post spacing for trellis

[franc1969]

What spacing would I use for trellis posts? Metal posts, like sold at Orchard Valley Supply. This is probably where I'll get the line posts and crossarms, though I have found similar posts locally for end posts. I am not finding info here or googling, just vine spacing. I am sure I am just missing it at this time of night.
I have pulled the plug on muscadine vines for eating, and Cynthiana/Norton for wine. I think I may use the same for my moved blackberry trellis too. Different spacing and weights to support, I know, but where to start? I have some time, but I want to get things in place before I plant.

 

[NoQuarter]

For muscadines you need to plant 20 ft. apart. Use very heavy post and #9 galvanized wire with some form of tensioner as they can put on a lot of growth each year and up to 80lbs of grapes each. I use railroad ties on both ends and 4x4 post every 20 ft between wines. perhaps overkill but They have lasted over 20 years now. 1 wire at 5ft. high.
For the norton I think its 6x9 spacing but I am not certain. Someone who grows them might chime in.

 

[Rice_Guy]

each of my northern hybrids have an eight foot metal post which carries most of the weight