Originally Posted by erikdj
Those of us who sail in the San Francisco Bay often see 20-30kts every summer day. It's been my experience that if you don't ease the main immediately after jibing, the boat will round-up (broach). If one thinks about the boom as a giant lever arm connected to the boat's z-axis (parallel to the mast) and the wind is the force at the center of effort (the sail), then keeping the main in enables the strong wind to spin the boat quickly.
I think the question that both NCC and I had was why the moment arm is any different right _before_ the gybe, when the boom is still on the old side. You've got the exact same forces trying to make you round up in the _other_ direction, right?
From the responses so far, I gather the difference is that right after the gybe, you've got some instability from shock loading on the boom and rudder. I suspect it may also be because you were already steering into the gybe, which works against a pre-gybe round-up, but in favor of a post-gybe round-up.