Surfing Waves

what exactly are "keel" fins?

Named such because they look like a traditional boat keel. Imagine a square shaped fin stuck on a surfboard. Now imagine the leading edge rounded off...that is a keel fin. Hope that makes sense. If not web search traditional fish surfboards with marine plywood fins and have a look. Failing that search Swaylocks site...heaps there.

Around here the term 'keel Fin' refers to any fin which is longer in the base than it is in depth. . .like a 1970's 'fish' fin for example.
It is a bit of a vague term really because keels come in just as many (and more) shapes and sizes as surfboard fins do.