Bill Gladstone, the author of the North U series of racing books, has a posting on US Sailing site on when to split tacks with the leaders when you are behind.
You know the old adage: “Can’t catch ‘em if we follow ‘em.” So, when you are behind you’ve got to split tacks to catch the leaders. In fact, splitting tacks is often a gamble with poor odds of success. To understand why, first answer this question: Which way are the leaders going, the right way or the wrong way? (Hint: they are in the lead.) If they are going the right way then splitting to go the wrong way is a low percentage play.
What to do instead:
First off, recognize that if the leaders don’t make any mistakes, you won’t catch them.
Don’t just split tacks for the sake of splitting. You’ve got to sail fast, and stay within striking distance so you can pass when they stumble. When the leaders are going the right way, then go that way. If they become preoccupied tactically and miss a shift, or fail to respond to a change in conditions (either tactically or in trim) then you get your chance.
But if you split for the sake of splitting and go the wrong way, then you will likely fall further behind; and you won’t be in position to capitalize when the leaders make a mistake.
Sail fast, be patient, and pounce when the opportunity arises.