in an approximate 44 foot drift and given a 4 mph** current speed, 10 seconds would result in an approximate 58 foot drift.

That would suggest that your guess above is a good one, at least for the vast majority of fly anglers in the vast majority of situations.

John

*3 mph = 5280' x 3 = 15840' / ( 60 seconds x 60 minutes = 3600 ) = 4.4 fps x 10 seconds = 44'

**4 mph = 5280' x 4 = 21120' / ( 60 seconds x 60 minutes = 3600 ) = 5.8 fps x 10 seconds = 58'