Sometimes people can get overwhelmed by the knots they feel they need to know for sailing.  But essentially, you need to know just a few. 

• How to do a cleat hitch*
• How to tie a half hitch
• How to tie a bowline
• How to tie an alpine butterfly

* it’s good to know when to use half wrap, full wrap and multi-wrap cleat hitch, but not essential.

Here are some great youtube videos from great sailors willing to share their knowledge of knots.  Beware, there are many sailing teachers who feel there is only their way to do anything.  There are always more than one way to do things, and sometimes other ways are better, sometimes worse. Don’t get too fixated.