Keel

[reece1]

Why should you have a keel on a sea-going ship?

[Blender]

The other reason especially if it's a sailing ship is that it keeps it sailing in a straight line rather than crabbing

[BenDToy]

This is question number 1 on the same web page as all your other questions. http://familygames.com/features/quizzes/qze/q1.htm
l With appropriate acknowledgement to Obo for this.