Last month, I looked at two boats going downwind towards the leeward mark and the requirement to look to leeward for boats coming upwind. This month I want to talk about looking astern. I have commonly heard reference to a rule, “overtaking boats must keep clear.” This rule is actually not in the rulebook (though something close is in Colregs, governing boats not racing, but that’s outside the scope of this article). It is a good shortcut to remember rule 12, but there are some important differences.