Strangely, I cannot find any websites that show how to make caving
harnesses or how to tie prusiks. I learned it all before the internet
but you might try a few caving books. I have done both rock climbing
and caving and caving techniques are closer to what you need to climb
your mast. Rock climbing harnesses are not meant for rope climbing so
I reccomend caving style harnesses. A rock climbing harness is
intended to support you when you fall off the rock while a caving
ahrness is meant to support you WHILE YOU CLIMB THE ROPE. (cavers
rarely climb vertical rocks cuz rocks in caves are so rotten).
For a caving style harness, you want the connection tween seat and
chest harness to be short enough to be uncomfortable when you stand
(Really). This connection is usually made with a short webbing loop
and carabiner. Your chest prusik needs to be as short as possible so
it holds you close to the rope. Your foot loops and prusiks need to
come to mid thigh.
Every time I climbed, I thought "This is really uncomforatble walking
around in and looks like some sort of S&M thing" but as soon as I was
on rope I was amazed at how comfy it was (its a fear thing). As far as
long term comfort goes, I once spent 2.5 hours hanging in my harness
climbing out of a 1000' pit (people above me were slow) and was as
comfortable as you can be hanging 500' above the cave floor.
Never trust your life to a sailboat rope clutch, tie the rope to a
cleat. I don't trust ANY rope that has been out in the weahter for a
few years so I always go up the main halyard while using the jib
halyard as a safety rope also tied to my harness. This safety rope
goes around a winch many times with the person holding the end having
specific instructions to PAY ATTENTION. Always have your partner check
your harness before you climb. Never allow anybody to stand below
while you are up the mast (You will drop stuff).
When you go up, haul your tools up in a bucket below you. You might
want to tie a prusik with a loop to the jib halyard when you are up
there to allow you to step up just a few more inches to see over the
masthead.
Do not allow your partner to lower you. Instead, prusik down. When
you are on rope, NEVER cut a rope. People who get tangled tend to want
to cut things and often manage to cut the rope they are on.
My advice for what its worth.