re: safety line
You attach a rope that runs from eye of your bow cleat (the one you use to pull your boat out of the water) to the stern of your boat (there's a cleat on either side of my transom, but I suppose you could also use a cleat attached to the gunnel at the stern if it's strong enough). You then have a rope that attaches the safetly line to the scotchman, and you attach the rope to the safetly line using some sort of qiuck release eye for at least two reasons. Firstly, the eye on the rope attached to the safety line will allow the rope to slide back and forth on the safetly line, so once all your gear is in the water, the rope to the scotchman slides up the safety line to the bow as the boat pushes against a current. That's what you want, the bow facing against the current. If the stern faces the current you may swamp your boat as the water tries to push over the transom while the anchor tries to force you down against the current. Secondly, if you get in any sort of trouble (waves or current or both), you need only to cut (or release) the safety line and your boat is no longer attached to the scotchman (nor therefore the anchor) because the disengaged safety line will slide out of the eye on the rope that was holding you to the scotchman. Your boat is free to float away, but you can still go back to retrieve all your gear attached to the scotchman.
So as you can see, the safetly line comes in quite handy. Without it you just have all sorts of problems. If you attached the rope from the scotchman to your bow, it's hard to release in an emergency. And if you attach the rope anywhere else, your bow won't face the current the way you want it to (for reasons already mentioned).
Hope this helps.
It is also quite useful when you retrieve your gear.
Remember, it's called "fishing," not "catching."