RogueIT wrote:
So I can tie a bowline and a figure 8 but I am not sure what their
primary
uses are on a boat.

1. can anyone tell me what they are used for?
2. what other knots should I know and why are these knots used?

As others have stated, a figure 8 is a stopper knot, it keeps a line
from accidently running through a fitting. A bowline is a fixed size
loop at the end of a line that has many uses.

Note that strictly speaking a "knot" is a line tied to itself. A "bend"
is a line tied to another line. A "hitch" is a line tied to an object.

You should learn at least one good bend and one good hitch. "two half
hitches" is a very good hitch. When a cleat is available, use the cleat
hitch. There are many others hitches, but these two will suffice for
most purposes.

Probably the most common and easiest bend to learn is the sheet bend
(not the sheep bend, as someone called it). Do NOT ever use a square
knot (or reef knot for the Brits) to tie two lines together if it's at
all important that they stay tied. It's called a "knot" rather than a
"bend" for a reason - it's great for it's intended purpose (reefing
sails) but useless or dangerous as a bend.

The bowline makes for a passable hitch, although the loop can catch
things it's not supposed to which makes it unsuitable for some
situations. The bowline also makes a passable bend by tieing the loop
of one around the other. Again, you have two loops that can catch
things, making it less than ideal, but it's definitely better than a
square knot for tieing two lines together. The bowline has many uses,
which is I guess why it doesn't get the qualifier knot-bend-hitch.

So a good set of basics for the sailor's toolkit is:

Figure 8 for a stopper knot
Two half hitches to tie lines to objects
Cleat hitch to tie a line to a horn cleat
Sheet bend to tie two lines together.
Reef knot to reef sails.
Bowline for multi purposes

Those six will go a long way. You'll pick up other specialty knots
along the way, but learn these six first.

//Walt