I hear the terms all the time and have a general idea. I am laid off and bored at the moment and thought I would post. Please explain what and how maybe some examples or whatnot about how to take advantage of them. Thanks for any replies.
A header (or 'knock') is a wind shift that tends to head your boat more downwind (or away from the mark, if sailing upwind to a mark)
A lift is a wind shift that tends to head your boat more upwind (or toward the mark, if sailing upwind to a mark)
Generally, lifts are your friends and you just ride them. Sometimes you can get lifted all the way to a mark and not even have to tack (you're 'golden.')
Generally, headers are not friendly to you and if there is a general tendency to be headed on one tack, it's time to tack over, because a knock (header) on one heading/tack will be a lift on the other
Of course the converse is true if sailing down to the low/downwind mark.
Watch for trends, and try to act on them. Time On the Boat (TOB) give you experience to judge shifts, so just be patient
Multihull girl is right. Lifts lift you towards your destination when beating upwind but may be less welcome downwind since it could turn a broad reach (usually faster) into a dead run (slower). Headers opposite.
Another thing is what kind of wind/weather is it? If it's a "persistent" shift in one direction, then you want to get there first and be to windward of the competition and stay there so you sail less distance than they. Lifts help the windward boat and hurt the leeward boat. And again, headers opposite.
But if it's an oscillating wind, back and forth every few minutes (more common after a cold front passes, at least where I grew up), then just figure out the "average" wind by taking a few shots into the wind and watch your compass, or go close-hauled on both tacks and watch your compass. That way you'll know if you're heading worse than "average" at any given moment, or better. If better, stay on til you get headed, then tack. If worse, tack away and it will (should) be better than average on the new tack.
"Tack on headers--stay on lifts" is good "vanilla" advice. "Pistachio fudge ripple" exceptions to this, in particular situations (usually at the beginning or end of a beat) can be learned as you go along.
It's why racing, especially upwind, is seldom dull.
I'm thinking of when you have to ride a header, or tack off of a lift, say to clear your air at the start, or to avoid overstanding near the lay line. And something about getting back "in phase"-- ow, my head hurts now...