to tension the shrouds solo raise the sail, travel out to the side you want to tension and sheet in. Don't tighten it too much or the mast won't rotate right. This works better than a person hanging from the trap wire so make sure you aren't overtightening. On a 14 or 16 you would have to raise the sail. On an 18 or other similar boats you can just attach the halyard to the end of the boom.

-Todd