Hola Pablo
Somebody on another forum:http://www.sailboatowners.com/forums/pviewall.tpl?fno=122&uid=73209970012&sku=2004159061734.7&rid=2004161063901.95had this advice:"Place the canvas over the snaps. Using a crayon or pencil, lightly rub the area over the snap. It will reveal the spot where you place the snap on the new canvas."To hammer the snaps onto the canvas you need a solid surface, most likely _off_ the boat, but perhaps a portable anvil or something would do.I'd be afraid to mark all the snaps and then hammer them all in at once. I think you might not get it smooth no matter how many hands you had to hold the canvas in place. Perhaps I'd try marking two at the top end (forward end of hatch), then hammering on the smaps, then snapping it into place and smoothing it out, and _then_ mark and install two snaps at the other end of the canvas (bottom of companionway door). Now the canvas would be locked in place and not move around as all the rest of the snaps were marked. Then install all the rest of the snaps or, if you're still worried, a few at a time. The idea is to anchor the end points first to avoid buckling and humps between the snaps along each side and the forward edge.That's what occurs to me, but since I had no snaps on the boat I haven't exactly done what you need to do. I installed all snaps on the canvas, but then marked and installed just the end ones on the deck similarly as described above so I could snap it in place, and then I finished all the rest of the middle ones....RickM...