My understanding is that roofs of church naves in the style of a ship's keel are fairly common: https://www.google.com/search?q=keel+nave+roof+church&tbm=isch h

My understanding is that roofs of church naves in the style of a ship's keel are fairly common: https://www.google.com/search?q=keel+nave+roof+church&tbm=isch https://www.google.com/search?q=keel+nave+roof+church&tbm=is... The metaphor is that the Church is a ship that protects and carries its congregation.