G'day Claude,

What is your priority here, covering the pergola you wish to
build or growing a grape vine? I'm not having a shot here, it's just I'm
more interested in the choice of grape, rather than how it's held upright.
If you are going to use this vine to produce fruit or leaf, you are going to
be cutting back the bulk of each years growth every winter, thus reducing
the stress on any supports. With the years, the 'trunk' of the vine will
become self supporting, grapes live for eons and I'm told that some wine
makers prefer old vines for quality if not quantity.
If you want privacy from this vine then please consider that
it will be bare for five or so months of the year, and the rest of the
year, the birds will be 'you know whating' all over your deck while they
argue about which flock will eat your grapes and leave droppings all over
your car.

Build the pergola you want, then choose your plants, if you
really want grapes, then I advise you not to plant it near your back door.
There are a number of ornamental grapes, chosen for their leaf colour and
they don't fruit, but they are still deciduous.

China
Wingham
NSW