i want to put a pocket on my vinyl tramp for storing the halyards.What size are they and what material is best

A good alternative are zippered pouches available from Murrays (page 61, 5"x12" works well). Clip the pouch to the tramp center lacing.

Zipper bags are terrible on beach cats. I don't know why they still make them.

I have a standard sewing machine. Nothing fancy. I bought an old mylar wind surfing sail on Ebay for $20. I got it and sliced it up, sewed a tramp bag with velcro. I had enough material to make 12 good sized bags.

10 of them are to be Xmas presents to friends in the fleet... ha ha ha. Cheap and better than Murrays.