Claude wrote:
I want to build a pergola to support a grape vine over the deck. I need to
span 6 metres and am thinking the only practical way to do this is to use
some form of parallel wires (eg tensioned stainless steel like they use on
yachts) set out at say 500mm centres. I'm wondering if anyone would have an
idea if this would work or whether the weight of a fully grown vine would
eventually lead to sagging wires?


Depending on thickness of cable, and the tensioning technique it should
hold the weight OK.
Look at other pergolas in your area. You may find, if youre building the
frame out of wood, that you would have to make sure the tension is
retained at both ends...without anything collapsing. So reinforcement to
carry the weight would also be an issue.
A metal frame sounds like it would work...
Sagging wires would be the least of my problem. They would get covered
by the vine anyway...