Re: Essential knots?
Definetly the bowline is an essential knot. Though the halyard knot is what I choose for tying shackles to halyards. They are stronger but after being loaded they are nearly impossible to untie.
The rolling hitch is something that I use every day for various purposes. It's probably my favorite. If you go aloft on a halyard and then discover that you need to work on the sheave that you're using, you can tie your self off to a shroud or even to the mast. Thereby freeing the line. I've actually used rolling hitches tied around the mast itself to get to the top of fractional rigs. The rolling hitch holds when loaded and can be slid when unloaded so it's great for things that you need to adjust. If you get an over ride on a winch, a rolling hitch can be tied around the standing part to take the load.
The sheet bend is great for bending two lines together and is constructed exactly like a bowline.
The clove hitch is very handy.
I use a trucker's hitch a lot too.
And of course, a plain old figure eight is a handy stopper knot.