Centerboard or Daggerboard
Centerboards and daggerboards are raised and lowered by the crew either manually or mechanically and when lowered they provide the same funtions/benefits to that of a keel on larger boats. They are most common in sailing dinghies. The daggerboard is attached to the boat by a pivoting mechanism allowing it to be raised and lowered as required. When retracted it resides in a housing in the centre of the dingy
When raised, they reduce both draft and wetted surface. When lowered, they provide many of the same benefits as a keel, though in smaller boats they are often unballasted. The ballast being provided by the weight of the crew; often referred to as live ballast. Centerboards or daggerboards are common on sailing dinghies, as well as on high-performance catamarans and trimarans.