mw64ahw, on 2021-July-21, 13:56, said:
I'm saying that a strong hand versus a minimum opener has de facto slam potential. Likewise for an Intermediate hand opposite an Intermediate hand. 4/5♠ should be safe in either case so you can use Italian cue-bids to establish initial slam viability from 3NT to 4♥ and can sign-off in 4♠ or continue key-card showing/cue-bidding/sign-off in 5♠ or bid the slam if desired. I don't think you need the additional space by using 2♥ so this can be used as the Limit/Min bid to establish whether game is feasible and the strain. As it stands you may miss game using 3♠ as NF. Regarding 4♠ I was just interested if you envisaged any hand shape/strength that would sign-off directly.
My own structure is Transfer-Walsh based with 1♠ as GF which remains after 1♥ interference. Completing the transfer after the X shows 3♠ and a limited hand, but I like the idea of using 2♥ for a limit response.
Over the double my 1
♠ is not a minimum, unlike mikeh's. This means that opener still has a wide range. I think this pays off when responder is weak with 5 or more spades - if opener does not mention the 3-card support in a strong hand immediately it can be hard to tell if we have established a fit if the opponents intervene. One good (better?) alternative is to have several different strong responses - 2
♦, 2
♥, 2NT maybe - clarifying not just strength but also spade length, so that 1
♠ can be NF.
Jumping with SI looks quite bad to me. Having extra space to describe the level of slam interest is very helpful, to the point of being vital, if 1
♠ is unlimited. Not to mention that I absolutely loathe jumping on slam auctions unless the jump is very narrowly defined. The 3
♠ bid you mention is very rare, most hands with game interest will bid 3
♣, 3
♦ or 3
♥, so that 3
♠ is tightly defined by negative inference. Keep in mind that all these bids are very limited - about 10-11 points of playing strength.
Responder can't jump to 4
♠, opener is practically unlimited. Any (minimum, shapely) hand that decides that 4
♠ is the right spot would have jumped on the previous round. 1
♣-(1
♥)-2
♠ is 8-11 with 6(+) NF and higher bids in spades are weaker and longer.