I don't think they actually meant the block is attached to the beam. Robi set mine up for me. It is just a turning block attached to the tramp, with a bungee, near the the rear cross bar. The purpose is to keep the spin sheet from sliding out of reach.
I too am having problems sliding across the boat and plan to add some non-skid to the deck.
My only purpose in placing the spin block near the rear cross beam is to have an anchor point that is near the rear of the boat, rather than the front of the boat. When the boat slows quickly, this provides stability for me on the wire that a forward point does not. A bungee cord does not seem like good idea for attaching the block for this purpose.
My rear block is a snatch block (one that I can open as needed to add or remove the spin sheet). I used this type block so I could switch the position if I had a crew member, or in case I needed more spin sheet slack.
Having said that,I admit I am no expert in this solo spin while trapping subject. I am here to learn.
