Complex sentence: The 420 (dinghy), Vanguard 15 or Flying Junior are the dinghies most frequently used for team racing while the Sonar (keelboat) or Ideal 18 are the keelboats most frequently seen on the team racing course.
Split into simpler sentences: The 420 (dinghy), Vanguard 15 or Flying Junior are the dinghies most frequently used for team racing. While the Sonar (keelboat) or Ideal 18 are the keelboats most frequently seen on the team racing course.