Hi Stephen ... thanks for the input & I agree with you, with a caveat. I appreciate this discussion - I hadn't really thought a lot about it previously.
Not that it means I should have any credibility but I’m also an engineer (Civil PE), an ASA sailing instructor, and a Coast Guard Masters license holder. We have all seen people with those papers be
wrong, however, I did sleep at a Holiday Inn Express last night
.
This whole discussion started because I said a feathering prop would make a big difference especially in light winds & with opposing current. Bert said current has no effect on drag.
I’ve been flailing around trying to describe why I thought current
did make a difference. Not thinking about the physics of it, when we are racing & keeping up with the pack, we round the downstream mark, head upstream & all the other boats (with feathering or folding props) pull right away from us.
It's very noticable and it is at the point in the race where we turn upstream.
I agree with Bert, Chris and you that the amount of drag is generally the same with or without the current. However this is in a
steady state condition (after acceleration). I've been trying to think of why there is a noticable difference when we are racing in the current. I've settled on the difference being because of the
acceleration.
If we were racing in still water, we would get the boat up to speed, cross the starting line and it would generally stay up to speed with smaller reductions for tacking, rounding marks, etc. When there is a strong current, I think there is more acceleration and deceleration.
When we round the downstream mark and head upstream we are going from a water speed of 3 knots downstream to essentially a stop, then accelerating to 3 knots in the opposite direction. Because of the added drag, we accelerate more slowly and that's why the other boats pull away.
At least that's my current theory. No pun intended.
Opposing theories are welcome.
Cheers,
-Mark