Harry,

quote "Now the Upwind boat must keep clear of the downwind boat, simple." Not so simple, The windward boat shall keep clear, meaning the downwind boat (the windward boat) on the same tack must keep clear of the boat sailing upwind.

There is no distance given as conditions and speed will influence any decision you make. If the right of way boat alters course to avoid a collision which he must do, the other boat will have trouble convincing a protest committee that avoiding action was not required.

Hope this helps

Mark