Gould

Could I get an estimate of chain needed for my 31 foot ChrisCraft, all wood,
approximately 10,000 lbs.

If it were mine, I'd use at least 30 feet
of 1/2" chain, but you might "squeak by" with 3/8.

3/8 weighs about 14 pounds per ten feet.
1/2 weighs about 26.

That said, there are other factors to consider.

Where do you plan to anchor? If a lot of the prospective anchorages are fairly
deep, or crowded, you will want to use significantly more chain so that you're
not swinging a mile with every little shift in the wind or current. One of the
big advantages of more chain is that it your hook will continue to hold at low
scope levels that would fail in an all rope approach.

Out where I boat, we get 13-14 foot tide changes fairly routinely. Takes a bit
of noodlin' and a little more scope to be prepared for the impending additional
depth when anchoring at low tide.

"Chain" is not always chain. You're likely to have a windlass on a 30-footer,
so make sure you get a chain with properly configured links. Some chains, (BBB
for example), seem to mate up with the gypsy
more accurately.