After 1♠ (5+♠, 11-15 hcp):
1NT - forcing inquiry. Most weak invitational hands go via here. Opener will not respond above 2♠ without a freak (7♠, 6♠-5m, 5♠-6m). Responses show min/max/4♥/6♠
2♣ - either a hand that wants to play in 2♦, or 5+♣, 12+hcp
2♦ - either a hand that wants to play in 2♥, or 5+♦, 12+hcp
2♥ - either a hand that wants to play in 2♠, or 5+♥, 12+hcp
Opener will always complete the transfer unless he has a freak (as defined above), or excellent ♠ and 0-1 in the weak suit.
If responder has the weak suit he won't bid again, and opener is encouraged not to compete to the 3-level without something special.
With 12-13 responder will bid 2NT, which opener can pass with 10-11. This also suggests holding 0-1♠: 1♠ 1NT; 2x 2NT suggests 12-13 with 2♠
With anything else responder bids a suit - this is GF, e.g. 1♠ 2♦*; 2♥* 3♣ = GF with 5♦ + 4♣, 1♠ 2♦*; 2♥* 3♦ = GF with 6♦. Thereafter natural bidding ensues.
Raises
We have plenty. All immediate responses from 2♠ onwards show support, and also some sequences that start lower.
1♠ 1NT; 2x 2♠ - this would include a very balanced 8 count with 3♠ amongst other possibilities
1♠ 1NT; 2x 3♠ - a very balanced 14-15 count with 3+♠
1♠ 1NT; 2x 4♠ - sound hand 5♠, weak slam interest
1♠ 1NT; 2x 2NT - 12-13 count with 2♠, not really a raise
1♠ 1NT; 2x 3NT - to play as direct 3NT was artificial, not a raise
1♠ 2♣*; 2♦* 2♠ - GF, 4♣, 3+♠
1♠ 2♣*; 2♦* 3♠ - GF, 5♣, 3+♠
1♠ 2♣*; 2♦* 4♠ - GF, 5♣ poor club suit just 1 of top 3, 3+♠
...same pattern as above but with a ♦ or ♥ suit
1♠ 2♥*; 2♠* Pass - 2-level preempt. We are using this more recently with just a small doubleton in support, no regrets so far.
1♠ 2♠ - 9-11, 3+♠, no shortage. We use 3-way trials after this.
1♠ 2NT - mini-splinter 7-9 in unspecified suit 3+♠, or unspecified void splinter; relay asks
1♠ 3♣ - 12-13 with 3+♠ - we can play in 3♠ if opener has 10-11, or GF with support no more descriptive bid. Like 'Jacoby' with invite+: 3♦=min, 3♥= unspecified shortage, ...
1♠ 3♦ - prime 10-11 with 4♠
1♠ 3♥ - GF good unspecified suit with 2 or 3 of top 3, 3+♠; relay asks
1♠ 3♠ - preempt to 3-level
1♠ 3NT - midi-splinter 10-13 in unspecified suit; relay asks.
1♠ 4x - maxi-splinter 14-15
1♠ 4♠ - pre-empt to 4-level, or good hand with no slam interest
We also use a similar pattern after 1♦ (0+♦) also, but 4 transfers starting from 1NT.
It's hard to be objective about this. Every system has occasional hands that are hard to bid, and after a while you stop noticing and bad results, how frequent is this and is it outweighed by gains elsewhere?
+ If you have one of the weak hands, this should be good. Opponents need to start exploring at the 3-level.
+ If you have support it should work out well - we have the raises covered: although some of the sequences quickly get you quite high, there are ways to establish forces at a low level too.
+ Increases variance. For us, this is a positive.
? Maybe most of the benefit comes just from making a limited opening ... not getting too high, or jumping to game without revealing your hand.
? It seems a little backward in a constructive auction, that opener has already made a good start describing his hand then responder takes over the next two rounds describing his hand. I concede that a full relay system starting with say 2♣ is likely to be better, but that violates the 'keep it (reasonably) simple' rule that we need.
? Some shapes work better than others - 1♥ 1NT*; 2♣* 2♠ - GF with 6+♠ seems like a great start; but 1♠ 2♦*; 2♥* 3♥ - GF with 5♦ + 4♥ is not so good.
- Overall slam bidding must suffer a little, compared to 2/1 at least.
- If for you 1♥ 2♠ or 1M 3m is a pre-empt then you lose that.
One of the difficulties with a 'roll-your-own' system is that you don't have a body of people contributing improvements: where would standard bidding be without check-back, fourth suit forcing, reverses, splinters, conventional 2NT, etc? If anybody is interested in trying this, there is not much more to it. I can set out the relay responses we use, and a few notes about competition.