[helene_t]

Yesterday uqx (David) and I had a misunderstanding during a club game:

1♦-(pass)-1♠-(2♥)
dbl-(pass)-2♠-(pass)
2NT- all pass

I thought my dbl followed by 2NT would show 3-card support and some 17-18 points. With 15-16 I would have passed 2♠ with 3-card support, and passed 2♥ with a doubleton spades.

David thinks I showed 15-16.

I know support doubles are not usually played in a weak notrump context. But if I have to double with all 15-16 balanced hands, I would think it would be difficult for p to decide what to do with, say, a 4333 or 4234 and 6-8 points.

We play lowest-fourcard Acol and (I think) Walsh.

[Stephen Tu]

Some years ago I asked Eric Kokish about this situation, following is his recommendations at the time:
##
My agreements are the same in all three cases. Double shows either a
sound three-card raise (side SPL or a strong NT) or a strong balanced hand
that can't afford to pass (theoretically 18-20). Responder uses
lebensohl-style replies.

With a normal strong NT and only two-card support, we generally pass,
placing the partnership onus on responder, who is expected to reopen with
DBL if game is possible opposite such a hand, or with a suit bid, generally
showing a bit less. Rebidding his major shows 6+ cards and covers a slightly
wider range.

A raise to 2M implies 4-card SUPP and either a shape hand (4S5m22 is
possible but after a 1H response, a SPL is expected as we open 1NT with 2452
and 2425 and 11+-14) or a strong NT (we treat those hands as virtual
equivalents). Responder tries for game if he would do so opposite a strong
NT, using the partnership high-powered game try/slam try machinery (it's
very good stuff and necessary when a raise can cover so much ground).

For the record, Martel/Stansby's philosophy is very different from ours,
both as to the simple raise(might be 3, with a strong NT and 4, jump to 3M)
and to the DBL (any strong notrump unsuitable for a raise).
##

[2nt by opener is played as good-bad].

[Cascade]

I would double with most balanced hands in the 15+ range with three spades. I might not with some hands that are well fixed in the opponents suit preferring either to PASS (nearer 15) or bid 2NT (nearer 19 - actually we can't have 18-19 as we play a 2♣ opening for that hand).

Most hands with only two spades I will either PASS when near the lower end of the range or bid 2NT with the upper range.

Our doubles don't show three-card support so I might occasionally double with a strong doubleton - I had one a day or three back where I doubled with ♠ AK (although I can't remember the precise auction).

We also double with other non-balanced hand types.

Some good advice I got once - never be afraid to defend with a strong balanced hand. I suspect that my first tendancy to want to bid some more in these auctions is still too strong and that I would do better by passing more often. They seem often to be misfit auctions and when they are not partner can sometimes take some action.

Obviously from the above I play 2NT as natural on this auction.

[fromageGB]

Funny that nobody has addressed the question.

I think support doubles are valid with any NT strength, and use them whether playing weak or mini.

Firstly, playing 12-14NT, a rebid of 2NT (not in the context of this hand) shows 17/18, so it is not a bad idea to assume the same here, without discussion.
Secondly, partner could have taken some other action than 2♠ with a 11-12 count, so he is probably in the range 6-10. That being the case, a forward move over the 2♠ invites him to go for game if he is upper range, so I think 17/18 is better than 15/16. I, myself, would assume a 17+.

Another factor is how strong you agree a support double to be. If you agree 15+ then it has to be 17+ to bid further. I would support double on a good 13, and then 15+ becomes arguable, but with that I would not want to invite partner to go on with a 9 count.