Suzanne D. wrote:

I inherited a bunch of grape vines last year. I know nothing about
grapes, but have tried to learn about pruning from the internet.

Our plants have thick wood at the base; I don't know how old they are, but
the trunks are about two inches across; maybe about five inches in
diameter.

I tried pruning them yesterday, and discovered that the trucks go a
LOOONNNNG way before sending out canes.

Probably due to improper pruning when they were young. Grape vines have
what is known as terminal dominance. The energy will go to the end of the
cordons first. If the cordons were too long initially, all the energy went
to the ends.

You could consider "Heading" the vines. This means severe pruning in which
you cut back to where the trunk, or more properly called Cordons, go from
vertical to horizontal on the wire. New shoots will grow from near the
head and you can train them to be your new cordons (horizontal portions of
the trunk). You will have very little or no fruit the first year after
this procedure. After the new cordons go dormant in the fall, prune them
back to about a foot or 18 inches in length and every year you can extend
them about 6 inches or so until you have the cordon length you want. After
dormancy, prune the canes growing from the new cordons to create two bud
spurs on the cordons. This is for cordon / spur pruning. If you decide to
go with cane pruning (which is slightly more difficult to learn how to do
properly) you can leave two canes about several feet in length. It is
important to know what variety of grape you have because some varieties
produce very well on cordon / spur pruning but a few varieties do not have
very fruitful buds for the first several buds and therefore you need to
cane prune the vine.

I highly recommend the book "From Vines to Wine" by Jeff Cox - even if you
are not growing the grapes for wine production. It is one of the best book
I have found on pruning and is very inexpensive. It has numerous line
drawings showing you how to prune from year to year.