I'd want a minimum of 16ft for two vines but have done with less. Don't recall your other post. But I started out using the four arm Kiffen or whatever it's called. Then I decided that most of the vigor went to the two upper arms so now just go with two arms up pretty high, about 6ft. If you want more grapes on a shorter trellis I'd go with three wires. Have the canes on the middle wire and another wire on each side at the same height to spread out the canopy. Potential yield is directly correlated to the amount of sunlight intercepted. So making the canopy longer or wider will increase yield, or eating quality if you limit yield by cluster thinning.

Thanks fruitnut. So actually a 16 ft. trellis would be great for one variety alone?

The general wisdom for bunch grapes is 10 space per plant but as Fruitnut said more just helps. The 10 foot spacing yields the most per acre and that is all the coms really care about.

For muscadines 20 foot per vine.

The triple wide top wire that Fruitnut mentioned is called a Geneva double curtain if you want to look it up.

Just chiming in with what I did with mine. I have a Venus seedless that I bought two sections of split rail fencing for.

:==:==:

Planted the vine along the middle pole and am training the limbs across the top and bottom horizontals. I'd say off the top of my head they're probably 8' beams, so 16' total.

This is the vine's second year and its already covered about half of it.