Transfer and Shape Bids
Transfer and Shape bidding after opponents open a strong NT or strong 1♣ (precision) hand.
In competitive auctions, we value keeping the overcaller as captain of the auction. The transfer request allows that option.
Overcaller bids 1 below the intended suit to show a competitive 6-card suit; a transfer request. The examples below apply after opponents open a strong 1NT. Strong NT has 15 HCP in its range. See TRaP bidding when opponents are playing 12-14HCP (or weak) 1NT
Dbl -> Both Majors or Both Minors 2♣ -> Diamonds 2♦ -> Hearts 2♥ -> Spades 2NT -> Clubs 2♠ -> Spades AND a Minor 3♣ -> Clubs AND Hearts 3♦ -> Diamonds AND Hearts
Other very competitive hands are two-suited. Applying Mel's rules of competing in NT, we wish to show almost all two-suited hands (5-5 or better). The 2♠ bid shows Spades and a minor.
We find that a penalty double of 1NT provides little value. The only case the yield good tournament results occurs when opponents are vulnerable, and if you know that they are prone to some questionable 15 HCP opening choices.
The Double of 1NT shows either a two-suited hand in the minors or the majors. Partner should bid the minor they'd prefer to play, and an overcall corrects by bidding hearts to show they started with 5-5 in the majors instead of minors.
The final two-suited hand types to show are hands with 5 hearts and a 5-card minor. The bids of 3♣ and 3♦ show 5 of that minor plus a 5-card♥ suit. Since this overcall forces the auction to the 3 level, the overcaller should have some extras in their valuation.