it is just as those good people say. flatwater speed is all about wind, and a bit of current.
the paddled hull speed of an alpacka is generally null. you can read all about this virtual lack of forward progress from Erin and Hig's website. (ok, yes, they will "move", if paddled with vigor. this is not the same as "speed" or "rate of travel")
"river time" is one of many good things to not include on an excel spreadsheet. it's excessively variable in the short term.
MUCH more predictable is graphing the effects of strolling back into work 6 days late. (if you launch into a weather related diatribe,, "boss ... didn't you grasp that the high pressure system hanging above victoria island would toss down a SE wind and cost us some time ??? how tough is that to figure out ?? ... they will all but invariably suck it up).
HInt : when coming back to work sun-bronzed and stylishly late, for the love of god, do NOT apologize.
if you boss happens to be a woman, say perhaps this : "you have kids : so what is more important in your life ? you children's health, or some form of work ? well ... packrafting trips are a lot like that. so i'm sure we're all on the same page."
if your boss is a man, he should recognize the value of your work, and your ballsy attitude, that he wishes he had. so screw it, it's a good time to ask for that promotion you've had coming, or at least bring it up. : "it's not like I'M the one that's late, you're the one who didn't check the weather. and so what, now you're not going to promote me to plant manger ? we're going to plod along with James, for another year ... another 52 weeks of suffering with his insipid inability to make a decision without checking under your skirt first.. ? come on boss, sheesh ... throw me a bone .... "
so see, either way, screw the river rate factor. take extra food and booze.
if you really really NEED to ramp up the water travel, get up stupid early (2am) and travel in no wind conditions.
and, watch for afterdrop when you get out of a raft after 8 hours or so. it can hammer you to your knees.