What zone are you?

I'm no expert but table grapes are usually grown on a top wire with downward hanging canopy. Depending on your vines vigor at 13' I would say you have place for 1-2 vines. I grow on a Geneva double curtain and my grapes are at 8' apart and can easily fill in 16' of canopy (8'x2 parallel wires) and reach for more. Multiple wires over each other will shade the lower bunches which will retard/inhibit ripening.

For more info:

http://smallfarms.oregonstate.edu/sites/default/files/publications/growing_table_grapes_ec1639_may_2011.pdf#page6

http://msue.anr.msu.edu/uploads/files/e2774.pdf

http://www.extension.umn.edu/garden/yard-garden/fruit/growing-grapes-for-home-use/

Two wires is plenty and two plant would fill that thing. If you want to prune aggressively 3 may fit I'd start with 3 knowing you may have to get rid of one , or find more trellis like

geneva I actually use three high wires four feet apart plant every five feet then alternating on top wire. Grapes can be shaped however you want but fruit needs space and

air.