The “Late Main Gybe” method is the key to the fastest possible asymmetrical spinnaker gybe. Delaying the boom’s crossing avoids the main blanketing the spinnaker as it is trying to re-fill.
In a Late Main Gybe, the helmsperson needs to stop the boat’s turn just beyond dead downwind. At this point the spinnaker is almost completely on the new leeward side and the boom is being held out to the old leeward side. The boat will be wing-on-wing for second before the turn is completed. If the boom comes across too soon, the boat will have to head up too much in order to get wind in front of the main for the spinnaker to fill, which adds extra distance and more time with the chute not pulling.
To sum up, do not to turn too fast and assign someone to hold the boom until the chute fills. If it is too breezy to hold the boom safely, make sure the boom stays centered until the chute re-fills.
The mainsheet trimmer needs to say loudly, “Boom’s coming across!” when it is released to warn the crew to duck out of the way. It’s best to have an extra person holding the boom so that the main trimmer can pull in the slack in the mainsheet to keep the loop of loose sheet from smacking a person or catching the binnacle.