Posted 2019-January-10, 06:10
Thoughts:
1. Just because the sequence you chose missed a slam doesn't necessarily mean you did anything particularly wrong. The problem is that robots are particularly terrible at latter round 2/1 bidding and slam bidding, they don't know how to cue bid properly or evaluate hands sometimes. So you may bid perfectly reasonably and miss slam because robot partner fails to cooperate, or take over captaincy as appropriate. So sometimes when you miss slam with GIB you just have to shrug your shoulders and rage at the programmers for the slow pace of improvements. If you try to overcompensate by overbidding/misbidding your own hand, you'll tend to get to a lot of hopeless slams (some of which might luckily make due to GIB's inept defense), and this will be detrimental to your play in human games in the long run. Good slam bidding requires partnership cooperation and good system agreements, so it's often pretty random and bad when playing with either robots or beginner/int level humans.
2. Immediate blackwood is clearly wrong for a number of reasons. Normally, to bid blackwood, you want minimally both (a) all unbid side suits controlled (because bidding slam then watching your opponents simply cash king and ace of a suit is bad), and (b) know that you have enough overall strength to take 12 tricks (because even if the opponents don't have two aces off the top, or ak off the top in a suit, it does you no good to bid the slam if you don't quite have enough tricks in the end). Here, you have two suits with 2 fast losers initially, and a slightly above minimum GF that requires partner to have substantial extras to get into the slam zone (generally around 32/33 combined points including distributional values, less if one can determine hands mesh together particularly well). So it's best to describe your hand first and find out about partner's.
3. Your choice of 2d then 4s is actually quite good IMO -- if playing with a human good bidder. Normally this describes a min range GF hand with good diamonds and good spades with no control (ace, king, singleton/void) in either clubs or hearts, or basically exactly what you had. A so-called "picture bid", it is more descriptive than 3S, which just shows fit and doesn't describe the concentration in the two suits and lack of control in the others. Partner normally expects more like 4252, one more diamond, one fewer spade, but so what, to me this is by far the closest, most effective description. One bids the non-jump 3s rather than 4S holding hands with hands with spade fit not suitable for picture bid, hands with more scattered values, control in a side suit, and partner will expect often 3 cd support only.
Now opposite any decent human partner, a picture bid should get the job done; partner is looking at substantial extras, controls in both H and clubs, and the DQ which will look like a very useful card. It's clearcut blackwood by NORTH at this point, bid slam if not off 2 keycards. So blame your partner on this one.
4. Jacoby 2nt is another alternative; I like it less on this hand since the "picture bid" sequence of 2/1 is so descriptive. But it is the normal usual choice holding 4+ spade suit and no side shortage if the values were more scattered.
5. If you want to keep forcing in 2/1, after having made the 2/1, anything that isn't game is forcing.