Aldo re: “offset”

In this case, “to offset” is being used as a verb, not an adjective. 

I think “to offset” comes from accounting … it’s a verb that describes something on one side that balances something on the other side so that the result is zero/neutral. $200 of income “offsets” $200 of expenses. 

You can also imagine balancing a scale.  One item on the left side will “offset” the weight on the right side to balance the scale. 

When you “offset” one thing with another, the result is zero, ‘in the middle’ or ‘back where things started’. 

Common synonyms for “to offset” in this situation could be “to counteract”, “to negate”, “to neutralize”. 

I think the concept is you can scull to facilitate steerage only (boat stopped. in irons) but not in cases where you are using to as propulsion, and this is a new case where you are using sculling to sneak a boat to windward, "crabbing" Backing the sail, board up you can crab pretty well, now add in aggressively sculling to windward it gives you even more of an advantage and is not done to facilitate steering. The wording could be clearer though.   

I remember on the water judging at an optimist event a few years ago. Two things that stick in my mind, an oppy could be on the second row, in the worst dirty wind, and suddenly zip into a gap on the first row. Secondly, there was lots of sculling on the starting line, but as soon as a helm pushed the sail back whilst sculling it was recorded.

Charles, re: “helm pushed the sail back whilst sculling”

That brings up an interesting question … what if the back-winding and sculling are done close in sequence but not simultaneously?

Seems the way it is worded, that would be prohibited as well as long as the umpire could associate the 2 actions.  Thoughts?

I expect with two separate actions the sculling would still be to offset the steering effect of backing the sail. 

Angelo, thanks for the offset, that's clear. Now, what's the offset "steering" ? Can you make me an example ? 
I imagine (and i might be wrong) this: backing the sail, rudder on a side, by going astern the boat steers, and the sculling is to prevent the steering ? 

Aldo … yes .. close to your example. 

Assume we have an Opti. 

PS: .. and yes, the net result above would likely be a boat crabbing to starboard.  

Ang, for me, that's just momentum, and there is no 'steering' after the main is not backed.

So I look to see the two actions (backing main and forceful rudder movements) occurring simultaneously.

Spotting a backed main is quite easy.  Hand on boom (or even sneaky shoulder or even head) and sail filled; stands out.  Then just watch for forceful rudder movements.

Ben, about your """ what if the back-winding and sculling are done close in sequence but not simultaneously? "", my view is that, 
- sculling simultaneously, boat breaks 42.2 d) (... or  prevents her from moving astern )
- sculling after backing the sail, again 42.2 d) ( ... that propels the boat forward)
Plus, any "forcefully action" either propoulsive, or not.

My first question originates from a Coach comment i got few weeks ago; he was saying that backing the sail and sculling to avoid the boat changing direction, was not breaking RRS 42, ""according to new Worldsailing interpretation"" (verbatim).
I red (again) the translated interpretation of Worldsailing, found "SCULL 3" that says "to avoid going astern";  no mention to steering. 
Maybe the Coach was right? I miss some updatings?
Then i checked the original Worldsailing text, and found that " offset steering of the boat ", that's sound quite different from the translated version.
That's why i asked help in understanding the english first, then a description of the situation. And thanks to you all for that.
I have no doubt, now,  that the infraction is there; sculling either forcefully, or to avoid steering, or to avoid going astern = yellow

I would remind you that a sail can be backed by oversheeting - pulling it to windward so far that it fills on the opposite side. That is permitted, but sculling to prevent the boat turning while the sail is backed is not.

https://www.youtube.com/watch?v=AC4nUytWWbQ

https://www.youtube.com/watch?v=2vtNHroAaGA