a tether has about 1.5m. It cannot be smaller. If the boat is not big, when you go forward and are walking on the side, it will be enough for you to go overboard. You will not go far but you will stay in a position where I don't know if it is possible to get back to the boat, a dangerous position that can led to drowning.
When you use a tether and go forward you should have one hand for the boat an another for the tether, pulling it all the time to make it tight, without slack. that will permit you to have a very solid hold. when you reach the place where you are going to work, than you are not moving and can hook the theater in a place where you cannot go overboard (on the center of the boat). at least it is what I do