To add to Martin's comments (concur 100% BTW). I have two boats that I use on my lift, and they couldn't be any more different. I've adjusted my bunks to be a good compromise between both setups. The Bass Cat gets pulled in the stall, a single rope tied to the front cross bar of the dock is hooked on the bow eye, start the lift, and push the boat back somewhat in the center. The angle of the hull does the rest of the work to center the boat on the lift.
For my inboard ski boat (flat bottom in the back half of the boat, I use two ropes tied off at apprx 45 degree angles to the back of the boat. Pull into the stall, hook the ropes on the cleats, begin raising the lift, slide the boat back against the ropes (centering it). Been doing this since my dad first got his first Boat Floater in 1977.
Not to be a commercial, but he's had three diff't Boat Floaters over the years as his boats got bigger. I bought mine 13 yrs ago. All of them have been fantisic...great product for sure.