Complex sentence: Unlike broaches with other types of sails, a broach with a spinnaker is actually more likely when trying to reach than when trying to run, so bearing off the wind is the correct response to signs of an impending broach.
Split into simpler sentences: Unlike broaches without spinnaker, a broach with a spinnaker is actually more likely when reaching than when running. Bearing off the wind is the correct response to signs of an impending broach.