I tried shortening my spin sheets and the block on a bungie at the back of the tramp, but then when I trapped out downwind, or when on a high, tight reach, the sheet was too short! So I added a pigtail from the clew, spiced into the sheet, and got rid of the block at the back.

Yeah, there is sheet all over the tramp when going upwind, but at least I get quick, clean jybes and have a long enough sheet for trapping out at the back of the boat.

almost as if you need two spin sheets: one for buoys and one for distance. Set up slightly different based on the demands of the two disciplines.

Yeah, if you are going to spend all day out on the wire at the back of the boat with a spin sheet, you'll want a much longer one than for bouy racing.

If you plan on changing the sheet, do consider a 2.5mm or 3mm D12 line the length of the normal sheet + 1 metre. Simply divide the length in 2 and then adjust so that one length is 1m longer than the other. Now at the midway point use a hitch through the clew, lock it off by going through twice before taking the tails through the hitch. You now have a nice line which doesn't catch on the forestay ( no knots ) and seperate tails which you can take back through the blocks for when you take off the spinny from the boat.

Buy some " soft cover " and place over the thin D12 either just where you handle the sheet or if you are worried about grip on the blocks, up to the block, back to the end of the D12, sew in place to lock the cover off at the start and finish. Once through the blocks, half hitch the tails together. You are now left with a single line from approx. the more normal sheeting position to back to where you will wire from.

Why use D12 at the front, it doesn't seem to burn the chute when you are snuffing, much cheaper to buy D12 and cover than sheet which can be ever so expensive, lighter and best of all has almost no weight at the clew end of the spinny. Ask your rope supplier and he will almost certainly have a great big length of cover sitting about where it has been stripped from another line.