Thank you all for your replies.
This is the splinter bidder's hand.
As you can see, any bid other than 4
♠ will get you to an almost cold 6 spade contract. Only possibilities of going down would be a diamond ruff on the opening lead or a club lead follow by a heart ruff, if spades are 4-0 there are some handling problems but not insurmountable. (sp?)
Another small confession is that I was the one who doubled and then splintered on this hand. I actually can't remember the last time that I made this type of bid. The comments that I made in the introduction have been told to me by others.
I could have also X ed, then cue-bid hearts, and then splintered I guess, but I chose not to because as I said this was with an unknown partner who may not be on the same wavelength as me. I tried to show an immediate raise, with a splinter for partner, with game points who was willing to play in 4 spades opposite xxx
♠ and 0 points (although I obviously would hope for something, even a little shape).
I tried to show the bidding from my partners point of view and it seems to me that partnership trust and knowing partner's bidding style played a big part in South's decision to sign off in 4 spades.
Cheers,
Theo