Page 58 - Mario Bigon "The Morrow Guide to Knots"

3
SLIPPED
HALF HITCH

This is a variation on the
simple half hitch. Because it is
slipped it is easier to cast off,
particularly when the rope is
under strain, since pulling the
end automatically releases the
knot (4). Sailors use the
slipped half hitch for head
and reef earings.