You were told wrong. The "navigable water" part applies only at the start. See the preamble to Part 2, Section C.
The anchored yacht and dinghy you describe were an obstruction. Since the leeward boat chose to sail below them, he was obligated to give you (as inside boat) room to avoid it.
Regards,
Eric
US Sailing Certified Judge,
Member Area D Appeals Committee
Eric,
Just to clarify this in my own mind.
In a mark rounding you have to provide room for the overlaped boat to execute a rounding. You do not have to provide them room to do a rounding where they go wide/sail where they wish.
Given this why if in Robi's case, assuming that there was plenty of time to avoid the obsticle to either side, would the leward boat be obligated to allow them to decide how they were to pass it. I see where they could not come up to force closure at the last minute.
Thanks
Matt